Biomechanics doi: 10.3390/biomechanics6020048

Authors: Zihao Liu Simin Li Vadim V. Silberschmidt

Background: Trabecular-bone adaptation (TBA) continuously reshapes the trabecular-bone (TB) microstructure at the microscale in response to mechanical loading. While organ-scale adaptation has been extensively studied, the mechanisms governing the evolution of individual trabeculae remain inadequately understood. Methods: This study proposes a new remodelling model: under finite remodelling capacity, surface regions that satisfy mechanostat criteria compete for remodelling events according to the spatial non-uniformity of local mechanical stimulus. This model uses a two-criteria remodelling scheme that combines (i) a mechanostat criterion for bone formation and resorption and (ii) a distance-weighted non-uniformity criterion. The model is implemented with a 2D finite-element framework using a USDFLD subroutine in the Abaqus/Standard software package. Idealised X- and I-shaped trabecular geometries are subjected to controlled bending, compression, and shear load cases to examine loading-dependent morphology evolution. Results: Compared with the corresponding one-criterion models, the two-criteria framework produces a lower fraction of active remodelling surface and a more clearly bounded convergence process. The numerical simulations reproduce characteristic plate-like morphologies of trabeculae under bending and rod-like morphologies under compression, while additional variations in thresholds and loading conditions shift the response towards resorption-biased structures. Conclusions: The results indicate that the mechanostat criterion primarily stabilises the global bone mass, whereas the non-uniformity criterion governs where remodelling is preferentially located on the trabecular surface. The proposed framework therefore provides a microscale and mechanistically interpretable basis for analysing loading-dependent morphological adaptation of individual trabeculae.

Biomechanics doi: 10.3390/biomechanics6020047

Authors: Guillaume Claus Joe Abi Nader Laurent Fabeck Alphonse Lubansu Patrick Salvia Benoit Beyer Véronique Feipel

Background/Objectives: The A-Palp enables a calibrated anatomical systems technique (CAST) approach. Previous studies have demonstrated repeatability and concurrent validity for selected spinal curvature angles in patients with scoliosis. However, the inter-operator reproducibility, temporal repeatability, and reliability of sagittal spinal curvature measurements and spinopelvic parameters remain to be established. Methods: Eighteen healthy adults without spinal pathology were assessed. Two operators sampled sagittal spinal profiles with the A-Palp in a 14-camera optoelectronic setup, applying reflective markers and palpating spinous processes. One operator repeated measurements after seven days. Marker data were processed in MATLAB (R2019b) to smooth trajectories, fit curvature arcs, and compute extracorporeal kyphosis, lordosis, and pelvic parameters. Reliability and repeatability were evaluated using Bland & Altman analysis, intraclass correlations (ICCs), standard error of measurement (SEM), mean detectable change (MDC95), root-mean-squared errors (RMSEs), and Statistical Parametric Mapping (SPM). Results: Reliability and repeatability were strong. For global spinal angles, ICCs exceeded 0.90 across operators and sessions. The tangent method yielded low SEM (1–2°) and MDC95 (3–6°) values, whereas the circle-fit/trigonometric methods showed larger errors. Most spinopelvic angles had moderate-to-excellent ICCs (0.65–0.98) with SEM/MDC95 values ≈2.1–4.5°/5.9–12.4°. Ground reaction force-referenced distances showed good ICCs and small intra-operator error (SEM: 3.8–4.8 mm; MDC95: 10.7–13.4 mm) but wider inter-session thresholds (SEM: 10.3–11.6 mm; MDC95: 28.6–32.8 mm). Bland & Altman biases were ~0, with narrower limits for the tangent (≈±5°) than circle-fit/trigonometric (≈±8–12°) methods. Curve tracking was consistent (RMSE: 2.7–3.7 mm, <5% amplitude), and SPM detected no point-wise differences. Conclusion: The A-Palp method demonstrated high reliability and repeatability for extracorporeal sagittal spinal and sacro-spinal evaluation. Variability was low across operators and sessions, supporting its use as a robust, non-invasive clinical and research tool.

Biomechanics doi: 10.3390/biomechanics6020046

Authors: Tingyu Dai Robin Reinardt Michael Roland Stefan Diebels Bergita Ganse Marcel Orth Gargi Shankar Nayak

Background/Objectives: Strain energy density-based algorithms are widely applied in modelling bone healing, yet their use under patient-specific geometry-based conditions remains underdeveloped. This study proposes a patient-specific geometry-based framework for fracture healing simulation and investigates how different postoperative loading conditions influence the mechanical environment of callus remodeling. Methods: Using postoperative radiographic data of a 63-year-old male patient with a distal diaphyseal tibial fracture and concomitant proximal and distal fibular fractures, a three-dimensional finite element model of the tibia was reconstructed, imported into a multiphysics simulation environment, and coupled with an iterative numerical algorithm. A uniform initial callus density of 750 kg/m3 was assumed as a simplified and homogenized representation of the healing tissue. The effects of different mechanical loading conditions (partial weight-bearing, physiological loading, and supraphysiological loading) on the mechanical response and density evolution of the callus were evaluated. Results: Partial weight-bearing resulted in insufficient mechanical stimulation and progressive density loss within the callus. Physiological loading generated strain energy density levels consistent with known osteogenic ranges and contributed to continuous cortical shell formation and overall density increase. Supraphysiological loading was associated with overload-related resorption and spatial heterogeneity, which may reduce callus stability. Conclusions: The findings suggest that loading magnitude may influence the simulated remodeling response of the callus under the assumptions of the present model. These results indicate that intermediate loading conditions were associated with a more pronounced remodeling response compared to reduced or excessive loading for the investigated case. The comparison with postoperative clinical imaging showed qualitative agreement in the spatial distribution of mineralized and less mineralized regions, supporting the feasibility of the proposed patient-specific geometry-based SED-based framework.

Biomechanics doi: 10.3390/biomechanics6020045

Authors: Alessandro Scano Nicol Moscatelli Valentina Lanzani Cristina Brambilla Lorenzo Molinari Tosatti

Background/Objectives: Industry 5.0 emphasizes the protection and empowerment of human workers. Passive wearables reduce physical strain, but the evaluation of their efficacy remains incomplete when based solely on kinematics or electromyographic (EMG) envelope amplitude, failing to capture the underlying neural “cost” or the compensatory strategies. This paper proposes a computational framework centered on muscle synergy analysis to bridge the gap between laboratory-grade neural assessment and real-world industrial applications. The goal is to move beyond simple biomechanical metrics toward a deeper understanding of neural coordination during device interaction. Methods: Given the practical limitations of high-density EMG in industrial settings, we propose a “streamlining” approach: laboratory-derived synergy models guide the understanding of neural processes and the selection of a minimal set of sensors capable of detecting maladaptive motor compensations and early signs of fatigue. Results: This approach allows for long-term monitoring without compromising natural movement. By decoupling neural strategies from kinematic output, “silent” risk situations can be identified even when movement appears correct but the neural coordination is altered by the passive device. This supports personalized ergonomic indices and predictive prevention protocols, transforming wearables from simple mechanical aids into intelligent, human-centric systems. Conclusions: This framework provides a roadmap for translating complex motor control theories into practical tools for the next generation of safe and sustainable manufacturing.

Biomechanics doi: 10.3390/biomechanics6020044

Authors: Weerasak Tapanya Noppharath Sangkarit

Background: Standard clinical scales for pediatric and adolescent ataxia lack biomechanical granularity, limiting precision rehabilitation. This study aimed to identify compensatory gait phenotypes using unsupervised machine learning and establish a robust, highly accessible clinical decision model. Methods: Spatiotemporal gait data from 51 youths (31 ataxia and 20 healthy controls) were analyzed. To ensure pathological specificity, Principal Component Analysis (PCA) and hierarchical clustering were applied exclusively to 13 biomechanical variables from the ataxia cohort (n = 31) to extract underlying domains and identify patient subgroups. Healthy controls were subsequently used as a normative reference. A Classification and Regression Tree (CRT) algorithm was developed for clinical translation. Results: Two distinct phenotypes reflecting the evolution of compensatory strategies were identified: a “Rapid Rhythm” strategy (n = 24) and a severe “Prolonged Stance” strategy (n = 7). Unlike previous assumptions, the phenotypes strongly correlated with clinical severity (Scale for the Assessment and Rating of Ataxia (SARA) scores: 9.79 vs. 16.78, p = 0.012) and exhibited significantly different gait speeds (p < 0.001). The CRT model identified the stance phase duration as the primary discriminator. A recalibrated critical cut-off of >69.68% effectively classified the severe Prolonged Stance phenotype. This threshold sits distinctly above the healthy pediatric norm, achieving an overall cross-validated accuracy of 96.8%, with 100% specificity. Conclusions: Gait phenotypes in pediatric and adolescent ataxia represent progressive stages of neuromechanical compensation driven by disease severity. The established 69.68% stance-phase threshold provides clinicians with a powerful, single-variable biomechanical red flag to identify severe pathological gait and guide phase-specific precision rehabilitation.

Biomechanics doi: 10.3390/biomechanics6020043

Authors: Kendra S. Graham Joshua T. Weinhandl

Background/Objectives: While restricted dorsiflexion range of motion (DF-ROM) is linked to deleterious sagittal and frontal plane knee and hip kinematics during landing, the literature is conflicted as to whether excessive foot pronation is linked to knee injury. The purpose of this study was to examine the relationship between static foot posture, DF-ROM, and lower extremity biomechanics during a drop-landing task. Methods: Fifteen physically active adults (age: 22.6 ± 2.4 years, height: 1.69 ± 0.08 m, mass: 66.40 ± 9.95 kg) volunteered to participate in this study. Static foot posture was measured by the six criteria of the Foot Posture Index (FPI-6) and DF-ROM was measured using the weight-bearing lunge test (WB-LT). Sagittal and frontal plane kinematics and kinetics of the hip, knee, and ankle were captured using a 3D motion capture system and force plate during a drop-landing task. Results: FPI-6 scores (4.67 ± 2.94) correlated with knee abduction angle at initial contact (1.08 ± 3.30°, r = −0.59, p = 0.02), ankle sagittal plane excursion (39.11 ± 7.67°, r = −0.63, p = 0.01) and knee adduction moment (0.58 ± 0.51 N/kg, r = 0.60, p = 0.017). DF-ROM correlated with knee adduction moment (r = −0.59, p = 0.02). The combination of FPI-6 and DF-ROM accounted for 56% of the variance in knee adduction moment (r = 0.746, p = 0.008). No significant relationships were identified for hip variables (p > 0.05). Conclusions: Participants with a more pronated static foot posture displayed less knee adduction angle at initial contact and decreased ankle sagittal plane excursion. Those with less DF-ROM and a pronated static foot posture exhibited increased maximum knee adduction moment. Foot and ankle structure influence lower extremity biomechanics.

Biomechanics doi: 10.3390/biomechanics6020042

Authors: Daniel Dantchev Svetoslav Nikolov Gergana S. Nikolova

Background. Walking is a fundamental human activity, vital for daily living, social connection, employment, etc. Methods. In the current study, we present a mathematical model of it, based on the planar double pendulum system influenced by gravity. For parameters of the pendulum, i.e., the characteristic of the limbs (thigh + shank), we use realistic mass–inertial parameters. The model incorporates anthropometric and inertial data specific to the average Bulgarian, Russian, German, and American male, including segment masses, centres of mass, as well as densities of the segments taken from experimental studies. Results. We derive the corresponding nonlinear differential equations governing the model. We solve them analytically, when possible, and, in the general case, numerically. For moderate initial angles (from the frontal plane) and angular velocities of the thigh and shank, the pendulum exhibits motion closely resembling natural human gait. The results for all nationalities considered are very close to each other. For comparatively slow walking speeds, the model provides realistic results. Conclusions. Our approach highlights how a relatively simple biomechanical model can capture essential features of human locomotion and provides a foundation for further refinement and comparison with more complex gait modelling techniques. Such modifications are outlined.

Biomechanics doi: 10.3390/biomechanics6020041

Authors: Andreas Bourantanis Weijie Wang

Background: Ancient depictions of Pankration techniques have traditionally been interpreted through qualitative comparison with modern combat sports, without systematic biomechanical evaluation. The present study examines whether postural configurations derived from archeological artifacts are geometrically compatible with a continuous sagittal-plane trajectory under constrained inverse kinematics. Methods: A reduced planar humanoid model with three active rotational degrees of freedom was implemented in MATLAB Simulink(2024b), and artifact-derived initial and terminal postures were treated as boundary conditions. An analytical inverse kinematics solution was used to generate a continuous end-effector trajectory, from which joint kinematics and center-of-gravity displacement were computed. Motion capture data from ten participants were used solely to assess whether the generated trajectory is physically executable within human joint limits. Results: The results demonstrated strong agreement in selected local horizontal joint trajectories, while larger discrepancies were observed in vertical motion and global center-of-gravity behavior, reflecting the limitations of the reduced model. Conclusions: The study provides a reproducible framework for evaluating the kinematic feasibility of artifact-derived movements under explicitly defined constraints, limited to the assessment of geometric compatibility and physical executability.

Biomechanics doi: 10.3390/biomechanics6020040

Authors: Rodrigo Villaseca-Vicuña Pablo Merino-Muñoz John Cursach Natalia Escobar Guillermo Cortes-Rocco Felipe Inostroza-Ríos Felipe Hermosilla-Palma Jorge Perez-Contreras

Objective: To analyze the relationship between weekly accumulated external load and pre-match neuromuscular performance assessed through the countermovement jump (CMJ), in under-21 (U21) football players across 10 competitive microcycles. Methods: Sixteen U21 football players (age: 18.9 ± 0.42 years; height: 180 ± 6.3 cm; body mass: 78.5 ± 8.5 kg) from a Chilean professional club were monitored over 10 consecutive weeks. In each microcycle, the relationship between changes in neuromuscular performance estimated from CMJ-derived variables and two components of external load was analyzed: (1) weekly accumulated external load and (2) the acute–chronic workload ratio (ACWR). External load variables included total distance (TD), high-speed running distance (HSR), accelerations (ACC), decelerations (DC), and PlayerLoad (PL). CMJ variables included jump height (JH), modified reactive strength index (RSI-mod), and peak eccentric velocity (PEV). Performance changes were calculated as the percentage change (Δ%) between MD + 2 (start of the microcycle) and MD − 1 (pre-match). Pearson or Spearman correlation coefficients were applied depending on data distribution. Results: Significant negative associations were observed between weekly accumulated external load and changes in CMJ performance. Reductions in JH were associated with TD, HSR, ACC, and PL. Similar patterns were found for RSI-mod, while PEV showed a particularly strong association with ACC. Additionally, ACWR demonstrated significant negative relationships with CMJ changes, especially for HSR, ACC, and PL. Conclusions: Higher weekly accumulated external loads and elevated ACWR, particularly in high-intensity metrics such as high-speed running and accelerations, are associated with impaired pre-match neuromuscular performance. Consequently, monitoring CMJ-derived variables alongside external load data is recommended to manage fatigue and optimize match readiness in young football players.

Biomechanics doi: 10.3390/biomechanics6020039

Authors: Kento Sabashi Ryo Ueno

Background/Objectives: The Gait Variable Score (GVS) and Gait Abnormality Score (GAS) have been proposed as methods for quantitatively evaluating deviations from normal gait patterns. This study aimed to investigate whether the GVS or GAS is more useful for evaluating gait in stroke survivors. Methods: We used open-access motion capture datasets from 43 stroke survivors and 82 healthy individuals. Nine kinematics and seven muscle activities were extracted. The GVS was calculated as the root mean square difference between the pathological and healthy gait patterns. The modified GAS (mGAS) newly defined in this study was calculated as the mean value of the absolute differences between the pathological and healthy gait patterns divided by the standard deviation of healthy gait patterns. The amplitudes of kinematics and muscle activities were calculated. Results: Both the GVS and mGAS were significantly higher in stroke survivors than in healthy individuals. A significant strong correlation for 16 variables (nine kinematics and seven muscle activities) was observed between the GVS and amplitude (r = 0.921), but no significant correlation was found between the mGAS and amplitude (r = 0.167). Conclusions: As the mGAS is not affected by the amplitude of kinematics and muscle activities, it allows for a comprehensive comparison of abnormalities in both kinematics and muscle activities. The mGAS may be more useful than the GVS for evaluating gait abnormalities in stroke survivors.

Biomechanics doi: 10.3390/biomechanics6020038

Authors: Mehran Hatamzadeh Karolina Sowa Raphaël Dumas Adam Ciszkiewicz

Background: Multibody models are essential for studying knee joint mechanics, but their reliability and subsequent clinical utility are limited by uncertainties in ligament and contact parameters. Currently, no consensus exists on which parameters to prioritize or which statistical distributions best establish model credibility. Objectives: This scoping review aims to systematize reported uncertainty values for ligament and contact parameters in multibody models of the natural knee to identify trends and research gaps. Methods: Following PRISMA-ScR guidelines, a systematic search was conducted across PubMed, Scopus, and Web of Science. Methodological quality was assessed using a customized 13-item checklist, and the data were synthesized via a narrative approach by charting parameter types, quantification methods, and model structures. Results: In total, 19 articles were included (out of 494 identified), showing a wide variability in uncertain parameter types, values, and modeling approaches. Ligaments were typically represented as deformable cables with quadratic–linear behavior, while articular contact utilized elastic foundation formulations or mechanisms. Standard deviations of 30% of the mean for ligament stiffness and 0.02 for reference strain (typically modeled within Gaussian distributions) were the most frequently quantified uncertain parameters. Geometric uncertainties for ligament attachment points varied widely, ranging from 1.0 to 5.0 mm. Idealized contact geometry also varied within 2.5 mm for linear coordinates and 15° for angular coordinates. Conclusions: Wide variability and inconsistent reports highlight a need for standardized definitions of parameter uncertainty in multibody knee modeling to improve reproducibility of musculoskeletal knee simulations and ensure a reliable transition of these models into clinical practice.

Biomechanics doi: 10.3390/biomechanics6020037

Authors: Ann N. Reyes Timothy R. DeWitt Reuben H. Kraft

Background/Objectives: This paper investigates the application of radial basis function (RBF) interpolation to adapt the Toyota Human Model for Safety (THUMS) version 6 finite element (FE) models to diverse anthropometric profiles using ANSUR II data. The research focuses on generating personalized human body models (HBMs) across 50th, 80th, and 98th percentiles for both sexes in standing and seated postures, evaluating mesh quality with quantitative metrics, and assessing posture-dependent transformations. Methods: The geometric accuracy for the standing configuration was quantified using DICE similarity coefficients and the 95th percentile Hausdorff distance (HD95). Results: While global whole-body DICE similarity averaged approximately 0.40 due to an inherent variability in distal limb positioning, regional analysis demonstrated strong volumetric overlap in the critical chest and torso regions with DICE values ranging from 0.80 to 0.88. Regional HD95 values were within 20–30 mm across most of the surface area. Surfaces distance analyses showed that more than 95% of the nodes were within ±20 mm of the target surfaces with the distribution centered near zero across all the percentiles. The mesh quality for both standing and seated morphs demonstrated low violation rates with the aspect ratio being 28% to 30%, while warpage, skewness and, Jacobian determinants were less than 15%. The seated morphs preserved anatomical alignment and posture despite mesh density differences between the postures. Conclusions: These findings indicate that the morphing process preserves anatomical fidelity while highlighting the need for further optimization to mitigate localized distortions in dynamic simulations.

Biomechanics doi: 10.3390/biomechanics6020036

Authors: Maria J. Van Der Sandt Marta L. Machado Catarina C. Santos Mário J. Costa

Background/Objectives: Biomechanical research in surfing provides important insights into performance optimization and injury prevention, but the evidence remains fragmented across multiple domains. Methods: This scoping review aimed to systematically organize the existing literature on surfing biomechanics and evaluate the quality of the included studies. Searches were conducted by two independent reviewers in PubMed, Scopus, and Web of Science in accordance with the PRISMA Extension for Scoping Reviews. Systematic searches were performed up to 31 July 2025 using Boolean operators guided by the PECO framework. Methodological quality was assessed using the Downs and Black Quality Assessment Checklist. Results: Of the 195 records identified, 53 duplicates were removed. Following screening and fulltext review, 26 studies were included. Five studies employed randomized controlled designs, while 21 were non-randomized. Publications ranged from 2010 to 2025, with the majority conducted in Australia (65.4%). A total of 490 healthy surfers (mean age: 22.9 ± 16.1 years) were analyzed, with sample sizes ranging from 6 to 42 participants. Research topics included anthropometry, paddling biomechanics, aerial maneuvers, core and trunk strength and mobility, lower-limb function, frontside bottom turns, and pop-up performance. The studies’ methodological quality score was 11.7 points with substantial inter-reviewer agreement (κ = 0.77). Research on surf biomechanics remains limited in volume and exhibits methodological heterogeneity. Conclusions: Although existing studies provide valuable insights into key performance actions, further high-quality and standardized research on performance phases (e.g., paddling, pop-up, turns, aerials) and with different research designs (e.g., longitudinal, sex inclusive, ecological designs integrating lab and in-water measures) is needed.

Biomechanics doi: 10.3390/biomechanics6020035

Authors: Luca Puce Marco Panascì Gennaro Apollaro Vittoria Ferrando Piero Ruggeri Emanuela Luisa Faelli

Objective: The effects of fatigue on swimming propulsion are unclear. This study examined upper-limb propulsive force and bilateral coordination during constant-speed front crawl performed until exhaustion. Methods: Twelve competitive swimmers completed a visually paced front-crawl trial performed at a constant speed (95% of maximal speed) until volitional exhaustion. Upper-limb propulsion (pressure-derived) was quantified using wearable differential-pressure mini-paddles synchronized with high-speed video. Propulsive force and impulse were analyzed at ten standardized time points (10–100% of test duration), distinguishing the early (entry–catch–pull) phase and the push phase of the stroke cycle. Results: Total overall propulsive impulse (time-integral of propulsive force) and mean propulsive force decreased significantly as early as 30–40% of test duration, with the largest reductions occurring during the push phase. Interestingly, push-phase impulse declined earlier in the non-dominant left arm (from 20% of test duration) compared to the dominant right arm (from 40%), whereas force generated during the early phase did not change. Peak propulsive force decreased at later stages, while intra-cycle timing indices (peak timing and force centroid) and inter-limb asymmetry remained unchanged. Stroke frequency increased from mid-test onward and was strongly negatively associated with stroke efficiency (r = −0.79). Stroke efficiency correlated positively with push-phase impulse and peak force. Conclusions: During constant-speed front crawl performed to exhaustion, propulsion progressively declines, primarily through reduced force and impulse during the push phase rather than changes in the early (entry–catch–pull) phase or temporal and asymmetry-related variables. Increased stroke frequency initially compensates for declining propulsion but ultimately fails to maintain the imposed swimming velocity.

Biomechanics doi: 10.3390/biomechanics6020034

Authors: Konstantinos Thomas Kaliarntas Nelson Morais Georgios Andronikos Despoina Myrto Dounavi Athanasios Souglis Scott Wearing Gregory C. Bogdanis

Background: We assessed the effects of a 6-week, low-volume Nordic hamstring exercise (NHE) intervention on hamstring flexibility, muscle mechanical properties and eccentric and isometric isokinetic knee flexion strength in recreationally active adults. Methods: Eighteen recreationally active adults were randomized into an NHE intervention group (IG; n = 9; females/males: 3/6; mean ± SD, age: 24.1 ± 1.3 years) and control group (CG; n = 9; females/males: 5/4; mean ± SD, age: 23.5 ± 1.8 years). The NHE intervention involved a progressive, supplementary training program performed initially one (weeks 1 and 2) and then two times per week over a 6-week period. The number of repetitions per session increased from 15 to 36 repetitions/week. The CG maintained their usual exercise routine over the same period. Standard goniometry, myotonometry, and isokinetic dynamometry (60°/s) were used to measure hamstring flexibility, muscle properties and isometric and eccentric isokinetic strength prior to and five days following the intervention. Results: The Linear Mixed Methods analysis identified a significant group × time interactions for isometric torque (IG: +5% vs. CG: −12%, p = 0.022) and flexibility (IG: +1% vs. CG: +7%, p = 0.023). Peak eccentric torque (IG: +7% vs. CG: −7%, p = 0.053) and muscle mechanical properties remained unchanged over the intervention period. Conclusions: Six weeks of low-volume NHE training marginally improved isometric and eccentric hamstring strength in recreationally active adults without changing hamstring flexibility or mechanical properties. The findings may have important implications for performance enhancement and hamstring injury risk reduction during high-intensity recreational sports.

Biomechanics doi: 10.3390/biomechanics6020033

Authors: Arianna Fogliata Lorenzo Cantoni Alessio Gambetta Antinea Ambretti Stefano Tardini

Background/Objectives: Traditional biomechanical models describe human locomotion as an articulated chain of rigid segments with constrained degrees of freedom, primarily focusing on kinematic descriptions of movement. While this approach facilitates modelling and teaching, it may limit the representation of internal force transmission and dynamic interactions, particularly during transitional phases such as gait initiation. The objective of this article is to propose a conceptual framework, Unconstrained Segmental Biomechanics (USB), to reinterpret locomotor mechanics beyond rigid joint assumptions. Methods: An exploratory analysis of recent PubMed-indexed publications (2024) and commonly adopted educational references in sport science institutions was conducted to examine how locomotion is conceptually represented and to identify possible models analogous to the framework. The aim was to situate the framework within current modelling approaches rather than to provide a systematic literature evaluation. Results: The exploratory analysis provided an exploratory contextual impression that kinematic representations were more readily identifiable than conceptually analogous models explicitly addressing dynamic intersegmental force transmission. USB is presented as a conceptual framework generating testable biomechanical hypotheses concerning the temporal organisation of intersegmental force transmission during locomotor transitions, including the expectation that during gait initiation gluteus maximus activation precedes observable segmental displacement, that early CoP/GRF changes precede the visible step, and that trunk activation actively contributes to intersegmental force regulation during the transition. Conclusions: USB offers a conceptual framework that enriches the interpretation of gait initiation and locomotor transitions. Future empirical investigations will be necessary to test the biomechanical hypotheses generated by this framework and to evaluate its potential contribution to biomechanics research, education, and applied movement sciences.

Biomechanics doi: 10.3390/biomechanics6020032

Authors: Mariya Odrinskaya Elizaveta Strelkova Anastasia Rebik Pavel Aleksandrov Inna Midzyanovskaya

Background/Objectives: The vibrotactile system, which is essential for guiding behavior in nocturnal rodents such as mice and rats, provides critical sensory input. To investigate the role of vibrotactile sensory inflow in neonatal locomotion, we used previsual rat pups that underwent bilateral vibrissectomy. Subsequently, their motor behavior was evaluated in an open field test. Methods: A total of 42 previsual pups from four litters were assigned to either bilateral vibrissectomy or sham surgery groups on postnatal days (PND) 9–12, with group allocation balanced across litters. Results: Open-field testing on PND 13 revealed that while vibrissectomy (VE) did not affect gross locomotor activity—such as distance traveled, speed, acceleration, or freezing episodes (all >0.05)—it significantly altered spatial behavior. To quantify spatial patterns of curvy tracks, we analyzed trajectorial compaction within the central zone, lacking the tactile guidance of the walls: trajectories were smoothed using virtual coatings scaled to the vibrissal length (16 mm). For each track, an individual linearized reference path was generated and subjected to identical smoothing. The compaction ratio—calculated as the coated area of the smoothed linearized reference divided by the coated area of the experimental track—was significantly greater in VE pups than in sham controls (p = 0.03). This effect was not attributable to differences in the path length traveled within the central zone. The increased compaction persisted when the smoothing scale was increased 2–3 fold (32–64 mm radii, approximating the pups’ mean body size), but not at smaller scales (2–4 mm). Conclusions: These results demonstrate that tactile input specifically modulates the spatial, rather than locomotor, components of nonvisual navigation. Consequently, the track compaction may serve as a sensitive marker for assessing vibrotactile function in developing laboratory rodents.

Biomechanics doi: 10.3390/biomechanics6010031

Authors: Sara Mahmoudzadeh Khalili Feng Yang

Background: Falls are a leading cause of injury and mortality worldwide. Higher physical activity levels in young adults may increase exposure to fall-related situations. Understanding their neuromuscular adaptations is critical for balance control research and perturbation-based training. This study examined proactive and reactive adaptations in lower-limb muscle activity during repeated simulated trips among young adults. Methods: Twenty participants experienced five treadmill-induced standing-trips. Bilateral electromyography (EMG) activities of the rectus femoris (RF), vastus lateralis (VL), tibialis anterior (TA), medial gastrocnemius (MG), and biceps femoris (BF) were recorded. Muscle activity magnitude at perturbation onset (ON), EMG peak amplitude, and time-to-peak from ON were extracted and compared across trials. Results: Proactive activation at ON increased across trials in TA and RF on the recovery side (p = 0.012–0.023) and in TA, VL, and BF on the stance side (p = 0.002–0.034). Reactive peak amplitudes decreased in RF, VL, and BF on the recovery side (p < 0.001–0.014) and in RF, VL, and BF on the stance side (p < 0.001–0.016). Time-to-peak shortened in MG, RF, VL, and BF on the recovery side (p < 0.001–0.030) and in RF, VL, TA, and BF on the stance side (p < 0.001–0.050). Conclusions: Repeated simulated trips elicited proactive adaptations in muscle activity and reactive changes in time-to-peak, which may suppress the need for increased reactive muscle activations to recover balance post-perturbation over trials in young adults. The findings augment our understanding of the intercorrelation between proactive and reactive adaptations to repeated perturbations.

Biomechanics doi: 10.3390/biomechanics6010030

Authors: Lukáš Karabin Jozef Sýkora Roman Švantner Kevin R. Ford Martin Pupiš Tomas Maly

Objectives: This study compares linear sprint force–velocity (F–v) mechanical variables between elite Under-19 (U19) academy players and senior professional players. Methods: Thirty-eight senior players (SP; mean age 24.5 ± 4.3 y) and 214 U19 academy players (YP; mean age 17.4 ± 0.5 y) from 14 first-division club academies were tested during October 2023 using a motorized resistance device (1080 Motion). The following F–v variables were assessed: maximal theoretical force (F0, N·kg−1), maximal theoretical velocity (v0, m·s−1), maximal ratio of horizontal-to-resultant force (RFmax, %), and decrease in the ratio of forces (DRF, %). Between-group comparisons were performed using the t-test, and Cohen’s d effect sizes were reported. Results: Senior players outperformed U19 players across all F–v variables. F0 exhibited a mean difference = 0.220 N·kg−1, with a 95% confidence interval (CI) [0.056, 0.384], p = 0.0166, and d = 0.46. v0 exhibited a mean difference = 0.560 m·s−1, with a 95% CI [0.410, 0.710], p < 0.0001, and d = 1.07. RFmax exhibited a mean difference = 1.470%, with 95% CI [0.830, 2.110], p = 0.0003, and d = 0.69. DRF exhibited a mean difference = 0.260%, with a 95% CI [0.103, 0.417], p = 0.0013, and d = 0.53. Conclusions: U19 players demonstrated lower F0, lower v0, and reduced mechanical effectiveness compared with senior players. Regular monitoring of F–v profiles and individualized training interventions (force- or velocity-targeted) may be useful for training and monitoring strategies aimed at supporting physical preparation during the transition to senior soccer.

Biomechanics doi: 10.3390/biomechanics6010029

Authors: Masoud Abedinifar Şenay Mihçin Mehmet Yılmaz

Background/Objectives: Quasi-static inverse dynamics is widely used in biomechanical analyses due to its computational simplicity; however, neglecting inertial effects may introduce joint-specific torque estimation errors during dynamic movements. The purpose of this study was to quantify torque estimation errors introduced by quasi-static assumptions during bodyweight squats performed at different movement frequencies. Methods: A planar MATLAB-based (version R2022a) musculoskeletal model incorporating standard anthropometric parameters was developed to simulate squat motions at 1.00, 0.75, 0.50, and 0.25 Hz. Joint torques calculated using quasi-static inverse dynamics were compared with fully dynamic inverse dynamics at the ankle, knee, and hip. Model agreement was evaluated using Root Mean Square Error (RMSE), normalized percentage error relative to peak dynamic torque, and bootstrapped 95% confidence intervals (CI). Results: Quasi-static modeling produced negligible torque estimation errors at the ankle and knee across all movement frequencies, with percentage errors consistently below 0.1% and narrow confidence intervals. In contrast, the hip joint demonstrated a clear frequency-dependent underestimation of torque when inertial effects were neglected. At 1.00 Hz, the hip RMSE reached 14.4 Nm, corresponding to 14.01% of peak dynamic torque (95% CI: 13.97–14.06%). Error magnitude increased systematically with movement speed. Conclusions: The validity of quasi-static inverse dynamics strongly depends on joint location and movement frequency. While quasi-static models are appropriate for ankle and knee torque estimation during moderate-speed squats, accurate hip torque assessment during faster squats requires full dynamic modeling. These findings provide quantitative benchmarks to inform model selection in biomechanical research, rehabilitation engineering, and assistive device design.

Biomechanics doi: 10.3390/biomechanics6010028

Authors: Tomoki Yamamoto Yu Kashiwagi Takafumi Kageyuki Fumiaki Kobayashi Kazuo Funato

Background/Objectives: In pole vaulting, the capacity to store elastic energy within the pole (Epole) significantly influences performance. This study investigated the characteristics of Epole storage by analyzing the box reaction force and vector angle. Methods: Eight male pole vaulters, including World Championships participants, were examined. A motion capture system (VICON) and force plates (Kistler) were used to measure the vector angle (angle between the compression force (CF) and box reaction force vectors) and horizontal velocity of the center of gravity (COG) (Vcogh). Epole was calculated as the integral of the CF (estimated from the box reaction forces), and pole bending displacement. The relationships between each variable and the peak height of COG (HP) were assessed using Pearson’s product–moment correlation coefficients. Results: HP correlated with Vcogh in the pole plant (PP) (r = 0.82) and Epole (r = 0.94). Vaulters with a higher HP maintained a vector angle < 2° between 20% and 80% of the pole bending phase, indicating closer directional alignment between the box reaction force vector and pole chord direction, whereas vaulters with lower HP exhibited larger vector angles (4–8°), associated with a relative reduction in the axial component of force transmitted to the pole. Conclusions: A smaller vector angle effectively enhanced the CF, thereby increasing pole bending and promoting greater accumulation of Epole. Therefore, maintaining a small vector angle may enable more effective force transmission along the pole chord, and vector angle characteristics and PP horizontal velocity may assist appropriate pole selection and training strategies to enhance elastic energy storage and performance.

Biomechanics doi: 10.3390/biomechanics6010027

Authors: Bushira Musa Ji Chen Glacia Martin Kaitlin H. Lostroscio Alexander Peebles

Background: Microgravity exposure causes muscle atrophy and bone density loss in astronauts. Traditional motion analysis provides estimations of external kinematics and muscle activation, but cannot resolve internal load. OpenSim closes this gap by applying musculoskeletal modeling to estimate internal joint mechanics. Methods: In this study, we aimed to develop an OpenSim workflow to estimate joint angles and moments using datasets from two publicly available gait studies: the Politecnico di Milano study (Dataset 1), which includes level-floor walking, walking on heels, walking on toes, and step-down-from-stairs tasks, and Maclean et al.’s walking study in reduced gravities (Dataset 2), which includes four simulated gravity levels (1.0 G, 0.76 G, 0.54 G, and 0.31 G). Marker and ground reaction force (GRF) data, along with participants’ mass, were used to prepare the first three steps of OpenSim’s workflow, including scaling, inverse kinematics (IK), and inverse dynamics (ID). Scripts using MATLAB R2025a (The MathWorks, Inc., Natick, MA, USA) were created to store, normalize, and compare OpenSim outputs with reference data on the right leg. Pearson’s correlation coefficient (PCC) was used to quantify agreement between OpenSim-derived joint angles and moments and the reference data, and root mean square error (RMSE) was used to characterize accuracy. Results: Hip and knee angles showed excellent correlation across both datasets (PCC > 0.974). Ankle angles were more variable, particularly in Dataset 1 (PCC = 0.833; RMSE = 19.797°) compared to Dataset 2 (PCC = 0.995; RMSE = 8.73°). Joint moment correlations were strong for hip and knee (PCC > 0.85), though ankle moments in Dataset 1 exhibited lower correlation (PCC = 0.677) and higher error (0.30 Nm/kg) compared to the high accuracy observed across all joints in Dataset 2. Discussion: We speculate that the lower PCC values and higher RMSE observed for ankle dorsi/plantar flexion angle and moment in Dataset 1 are mainly attributable to differences in shank segment frame definitions between the OpenSim model and the human body model used in Dataset 1. Higher ankle angle RMSEs in Dataset 2 may be due to lower weights assigned to ankle markers in the scaling and IK setup files, resulting in different ankle joint center definitions. Conclusion: In the future, we plan to improve this OpenSim workflow by including additional participants and datasets collected in simulated reduced-gravity environments and by implementing a residual reduction algorithm (RRA) and computed muscle control (CMC) to enable muscle activation estimation.

Biomechanics doi: 10.3390/biomechanics6010026

Authors: Ivan Curovic Milan Markovic Lazar Toskic Jill Alexander Damian J. Harper

Background/Objectives: To evaluate the intraday and interday reliability of seated horizontal upper body (UB) isometric push and pull tests performed with the VALD DynaMo Max dynamometer. Methods: Fifty-two recreationally active individuals (41 men, 11 women; 25.0 ± 6.1 years) completed two sessions 48 h apart, each comprising three maximal-effort push and pull trials at 90° elbow flexion using a custom-built rig with the attached dynamometer. Peak force (PF), peak rate of force development (RFD), impulse, and time-to-PF were extracted from 1200 Hz force–time data. Reliability was assessed using the intraclass correlation coefficient (ICC), coefficient of variation (CV%), standard error of measure (SEM) and minimal detectable change (MDC). Results: PF demonstrated excellent reliability (ICC = 0.97–0.99) with low absolute error (CV < 6%; MDC = 128–149 N). Impulse showed good-to-excellent reliability (ICC = 0.90–0.94; CV < 10%; MDC ≈ 755–790 N·s), whereas RFD displayed good reliability but greater variability (ICC = 0.80–0.81; CV < 20%; MDC = 2574–2925 N·s−1). Time-to-PF was the least reliable (ICC = 0.68–0.71; CV > 24%; MDC = 1.5–1.7 s). Conclusions: Horizontal isometric push and pull tests using the VALD DynaMo Max dynamometer provide reliable measures of PF and impulse for athlete profiling and tracking substantial longitudinal changes. Peak RFD may be cautiously used for broad cross-sectional comparisons, although its higher variability limits precision in distinguishing smaller inter-individual differences and appears less sensitive to within-individual changes. Time-to-PF demonstrated insufficient reliability for practical application.

Biomechanics doi: 10.3390/biomechanics6010025

Authors: Anna Chalkia Eleftherios Paraskevopoulos Dimitris Mandalidis

Background/Objectives: Emerging evidence suggests the presence of associations in joint mobility along anatomically defined myofascial continuities, indicating that joint mobility may co-vary across anatomically distant regions. This study aimed to investigate the correlations between the active range of motion (ROM) of joints belonging to the same myofascial chain in healthy, physically active individuals. Methods: Active ROM was measured in 61 adults (21 males and 40 females) at joints contributing to four myofascial chains: the superficial front line (SFL), superficial back line (SBL), functional front line (FFL), and functional back line (FBL), using an inertial measurement unit. Partial Pearson’s correlation coefficients (r), controlling for sex, were calculated to examine the relationships between joint ROM values within lines, with statistical corrections applied when necessary. Results: Significant, yet weak to moderate in most cases, partial correlation coefficients were identified among joints in the upper SFL (0.32–0.44), the lower SBL (0.42–0.44), along the FFL (0.29–0.51), and between the lower segments of the BFL (0.48–0.60). Conclusions: While some joint ROMs within myofascial chains demonstrate weak-to-strong associations, overall interdependence appears mode- and region-specific. These findings suggest that factors beyond fascial continuity, such as neuromuscular control, joint structure, and movement habits, are likely to contribute to ROM variability.

Biomechanics doi: 10.3390/biomechanics6010024

Authors: Filip Hruša Petr Kubový František Lopot Luboš Tomšovský Karel Jelen

Background: Alpine skiing imposes high biomechanical demands on the lower limbs, which are further amplified in individuals with transfemoral amputation due to prosthetic constraints. This study aimed to quantify three-dimensional knee flexion asymmetries during alpine skiing turns in transfemoral amputee skiers compared with non-disabled controls. Methods: Five unilateral transfemoral amputee skiers (intervention group) and five non-disabled ski instructors (control group) performed six left and six right turns on a skiing simulator under laboratory conditions. Knee flexion angles at the apex of each turn were analyzed using three-dimensional motion capture. Intra-individual differences between the prosthetic and intact limbs were assessed using paired comparisons, and inter-individual differences between groups were evaluated using independent statistical tests (p < 0.05), performed in IBM SPSS Statistics. Results: Intra-individual analysis revealed significant knee flexion asymmetries (p < 0.05) in almost all amputee participants at the apex of both left (mean difference = 7.74°, 95% CI: 3.38–12.09) and right turns (mean difference = 4.36°, 95% CI: 2.66–6.06). In the control group, asymmetries were smaller and reached significance only for the inside leg in both turns (mean difference = 4.02°, 95% CI: 2.51–5.54). Inter-individual comparisons demonstrated significant differences between the groups for both turning directions. During left turns (prosthetic limb on the inside), the largest difference was observed for the inside leg (26.9°, p < 0.001), while the smallest difference occurred for the outside leg (12.1°, p = 0.013). During right turns (prosthetic limb on the outside), the largest difference was found for the outside leg (19.0°, p < 0.001), with a smaller but still significant difference for the inside leg (14.0°, p < 0.001). Conclusions: Transfemoral amputee skiers exhibit a turning strategy that is qualitatively comparable to that of non-disabled skiers; however, it is characterized by a reduced knee flexion range of motion. These limitations appear to be primarily influenced by prosthesis mechanics and user-specific skill levels rather than by a fundamentally different movement strategy.

Biomechanics doi: 10.3390/biomechanics6010023

Authors: Eranga Bandara Ross Gore Sachin Shetty Ravi Mukkamala Christopher K. Rhea Brittany S. Samulski Amin Hass Atmaram Yarlagadda Shaifali Kaushik Malith De Silva Andriy Maznychenko Inna Sokolowska Kasun De Zoysa

Background/Objectives: Accurate assessment of neuromuscular reflexes, such as the Hoffmann reflex (H-reflex), plays a critical role in sports science, rehabilitation, and clinical neurology. Conventional interpretation of H-reflex electromyography (EMG) waveforms is subject to inter-rater variability and interpretive bias, limiting reliability and standardization. This study aims to develop an automated, interpretable, and robust agentic AI–driven framework for H-reflex waveform analysis. Methods: We propose a fine-tuned Vision–Language Model (VLM) consortium combined with a reasoning Large Language Model (LLM)–enabled decision support system for automated H-reflex interpretation. Multiple VLMs were fine-tuned on curated datasets of H-reflex EMG waveform images annotated with expert clinical observations, recovery timelines, and athlete metadata. The VLM outputs were aggregated using a consensus-based strategy and further refined by a specialized reasoning LLM to ensure coherent, transparent, and explainable diagnostic assessments. Model fine-tuning employed Low-Rank Adaptation (LoRA) and 4-bit quantization to enable efficient deployment on consumer-grade hardware. Results: Experimental evaluation demonstrated that the proposed hybrid system delivers accurate, consistent, and clinically interpretable assessments of neuromuscular states, including fatigue, injury, and recovery, directly from EMG waveform images and contextual metadata. Compared with baseline models, the fine-tuned VLM consortium exhibited substantially improved precision, consistency, and contextual awareness, while the reasoning LLM enhanced diagnostic coherence through cross-model consensus and structured reasoning, thereby supporting responsible and explainable AI-driven decision making. Conclusions: This work presents, to the authors’ knowledge, the first integration of a responsible and explainable AI-driven decision support system for H-reflex analysis. The proposed framework advances the automation and standardization of neuromuscular diagnostics and establishes a foundation for next-generation AI-assisted decision support systems in sports performance monitoring, rehabilitation, and clinical neurophysiology.

Biomechanics doi: 10.3390/biomechanics6010022

Authors: Kazuhito Yanabashi Koji Moriya Yutaka Maki Takuya Yoda Hiroshi Hatano Hiroyuki Kawashima

Background/Objectives: Polyaxial locking systems for distal radius plates differ among manufacturers, and the mechanical strength of their locking mechanism is rarely disclosed. This study aimed to perform a preliminary mechanical evaluation of a newly developed polyaxial locking mechanism and to investigate its strength at different screw insertion angles. Methods: The polyaxial locking mechanism was evaluated via static load testing at three screw insertion angles until failure, and the maximum bending moment was measured. Loading was performed via cantilever bending to generate a bending moment in the polyaxial locking mechanism. The maximum bending moments of the insertion angles of 10° for the holes in the distal rows were investigated for significant differences. Results: Maximum bending moments significantly decreased as the screw insertion angle increased, with reductions of approximately 50% at 5° and 10° compared with 0°. At a 10° insertion angle, variation in ultimate strength was observed among screw hole in the distal row. The failure mechanism was loosening of the locking screws in all tests. Conclusions: The maximum bending moment of the polyaxial locking mechanism decreased with increasing locking screw insertion angle, highlighting the importance of insertion angle in polyaxial locking plate fixation.

Biomechanics doi: 10.3390/biomechanics6010021

Authors: Rachel Ward Roger O. Kollock Madeleine Fulk Zora Szabo Maddie Dugan Muhammad O. Malik Jacob Thomas Greysee Floyd Gabe J. Sanders

Background/Objectives: Musculoskeletal injuries (MSIs) continue to be a significant challenge in military populations. Load carriage is cited as a key contributor to postural stability (PS) impairments and therefore may contribute to injury risk. Therefore, the purpose of the present study was to examine the influence of load per kilogram of body mass (LpBM) on dynamic postural stability index (DPSI) percentage difference between unloaded and loaded conditions, while moderating for biological sex. Methods: Thirty-three recreationally active adults (16 males, 17 females) participated in a cross-sectional study. Each participant performed single-leg landing (SLL) tasks under unloaded and loaded conditions, and DPSI was calculated using ground reaction force data collected over the first three seconds post-landing. The loaded condition (22–23 kg, varies based on helmet and vest size) required individuals to wear a full combat load. A moderated multiple regression with robust standard errors was run to determine whether the relationship between percentage difference in DPSI between unloaded and loaded conditions and LpBM carried is different for female and male participants. Results: There was not a statistically significant moderator effect of the DPSI percentage difference, as evidenced by the addition of the interaction term explaining an additional 0.94% of the total variance, p < 0.643. Follow-up standard multiple regressions revealed that there was a statistically significant positive linear relationship (0.887 ± 0.320) between DPSI percentage difference and LpBM (p = 0.010). It was also observed that females did not have statistically significantly higher DPSI percentage difference than males (1.210 ± 4.392, p = 0.785). Conclusions: The results suggest that as LpBM increases, stability becomes more difficult to maintain. These findings highlight the importance of considering relative load when assessing injury risk and designing load carriage training protocols in tactical populations.

Biomechanics doi: 10.3390/biomechanics6010020

Authors: Shihao Jia Tiev Miller Oliver Roberts Joshua Chan Tracy Ho Tsz-Hin Chan Patrick Wai-Hang Kwong

Background/Objectives: The calf muscles are vital for generating propulsive force during walking. This power is produced from calf muscle contractions and elastic strain energy release. However, the impact of walking speed on these power-generation mechanisms is understudied. This study aimed to investigate how different walking speeds affect calf muscle activation and ankle power generation. Methods: In this study, we analyzed electromyography (EMG) signals from the gastrocnemius (GAS) and soleus (SOL) muscles of 55 healthy individuals walking at various speeds. C1: household ambulators (0–0.4 m·s−1), C2: limited community ambulators (0.4–0.8 m·s−1), C3: community ambulators (0.8–1.2 m·s−1), C4: self-selected usual speed, and C5: self-selected fast speed. Results: Deviating from a participant’s self-chosen pace led to increased cumulative muscle activity and prolonged plantar flexor activation. Optimal muscle activation was observed at speeds between 0.8–1.2 m·s−1. A second-degree polynomial mixed model best captured the relationship between muscle activation duration and integrated EMG in the ankle power generation phase in late stance, demonstrating the nonlinear relationship between walking speed and calf muscle activation in this phase. Statistically significant models (p < 0.001) explained over 50% of the variability in GAS activation duration (R2 = 0.55) and integrated EMG (R2 = 0.56), as well as SOL activation duration (R2 = 0.52) and integrated EMG (R2 = 0.72). Conclusions: The nonlinear relationship between walking speed and calf muscle activation indicates that normal walking speed optimizes the utilization of elastic strain energy in the ankle power generation phase.

Biomechanics doi: 10.3390/biomechanics6010019

Authors: Manuel Nogueras Pablo Floria Amelia Ferro-Sánchez

Background/Objectives: In Rhythmic Gymnastics (RG), the jump is an element of great difficulty that requires the qualities of strength and coordination. Jump height and power are the variables normally used to assess the final performance of jumps. However, they do not allow us to analyze what happens in the intermediate stages or provide practical information to find jump improvement strategies. This study aimed to determine which kinetic variables, organized within a hierarchical model, serve as performance indicators in the Pike Jump executed from a standing start with arm swing. Methods: Ten high-level women gymnasts (14 ± 0.7 years) performed 53 Pike Jumps on a Dinascan-IBV, v.8.1 dynamometric platform (Valencia, Spain) that recorded at 1000 Hz. In the model, jumping was divided into five phases, and 76 related efficacy variables were defined, with 34 of them normalized for total jump time or body weight. Bivariate correlations were analyzed with a bilateral significance test to validate the proposed model. Results: Average and Initial Vertical Ground Reaction Force can be used as performance indicators of the Pike Jump, providing information on intermediate stages of the jump and allowing us to improve specific aspects related to the level of force and the way to apply it in RG. Conclusions: The degree of correlation found among the variables allowed us to validate the model. Normalized variables allow a more precise analysis to be carried out and question some results obtained in the literature in which non-normalized data were presented.

Biomechanics doi: 10.3390/biomechanics6010018

Authors: Zoey C. Kearns Rebecca L. Krupenevich Jason R. Franz Douglas W. Powell Max R. Paquette

Endurance running exposure alone may not be sufficient to slow the age-related decline in plantarflexor function, which is also thought to contribute to the decline in running economy. Strength training has been shown to improve running performance, but specific programs have not been evaluated for their assistance in maintaining plantarflexor function and “youthful” metabolic costs in aging runners. The purpose of this study was to assess the relative influence of three types of resistance training interventions on running economy (RE), plantarflexor function, and Achilles tendon (AT) stiffness in middle-aged runners. Methods: Twenty-six middle-aged runners (51 ± 5 yrs) participated in one of three 10-week resistance training interventions: (1) heavy resistance training, (2) heavy resistance training + plyometrics, and (3) endurance resistance training + plyometrics. Laboratory testing for RE, biomechanical variables, peak plantarflexor torque, and AT stiffness during isometric contractions occurred before and after the interventions. A mixed-design repeated measures ANOVA was used to address our research question, while paired and independent t-tests were used to compare time and group effects, respectively. Results: Relative (to V˙O2max) RE (−2.4%, p = 0.016), AT stiffness (+26.1%, p = 0.002), and peak isometric plantarflexor torque (+26.4%, p = 0.001) improved with resistance training, with no interaction or group effects. No significant interaction, time, or group effects were observed for V˙O2max and peak plantarflexor torque, peak positive ankle power, or positive and negative ankle work while running. Conclusions: We present novel but exploratory findings that resistance training, regardless of modality, may moderately improve RE and Achilles tendon stiffness in middle-aged recreational runners. However, sagittal plane lower joint kinematics, extensor torques, powers, and work were unaffected by resistance training in middle-aged runners.

Biomechanics doi: 10.3390/biomechanics6010017

Authors: Rute Vieira e Magalhães Rodrigues Beatriz Regina Legutke Gabriel Antonio Gazziero Moraca Thiago Martins Sirico Murilo Lorencetti Torres Diego Orcioli-Silva Victor Spiandor Beretta

Background/Objectives: People with Parkinson’s disease (PwPD) exhibit impairments in postural responses to perturbations, increasing their risk of falls. While transcranial direct current stimulation (tDCS) has been shown to enhance postural responses in PwPD, its effects considering history of falls remain unclear. Thus, we aimed to analyse the effect of tDCS on postural responses after external perturbation in PwPD with and without a history of falls. Methods: Twenty-two PwPD were distributed into two groups—faller (n = 12) and non-faller (n = 10)—based on their history of falls over the 12 months preceding the experiment. A 20 min anodal tDCS was applied to the primary motor cortex (M1) under two conditions (2 mA and sham), performed on two different visits (at least 2 weeks apart) with a randomised order. Seven trials with temporally unpredictable external perturbation (i.e., backward translation of the support base) were performed after tDCS. Electromyographic (i.e., medial gastrocnemius (MG) onset latency, magnitude of muscle activation of MG and tibialis anterior (TA), and MG/TA coactivation index) and centre of pressure (CoP) parameters (i.e., range of CoP, peak of CoP velocity, and recovery time) were analysed to assess postural response. A two-way ANOVA (Group × Stimulation Condition) was performed. Results: Both groups had shorter recovery time (determined by CoP) and MG onset latency in the active vs. sham condition. Conclusions: The results of our pilot study suggest that a single 20 min tDCS session (2 mA) applied over M1 enhances postural responses similarly in PwPD with and without a history of falls in the past year.

Biomechanics doi: 10.3390/biomechanics6010016

Authors: Zahra Mollaei Emily E. Gerstle Mohammed S. Alamri Stephen C. Cobb

Background: Older adult falls during step negotiation result in higher injury rates compared to level ground falls. Previous research on discrete events during step negotiations may not capture important age-related changes. Curve analysis techniques enable assessment of an entire time series and may further advance the understanding of older adult falls during step negotiation. The purpose of the current study was to investigate lower extremity kinematics during transition step negotiation in older women with fall history compared to young women using statistical parametric mapping (SPM). Methods: 15 older female adults with a fall history and 15 young female adults participated in the study. Participants performed walking trials along a 5.5 m raised walkway, descended a 17 cm step and continued walking 3 m. Data was processed from lead limb toe-off prior to the step, through lead limb weight acceptance of the transition step. SPM was used to perform independent t-test analysis of the three-dimensional lower extremity time series. Results: The older faller group showed significantly decreased lead hip abduction (9–19% of step negotiation, mean difference: 3.74°, p = 0.045), increased lead knee flexion (65–80% of step negotiation, mean difference: 5.8°, p = 0.012), and increased trail limb hip adduction (91–100% of step negotiation, mean difference: 3.92°, p = 0.046). Conclusions: The older faller group showed altered hip joint angles in the frontal plane and knee joint angles in the sagittal plane during early swing and late weight acceptance phases, which may reflect compensatory strategies for reduced strength and/or balance. Curve analysis provides additional insight into age-related kinematic changes during step negotiation that may be related to older adult fall risk.

Biomechanics doi: 10.3390/biomechanics6010015

Authors: Martin Grimmer Omid Mohseni Julian Seiler Maziar A. Sharbafi Rolf Findeisen Andre Seyfarth Mario Kupnik

Background/Objectives: This study investigated the biomechanics of a hip exoskeleton during sit-to-stand transitions. Methods: Eleven participants performed the task under three conditions: without the exoskeleton (No Exo), wearing the exoskeleton without assistance (Exo Off), and wearing it with hip extension assistance (Exo On). Results: The analyses revealed that joint angles (hip, knee, and ankle) and vertical ground reaction forces were comparable across all conditions. However, Exo Off significantly increased transition time, whereas Exo On did not differ significantly from No Exo. Additionally, both exoskeleton conditions led to increased integrated EMG (iEMG) activity in the rectus femoris, vastus medialis, and gluteus maximus—likely due to the added device mass. Notably, iEMG analysis revealed a significant reduction in gluteus maximus activity in Exo On compared to Exo Off. Conclusions: Despite providing only moderate torque assistance (0.12 Nm/kg), the results suggest that well-timed exoskeleton support can partially reduce the physical demands of sit-to-stand transitions. However, the observed reduction in gluteus maximus activity was limited, likely reflecting the combined effects of the assistance strategy, including its magnitude and timing, user adaptation and training, postural demands due to device weight and external torques, and mechanical constraints such as potential joint misalignment. Further research is needed to optimize hip exoskeleton support for daily activities.

Biomechanics doi: 10.3390/biomechanics6010014

Authors: Arunee Promsri Punnakan Pitiwattanakulchai Siwaporn Saodan Salinrat Thiwan

Background: The 1 min sit-to-stand test (1-MSTST) is a widely used functional assessment involving repetitive sit-to-stand transitions. This study examined local dynamic stability during the 1-MSTST across three acceleration directions, compared young and middle-aged women, and explored associations between body composition and stability. Methods: Twenty-four young adult women (24.1 ± 5.2 years) and twenty-four middle-aged women (51.4 ± 5.9 years) performed the 1-MSTST. Trunk accelerations were recorded using a tri-axial accelerometer at L5. Local dynamic stability was quantified using the largest Lyapunov exponent (LyE), and movement magnitude using root mean square (RMS). Directional, group, and correlational analyses were performed with correction for multiple testing. Results: Significant directional differences were observed for both LyE and RMS, with all pairwise contrasts between mediolateral (ML), anteroposterior (AP), and vertical (VT) directions remaining significant after correction (p < 0.001). Apparent age effects in LyE were no longer significant after adjusting for cadence, BMI, and multiple testing, indicating no robust age-related difference in local dynamic stability. Body fat percentage showed moderate positive correlations with LyE in the VT (p = 0.003) and AP (p = 0.003) directions. Muscle mass percentage showed a moderate positive correlation with VT LyE (p = 0.002) and moderate negative correlations with ML (p = 0.002) and AP LyE (p = 0.002). Conclusions: Stability during the 1-MSTST differs by direction, with the greatest variability in the mediolateral axis. No independent age effect was found. Higher body fat relates to poorer stability, while greater muscle mass supports better movement control.

Biomechanics doi: 10.3390/biomechanics6010013

Authors: Ashna Ghanbari Patrick Milner Sandro R. Nigg Matthew J. Jordan

Background/Objectives: Noncontact knee ligament injuries, including anterior cruciate ligament (ACL) ruptures and medial collateral ligament (MCL) sprains, are prevalent in sports that involve frequent cutting and pivoting. Conventional rigid knee braces can offer stability but often compromise comfort and performance, whereas soft sleeve-type supports provide minimal mechanical protection. The purpose of this study was to evaluate the acute biomechanical effects of a tensioned cable knee bracing system on peak knee valgus angle and external knee abduction moment during a controlled lateral shuffle task. Methods: Ten physically active adults (mean age 21.7 ± 3.8 years) performed submaximal lateral shuffle movements under three conditions: unbraced, sleeve-only (zero-tension), and a novel tensioned cable brace. Three-dimensional knee kinematics and ground reaction forces were collected, and peak knee valgus angle and external abduction moment were calculated during the eccentric phase of each movement. Results: Wearing the knee brace under tension significantly reduced knee valgus angle (4.5° vs. 7.9°) and peak external knee abduction moment (1.6 vs. 2.0–2.1 Nm/kg) compared to the unbraced condition. Conclusions: These findings indicate that the tensioned cable brace effectively reduced frontal plane knee loading during a lateral shuffle task, indicating its potential as an effective bracing approach.

Biomechanics doi: 10.3390/biomechanics6010012

Authors: Ricardo Pimenta Hugo Antunes Nuno Pimenta José Pedro Correia António Veloso

Objectives: The purpose of this study was to determine whether hamstrings’ passive and active shear moduli measured before and after a fatigue task are correlated. Studying the correlation between passive and active shear moduli is important because, if correlated, passive SWE could provide a quicker assessment without requiring fatigue-inducing voluntary contractions. Methods: Forty-seven football players with no history of hamstring strain injury participated. Muscle shear modulus was assessed only in the dominant lower-limb (dominance defined as the preferred kicking limb) using ultrasound-based shear wave elastography at rest and during isometric contractions at 20% of maximal voluntary isometric effort before and immediately after a 10 × 30 m repeated sprint protocol. Results: Regarding sprint performance, a significant decrease of 8.3% was seen between the first and the last sprints (first: 7.14 ± 0.27 m/s; last: 6.60 ± 0.31 m/s; p < 0.001; dz = 1.88 [1.40–2.35]). In relation to the peak torque normalized to bodyweight, a significant decrease of 9.2% was seen between pre and post (pre: 1.98 ± 0.30 Nm/kg; post: 1.83 ± 0.31 Nm/kg; p < 0.001; dz = 0.89 [0.78–0.95]). Regarding the correlation analysis, none of the passive and active shear moduli measures was significantly correlated in any condition (Bonferroni correction for multiple comparisons, significance threshold set at p < 0.004). Conclusions: The results suggest that the hamstrings’ passive and active shear moduli are not correlated after a fatigue task.

Biomechanics doi: 10.3390/biomechanics6010011

Authors: Gaël Bescond Céline De Passe Véronique Feipel Joe Abi Nader Fedor Moiseev Serge Van Sint Jan

Background/Objectives: Considering that the kinematics of the temporomandibular joints (TMJs) is concomitant with head movements and that temporomandibular joint disorders (TMDs) are frequently associated with neck pain in clinics but seldom or never investigated, the aim of this study was to develop a reliable in vivo measurement protocol of the simultaneous amplitudes of the mandible and of the skull. The development of such a protocol is part of a project to build an accurate kinematic assessment tool for clinicians in the orofacial field who treat patients suffering from TMD. Methods: Mouth opening, laterotrusion and protrusion movements for three different positions of the head (neutral, slouched and military) on 12 asymptomatic voluntary subjects (5 men and 7 women, mean 33.6 yo +/− 11.1) were recorded using 20 markers palpated and taped and 14 optoelectronic cameras. The acquisition frequency was set at 150 hertz. The inter- and intra-examiner reliability of marker palpation in mm was calculated using standard deviation (SD), mean difference (MD) and standard error (SE). Amplitudes of movement according to axes defined by the International Society of Biomechanics (ISB) are given for the mandible and skull segments. The propagation of error on the amplitudes was calculated with the root mean square propagation error (RMSPE) in degrees. Repeated-measures ANOVA or Friedman tests were used to assess the influence of the position of the head on the amplitudes of the jaw. Power analysis of the sample size was estimated with Cohen’s f3 size effect test. Steady-state plots (SSPs) and normalized motion graphs between the skull and the mandible motion were performed to study the coordination of their maximum amplitude over time. Results: The protocol demonstrated good intra-examiner reliability (1.5 < MD < 5.8; 2.6 < SD < 7.8; 2.0 < SE < 3.8), good inter-examiner reproducibility (0.2 < MD < 4.0; 3.5 < SD < 4.6; 2.0 < SE < 2.5) and small error propagation (0.0 < RMSPE intra < 2.8; 0.0 < RMSPE inter < 1.0). The amplitudes of the jaw and head found during the three types of movements correspond to the values reported in the literature. Head positions did not appear to significantly influence the amplitudes of jaw movements, which could be explained by the power estimation of our sample (Type II error β = 0.692). The participation of head movements in those of the jaw, for all motions and in all positions, was demonstrated and discussed in detail. Conclusions: The accuracy, test–retest reliability, and intra-individual variability of the TMJ kinematic analysis, including head movements, was ensured. The small sample size and the absence of standardized head positions for the subjects limit the scope of the intra- and inter-group analysis results. Given the natural biological and complex coordination of jaw–head movement, the authors consider its evaluation useful in clinical intervention and would like to further develop the present protocol. The next step should be to test the feasibility of its clinical application with a larger group of asymptomatic subjects compared to patients suffering from TMD.

Biomechanics doi: 10.3390/biomechanics6010010

Authors: Eirini Zanni Ioannis Stavridis Elias Zacharogiannis Prokopios Chatzakis Polyxeni Argeitaki Giorgos Paradisis

Background/Objectives: This study aimed to examine the post-activation performance enhancement effects of bilateral horizontal drop jumps (BHDJs) on 30 m sprint and countermovement jump (CMJ) performance, as well as in sprint mechanical and kinematics characteristics. Methods: Fourteen young sprinters (nine boys and five girls) completed both an experimental condition (EC) and a control condition (CC). The EC consisted of five BHDJs performed at each participant’s individually determined optimal drop height, whereas in the CC, no exercise has been performed. Results: The findings revealed no significant (p > 0.05) interactions for CMJ and time to 30 m. Significant increases in 5 m split times were observed across all segments in the CC, as well as in the initial 5 m segment in the EC. Regarding sprint mechanics, a significant interaction was found in the effectiveness of horizontal force application (−2.42% in CC vs. −0.33% in EC). Step frequency demonstrated significant interaction in the 5–10 m segment (−1.79% in CC vs. 1.20% in EC) and decreased significantly in the 15–20 m segment in the CC (−2.03% in CC vs. −1.85% in EC). Conclusions: In conclusion, performance parameters reduced under the CC, whereas the BHDJ intervention stabilized these parameters or exhibited smaller performance variations than in the CC.

Biomechanics doi: 10.3390/biomechanics6010009

Authors: Thomas W. Kernozek C. Nathan Vannatta Kaelyn C. Wagner Kellie Hierl Sidney Smith Drew Rutherford

Background/Objectives: Running is associated with increased Achilles Tendon (AT) loading and cross-sectional area (CSA). Achilles tendinopathy is a common unilateral injury. Differences in AT loading variables between dominant and non-dominant lower extremities while running have not been characterized. This study examined the AT loading variables between dominant and non-dominant lower extremities in healthy recreational runners. Methods: Twenty-four females ran at 3.3 m/s (11.88 km/hr) on an instrumented treadmill. Achilles Tendon CSA (AT-CSA) was measured from ultrasound images. Kinematic and kinetic data were used as input into a musculoskeletal model. Paired t-tests examined inter-limb differences in peak vertical ground reaction force, Achilles Tendon-related loading variables (AT force, AT-CSA, AT stress), total gastrocnemius force, soleus force, foot strike angle, and stance time. Results: No differences were shown between dominant and non-dominant lower extremities in stance time, vertical ground reaction force, gastrocnemius and soleus force, AT force, AT-CSA, or AT stress. Foot strike angle was different between limbs (p = 0.015); however, the absolute difference was about 2°. Conclusions: These data indicated that AT loading was similar between dominant and non-dominant lower extremities in healthy female recreational runners. While some asymmetry can be expected during a bilateral task such as running, runners displayed differences in AT force and stress less than 18%. These data may assist clinicians in the assessment and management of runners recovering from AT tendinopathy.

Biomechanics doi: 10.3390/biomechanics6010008

Authors: Fernando Valencia Brizeida Gámez David Ojeda Hugo Salazar

Objective: The purpose of this study is to develop a mechatronic device capable of characterizing the kinematics of the knee joint, based on the acquisition and analysis of data focused on the knee joint point. Methods: A mechatronic device was designed using dimensional data from a participant’s lower limb (1.59 m, 57 kg), obtained through 3D scanning. The device, based on a proportional mechanism aligned with anatomical reference points, allows the evolution of the knee joint pivot point (PPKJ) to be recorded. Ten healthy subjects (aged 22–26 years, height 1.50–1.63 m, body mass 48–59 kg) were selected for testing. The device was placed on each knee to record joint trajectories during squats. The trajectories were classified into two groups: extension to flexion and flexion to extension. For each group, the average trajectory was calculated. Results: Forty PPKJ trajectories were obtained, divided into two sets: extension to flexion with a range of 8° to 51.3° and flexion to extension with a range of 6.7° to 56.83°, which allowed the mean trajectory and cubic polynomial regression to be calculated as the best approximation for characterizing the trajectory of the instantaneous center of rotation of the knee joint. Conclusions: The developed mechatronic device offers an accessible and non-invasive solution for recording the trajectory of the knee joint pivot point in individuals with characteristics like those in the study. This alternative approach could improve the representation of knee kinematics in the design of customized prostheses, exoskeletons, and rehabilitation devices for lower limbs.

Biomechanics doi: 10.3390/biomechanics6010007

Authors: Beyza Çiçek Neslihan Altuntaş Yılmaz Makbule Tuğba Tunçdemir Fatma Erdeo

Background: This study aimed to investigate the association between occlusal splint use and several key parameters, including body position perception, tongue pressure, temporomandibular joint dysfunction (TMD) severity, jaw functional limitation, and neck muscle endurance. Methods: A total of 157 individuals diagnosed with bruxism were screened, and 52 eligible participants were enrolled and divided into two groups: occlusal splint users (n = 26) and non-users (n = 26). Body position perception was assessed with a digital inclinometer, tongue pressure was measured using the Iowa Oral Performance Instrument (IOPI), and neck muscle endurance was evaluated by the Cranio-Cervical Flexion Test (CCFT). TMD severity and jaw functional limitation were assessed via the Fonseca Anamnestic Questionnaire and Jaw Functional Limitation Scale-20, respectively. Gender-based analyses showed higher TMD severity and mandibular limitation scores in females using occlusal splints than in males. Results: No statistically significant differences were found between the splint and non-splint groups in body position perception, tongue pressure and neck muscle endurance (p > 0.05). However, significant differences were observed in the Jaw Functional Limitation Scale (CFKS) subscales. Splint users reported higher functional limitations in chewing, mobility, and expression compared to non-splint users (all p = 0.000), with small effect sizes (d = 0.23–0.29). Conclusions: Occlusal splint use was not associated with better proprioception, orofacial muscle function, or TMD-related symptoms compared with non-splint users. However, splint users were associated with higher mandibular functional limitation based on CFKS subscale scores.

Biomechanics doi: 10.3390/biomechanics6010006

Authors: Kaden M. Kunz David G. Kirk John Wadner Nickolai J. P. Martonick

Background/Objectives: Limited ankle dorsiflexion has been associated with compensatory movement patterns throughout the lower extremity kinematic chain. This study investigated relationships between weight-bearing dorsiflexion capacity and lower limb kinematics and plantar pressure patterns during gait. Methods: Twenty-seven healthy adults (age: 22.8 ± 3.4 years) performed a weight-bearing lunge test (WBLT) and walked at a standardized pace across a pressure-sensing walkway while wearing inertial measurement units. Statistical Parametric Mapping assessed correlations between WBLT dorsiflexion and kinematic variables throughout the stance phase. Partial correlations controlled for walking velocity and were used to examine relationships with discrete plantar pressure measurements. Results: Reduced dorsiflexion capacity during the WBLT showed bilateral moderate associations with less ankle dorsiflexion (LEFT: peak r = 0.53; RIGHT: peak r = 0.60) and knee flexion (LEFT: peak r = 0.56; RIGHT: peak r = 0.58) during terminal stance and push-off. Proximal compensations demonstrated limb-specific patterns. Hip abduction was strongly negatively correlated in the left leg only (peak r = −0.65), while pelvic tilt showed bilateral relationships with opposing temporal patterns (LEFT: peak r = −0.58 early stance; RIGHT: peak r = 0.62 terminal stance). Plantar pressure analysis revealed that reduced dorsiflexion was associated with decreased heel relative impulse bilaterally (r = 0.53–0.56) and altered temporal patterns of midfoot loading on the left leg (r = 0.56). Conclusions: Limited dorsiflexion under load is associated with compensatory movement patterns extending from the ankle to the pelvis bilaterally. The evaluation of loaded ankle mobility should be considered an essential component of lower extremity movement assessment.

Biomechanics doi: 10.3390/biomechanics6010005

Authors: Josh Harris Kevin McCurdy Ting Liu Joni A. Mettler John Walker John W. Farrell

Background/Objectives: The effect of a high-volume, lower-body resistance exercise session on repeat power ability (RPA), defined as the ability to reach peak power (PP) or near PP during a high-volume resistance training session, remains unclear. The purpose of this study was to analyze the effects of recovery time and sex on loss of power within and across sets during a high-volume, low-load squat session. Methods: Twenty-five resistance-trained males and females (age = 25.5 ± 7.2 years; ht = 169.8 ± 8.9 cm; wt = 75.9 ± 16.9 kg) completed the study. Mean power output across five sets was measured during two sessions (one-minute rest vs. two-minute rest) using a linear position transducer in random order. Five sets at 45% of the participant’s 1RM were completed until power output decreased below 80% of the participant’s within-set PP for two consecutive repetitions or until volitional exhaustion occurred. The data were analyzed with a three-way ANOVA (recovery time by set by sex). Results: The males demonstrated a significant loss across sets for both the one-minute (194 watts) and two-minute recovery period (104 watts), while no change occurred for females in either condition. The males produced greater mean power across both recovery times and sets (p = 0.017). Further, a significant recovery time-by-set interaction was observed (p = 0.015). Mean power decreased an average of 111.3 watts during the one-minute recovery period compared to a loss of 54.0 watts during the two-minute recovery period. Lastly, within-set fatigue occurred during repetitions 9–11 and 11–14 during the one- and two-minute recovery periods, respectively. Conclusions: The data indicate that greater RPA occurs within and across sets with two minutes of rest. In addition, sex must also be considered when implementing a high-volume resistance training session with the goal of training repeat power ability.

Biomechanics doi: 10.3390/biomechanics6010004

Authors: Mark E. Pryer John Cronin Jonathon Neville Nick Mascioli Chris Slocum Sean Barger Aaron Uthoff

Background/Objectives: Despite athletes initiating sprints from dynamic starts during gameplay, sprint performance is traditionally measured from a static position. This article aimed to determine whether static start or “pickup” acceleration are related or relatively independent motor qualities by assessing their relationship and examining how athletes’ rank order changes between static and pickup conditions. Methods: Thirty-one male athletes (20.3 ± 5.3 years) completed two 30 m sprints from a static start and two 30 m pickup accelerations following 20 m paced entries at 1.5 and 3.0 m/s−1, regulated by an LED system. Peak acceleration (amax) was measured via a horizontal linear position encoder (LPE; 1080 Sprint). Results: The shared variance between amax from the static and pickup starts was R2 = 11.6–39.6%, indicating, for the most part, a great amount of unexplained variance. The shared variance between pickup acceleration entry velocities was R2 = 16.8%. A visual analysis of an individualized rank-order table confirmed that, for the most part, the fastest static-start athletes differed from the fastest pickup athletes. Conclusions: In summary, static and pickup acceleration appear to be distinct motor abilities, most likely requiring a paradigm shift in strength and conditioning practices for acceleration assessment and development.

Biomechanics doi: 10.3390/biomechanics6010003

Authors: Mary Claire Geneau David L. Carey Paul B. Gastin Sam J. Robertson Lachlan P. James

Background/Objectives: This study evaluated the differences in force–time characteristics of different incrementally loaded countermovement jumps (CMJs) and assessed their relationship to one-repetition maximum (1-RM) back squat performance. Methods: Nineteen resistance-trained males participated in this cross-sectional study, performing CMJs under six conditions (0%, 20%, 40%, 60%, 80%, and 100% body mass) followed by a 1-RM back squat. Multiple regression models were used to evaluate the relationship between discrete CMJ metrics (net concentric impulse, net concentric mean force, eccentric duration) with 1-RM values. Additionally, one-dimensional statistical parametric mapping (SPM) was used to evaluate the intact force–time curve between jump conditions. Results: The multiple regression models explained 53–66% of the variance in 1-RM squat performance, which was greatest under the 80% body mass condition. One-dimensional SPM analysis revealed significant differences in force–time curves across all loading conditions. Conclusions: These findings demonstrate that metrics from a loaded CMJ explained up to 66% of variance in the 1-RM back squat, suggesting the two tests are independent measures of strength. Further, each loaded jump condition elicited unique force-time curves, suggesting that each load requires a different neuromuscular technique.

Biomechanics doi: 10.3390/biomechanics6010002

Authors: Stefano Vando Leonardo Alexandre Peyré-Tartaruga Ionel Melenco Wissem Dhahbi Luca Russo Johnny Padulo

Objectives: This study aimed to assess stroke coordination and biomechanics in elite U23 male kayakers under valid on-water conditions (instrumented K1 kayak on a competition lake) across race-relevant stroke frequencies (60, 80, and 100 strokes·min−1). Methods: To achieve our aims, twelve male athletes (age 21.00 ± 0.47 years) completed 500 m trials at three randomized paddle frequencies (60, 80, 100 strokes·min−1) with 10 min of passive recovery in-between. Data were collected with inertial measurement units, and a customized seat/footrest with integrated strain-gauge sensors. Results: Principal Component Analysis identified four key components: Mechanical Work, Mechanical Energy, Stroke Variability (PCI, Phase Coordination Index), and boat acceleration, accounting for 76% of total variance. Linear mixed-effects models (within-subject LME; Participant random intercept; Satterthwaite df) revealed that Mechanical Work (χ2 = 17.10, p < 0.001) and Mechanical Energy (χ2 = 53.10, p < 0.001) increased significantly with stroke frequency. Phase Coordination Index showed a significant increase at 60 and 100 strokes·min−1 (χ2 = 16.78, p < 0.001; t = 4.78, p < 0.001), while boat acceleration was not significantly affected (χ2 = 4.95, p = 0.08). The PCI correlated negatively with Mechanical Work (r = −0.37, p = 0.022) and positively with boat acceleration (r = 0.39, p = 0.010). Effect sizes were moderate to large (ηp2 = 0.18–0.36; corresponding 95% confidence intervals are reported in the main text). For the primary mechanical indicator (Paddle Factor), the mixed-effects model yielded a marginal R2 = 0.57, reflecting the proportion of variance explained by cadence. Conclusions: Approximately 80 strokes·min−1 may represent a condition in which coordination metrics appear comparatively favorable. These findings are exploratory and hypothesis-generating, not prescriptive. No causal inference can be drawn, and any training application attempts should await replication in larger, longitudinal and randomized studies.

Biomechanics doi: 10.3390/biomechanics6010001

Authors: Dayanne R. Pereira Danilo S. Catelli Paulo R. P. Santiago Bruno L. S. Bedo

Background/Objectives: Marker-based motion capture remains widely used for lower limb kinematics due to its high precision, although its application is often constrained by elevated operational costs and the requirement for controlled laboratory environments. Markerless methods, such as MediaPipe offer a promising alternative for extending biomechanical analyses beyond traditional laboratory settings, but evidence supporting their validity in controlled tasks is still limited. This study aimed to validate a pixel-based markerless pipeline for two-dimensional kinematic analysis of hip and knee motion during squatting. Methods: Ten healthy volunteers performed three squats with a maximum depth of 90°. Kinematic data were collected simultaneously using marker-based and markerless systems. For the marker-based method, hip and knee joint angles were calculated from marker trajectories within a fixed coordinate system. For the markerless approach, a custom pixel-based pipeline was developed in MediaPipe 0.10.26 to compute bidimensional joint angles from screen coordinates. A paired t-test was conducted using Statistical Parametric Mapping, and maximum flexion values were compared between systems with Bland–Altman analysis. Total range of motion was also analyzed. Results: The markerless pipeline provided valid estimates of hip and knee motion, despite a systematic tendency to overestimate joint angles compared to the marker-based system, with a mean bias of −17.49° for the right hip (95% LoA: −51.89° to 16.91°). Conclusions: These findings support the use of markerless tools in clinical contexts where cost and accessibility are priorities, provided that systematic biases are taken into account during interpretation. Overall, despite the systematic differences, the 2D MediaPipe-based markerless system demonstrated sufficient consistency to assist clinical decision-making in settings where traditional motion capture is not available.

Biomechanics doi: 10.3390/biomechanics5040106

Authors: Estélio Henrique Martin Dantas Ronald Bispo Barreto Miguel Angel Narvaez Silva Marcos Antonio Almeida-Santos Guido Belli Luca Russo

Background: Street running has seen rapid growth due to its health benefits and accessibility, leading to a simultaneous rise in running-related injuries, particularly among recreational and professional street runners. Medial Tibial Stress Syndrome (MTSS) is a common injury affecting up to 15% of athletes and posing significant risks to runners of all levels of participation. Objective: This study aimed to investigate the strength and kinematic differences in the lower limbs of runners diagnosed with MTSS compared to asymptomatic runners. Methods: A total of 56 participants were divided into an MTSS group (27 runners) and a healthy control group (29 runners). Participants were evaluated for demographics, physical activity level, pain threshold using algometry, and running kinematics obtained through high-resolution 2D video analysis with Kinovea software. Lower-limb muscle strength was measured using an isometric Lafayette® digital dynamometer. Results: Although there were no significant differences in age or anthropometric measures, MTSS runners exhibited lower initial (∆% = 10.6%, p = 0.002) and intermediate (∆% = 8.7%, p = 0.026) running speeds. Pain assessment revealed significant lower pain thresholds in the MTSS group. Kinematic analysis identified greater foot-strike angles (left foot: ∆% = 31.9%, p = 0.004; right foot: ∆% = 25.9%, p = 0.0049) at initial speeds in MTSS runners, while other parameters like medial calcaneus rotation, push-off angles, and support time did not differ significantly. Additionally, MTSS runners demonstrated reduced strength in the quadriceps femoris (QF—Left QF: ∆% = −28.5%, p = 0.0049; Right QF: ∆% = −28.2%, p = 0.003). Conclusions: MTSS appears to affect female and male runners. MTSS may be attributed to a weaker quadriceps strength, higher heel contact angles during foot strike, or both, suggesting that interventions focusing on the improvement of these factors may be beneficial in preventing and treating MTSS.

Biomechanics doi: 10.3390/biomechanics5040105

Authors: Christopher James Keating Anja Turner Sarah Jane Viljoen Matteo Vitarelli

Background: Quantitative gait analysis is essential in both clinical and research contexts; however, traditional marker-based motion capture systems are costly and burdensome. Advances in three-dimensional markerless motion capture (3D-MMC) offer more accessible alternatives; however, they lack standardized protocols. Objectives: The present study aimed to establish a standardized protocol and procedures for 3D MMC-based gait analysis using OpenCap and to quantify the reliability and within-session precision of key spatiotemporal gait parameters. Methods: Fifty healthy university students (mean age = 22.15 ± 2.12 years) completed walking trials along a 10 m walkway under single-task (ST) and five dual-task (DT) conditions of varying cognitive complexity. Gait data were collected using a two-camera OpenCap 3D-MMC system, with standardized calibration, lighting, clothing, and trial segmentation. Spatiotemporal parameters were extracted, and within-session relative reliability was quantified using two-way mixed-effects intraclass correlation coefficients, and absolute reliability was quantified using general linear model–derived within-subject error (standard error of measurement, SEM) and minimal detectable change (MDC). Repeated-measures ANOVA with Bonferroni corrections were used to examine condition-related differences. Results: Of 500 trials, 491 (98.2%) were successfully processed. Within-subject test–retest reliability ranged from moderate to excellent for all variables, with gait speed, stride length, and cadence showing the highest ICCs and smallest SEM and MDC values, and step width and double support exhibiting larger measurement error. Conclusions: This study establishes a standardized 3D-MMC protocol for gait analysis using OpenCap and demonstrates good to excellent within-session relative and absolute reliability for most spatiotemporal gait parameters in healthy young adults. Dual-task walking is used here to illustrate how trial-averaged OpenCap measurements and their SEM/MDC can be used to determine which condition-related changes in gait exceed measurement error.

Biomechanics doi: 10.3390/biomechanics5040104

Authors: Doris Posch Markus Antretter Martin Burtscher Sebastian Färber Martin Faulhaber Lorenz Immler

Background: Foam rolling has become an increasingly popular self-myofascial release (SMR) technique among athletes to prevent injuries, improve recovery, and increase athletic performance. This study investigated how SMR improves mechanical and movement efficiency in recreational road cyclists. Methods: We conducted an exploratory randomized controlled trial (RCT) to investigate the effects of SMR using a foam roller on biomechanical and physiological performance parameters over a six-month period. A total of 32 male participants, aged 26–57 years, with a mean Body Mass Index (BMI) of 24.0 kg/m2 (SD = 2.2), were randomly assigned to either an intervention group (n = 16), which incorporated a standardized SMR program into their post-exercise recovery, or a control group (n = 16), which followed the same cycling protocol without SMR. The training program included heart rate-controlled strength endurance intervals. As the primary target, the variables we investigated included torque effectiveness, leg force symmetry, and pedal smoothness. Secondary measurements included submaximal oxygen uptake (VO2) as well as bioelectrical variables, which we analyzed using classic, repeated-measures ANOVA models and descriptive statistical methods. Results: The analysis revealed significant interaction effects in favor of the intervention group for torque effectiveness (η2p = 0.434), leg strength symmetry (η2p = 0.303), and pedal smoothness (η2p = 0.993). No significant group × time interactions were found for submaximal VO2 or bioelectrical parameters. Conclusions: Our findings indicate that foam rolling may serve as an effective adjunct to endurance training by enhancing functional neuromuscular performance in cyclists, particularly in torque control and pedal coordination. Its impact on aerobic efficiency and muscle composition appears to be minimal. The results support theoretical models that attribute SMR benefits to proprioceptive, circulatory, and neuromuscular mechanisms rather than structural tissue adaptations.

Biomechanics doi: 10.3390/biomechanics5040103

Authors: Fagner Luiz Pacheco Salles Augusto Gil Pascoal

Background: Shoulder exercises using elastic resistance integrated within the kinetic chain appear to modify scapular control strategies; however, a deeper understanding of these mechanisms is still needed. Objectives: We aim to compare three-dimensional scapular kinematics during two exercises performed on different bases of support, under both non-resisted and resisted conditions in asymptomatic adults. Methods: This cross-sectional study analyzed three-dimensional shoulder kinematics in 36 healthy adult male participants during the overhead squat and kneeling position exercises. Movement patterns were evaluated by phase using statistical parametric mapping. Results: Scapular internal/external rotation demonstrated a main effect for exercise type (p = 0.04), a main effect for resistance conditions (p < 0.00), and a significant exercise–resistance interaction (p = 0.04) during arm elevation. During the lowering phase, a main effect was observed for exercise types (p = 0.04) and exercise conditions (p < 0.00). Scapular upward rotation showed a main effect for exercise type (p = 0.02) and resistance conditions (p = 0.04) during arm elevation. During the lowering phase, a significant main effect was observed for exercise type (p = 0.01) and exercise conditions (p < 0.00). Scapular posterior tilt presented a main effect for exercise type (p < 0.00), a main effect for exercise condition (p = 0.01), and an exercise–resistance interaction (p = 0.04) during arm elevation. During the lowering phase, a main effect for exercise type (p < 0.00), a main effect for exercise condition (p = 0.02), and an exercise–resistance interaction (p = 0.00). Conclusions: The resistance and exercises demonstrated different kinematic strategies that helped maintain scapular stability during movement.

Biomechanics doi: 10.3390/biomechanics5040102

Authors: Noppharath Sangkarit Weerasak Tapanya

Background: Double-support percentage (DS%) is often interpreted as a proxy for dynamic gait stability, yet its biomechanical meaning is confounded by its strong inverse coupling with walking speed. This distinction is critical in Parkinson’s disease (PD), where bradykinetic gait inherently prolongs DS%. To isolate speed-independent stability demands, we introduced a model-based Stability Reserve Index (SRI), representing the deviation between predicted and observed double support after normalizing for velocity and anthropometrics. Methods: Using an open-access dataset of 63 individuals with PD (ON medication; Hoehn & Yahr 1–3) and 63 matched controls, step-based DS% was modeled using ANCOVA, incorporating centered walking speed, group, their interaction, and covariates. Predicted DS% at the sample’s grand mean speed was subtracted from observed DS% to derive the SRI, indexing whether double support exceeded expectations for a given biomechanical operating point. Results: PD participants walked slower than controls (p < 0.001), but once velocity was accounted for, DS% no longer differed between groups (p = 0.795–0.880), and the DS%–speed coupling remained intact (interaction p = 0.387). Speed-normalized predicted DS% (p = 0.159) and the SRI (p = 0.989) were likewise similar across groups. Within PD, SRI did not correspond to UPDRS-III or Hoehn & Yahr stage (ρ = 0.129–0.223, p > 0.05). Conclusions: These findings indicate that double-support behavior in mild-to-moderate PD is largely velocity-driven rather than reflecting altered dynamic stabilization strategies. While conceptually grounded in stability reserve theory, the SRI showed limited discriminatory value under ON-medication walking, suggesting that more sensitive multidimensional metrics—integrating CoM dynamics, variability, and step-to-step control—may be required to capture early instability in PD.

Biomechanics doi: 10.3390/biomechanics5040101

Authors: Christian Mitschke Tobias Heß Thomas L. Milani Pierre Kiesewetter

Background/Objectives: Running is one of the most popular physical activities worldwide and have been widely studied in relation to performance and injury prevention. In addition to measurements conducted under standardized laboratory conditions, inertial measurement units (IMUs) allow for the assessment of biomechanical parameters in real-world settings—particularly during endurance runs. The aim of this study was to investigate how running a half-marathon under field conditions affects exertion and various biomechanical parameters, as measured using IMUs. Methods: Twenty runners completed a half-marathon on a flat, even-surfaced walkway at a self-selected, constant pace corresponding to a brisk training run. In addition to lower limb biomechanics, heart rate (HR) and ratings of perceived exertion (REP) were also recorded. Results: A significant increase in both HR and RPE was observed toward the end of the half-marathon, indicating the presence of fatigue during the later stages of the run. The biomechanical results further demonstrate that this fatigue was associated with increased peak tibial acceleration, peak angular velocity in the sagittal plane of the foot, and peak rearfoot eversion velocity, while foot strike angle, stride frequency, and stride length remained unchanged. Furthermore, a progressive increase in ground contact time and a decrease in flight time were observed over the course of the run, resulting in an increased duty factor. Conclusions: These findings highlight the value of IMU-based assessments for detecting fatigue-related biomechanical changes during prolonged runs in real-world conditions, which may contribute to early identification of overload and inform injury prevention strategies.

Biomechanics doi: 10.3390/biomechanics5040100

Authors: Carina Thomas Kevin Nolte Marcus Schmidt Thomas Jaitner

Background: Marker-based motion capture systems are commonly used for three-dimensional movement analysis in sports. Novel, markerless motion capture systems enable the collection of comparable data under more time-efficient conditions with higher flexibility and fewer restrictions for the athletes during movement execution. Studies show comparable results between markerless and marker-based systems for kinematics of the lower extremities, especially for walking gait. For more complex movements, such as throwing, limited data on the agreement of markerless and marker-based systems is available. The aim of this study is to compare the outcome of a video-based markerless motion capture system with a marker-based approach during an artificial basketball-throwing task. Methods: Thirteen subjects performed five simulated basketball throws under laboratory conditions, and were recorded simultaneously with the marker-based measurement system, as well as two versions of a markerless measurement system (differing in their release date). Knee, hip, shoulder, elbow and wrist joint angles were acquired and root mean square distance (RMSD) was calculated for all subjects, parameters and attempts. Results: The RMSD of all joint angles of the marker-based and markerless systems ranged from 7.17° ± 3.88° to 26.66° ± 14.77° depended on the joint. The newest version of the markerless system showed lower RMSD values compared to the older version, with an RMSD of 16.68 ± 5.03° for elbow flexion, capturing 93.84% of the data’s RMSD of 22.22 ± 5.52, accounting for 87.69% of the data. While both versions showed similar results for right knee flexion, lower differences were observed in the new version for right hip flexion, with an RMSD of 8.17 ± 3.75 compared to the older version’s 13.24 ± 5.78. Additionally, the new version demonstrated lower RMSD values for right hand flexion. Conclusions: Overall, the new version of the markerless system showed lower RMSD values across various joint angles during throwing movement analysis compared to the older version. However, the differences between markerless and marker-based systems are especially large for the upper extremities. In conclusion, it is not clearly explainable if the detected inter-system differences are due to inaccuracies of one system or the other, or a combination of both, as both methodologies possess special limitations (soft tissue vibration or joint center position accuracy). Further investigations are needed to clarify the accordance between markerless and marker-based motion capture systems during complex movements.

Biomechanics doi: 10.3390/biomechanics5040099

Authors: Mishal Raza-Taimuri Ian Y. Chen Hamid Sadat

Background/Objectives: Calcific aortic valve disease (CAVD) is a progressive condition marked by thickening and calcification of the valve leaflets, leading to impaired cardiac function and increased cardiovascular risk. As disease progression is strongly influenced by hemodynamics and lipid accumulation, computational modeling provides a powerful tool for understanding the biomechanical drivers of calcification. Methods: This study investigates the effects of coronary artery flow and varying left ventricular outflow tract (LVOT) velocity profiles on low density lipoprotein (LDL) accumulation and associated aortic valve calcification using a partitioned fluid–structure interaction framework coupled with scalar transport modeling, with a focus on understanding the differential behaviors of the three valve leaflets: the non-coronary cusp (NCC), right coronary cusp (RCC), and left coronary cusp (LCC). Four distinct LVOT flow velocity profiles (anterior, lateral, posterior, and medial) and coronary flow are simulated to determine their effects on the distribution of LDL accumulation and associated calcification across the valve leaflets. Results/Conclusions: Our results indicate that the RCC experiences greatest excursion and lowest calcification. The LCC shows lowest excursion and slightly higher susceptibility for calcification. Finally, the NCC experiences intermediate excursion, but is most prone to calcification.

Biomechanics doi: 10.3390/biomechanics5040098

Authors: Ryosuke Karashima Shintaro Kishimoto Takuya Ibara Kiyotaka Hada Tatsuo Motoyama Masayuki Kawashima Yusuke Murofushi Hiroshi Katoh

Background: The relationship between varus thrust (VT) during gait and static limb alignment on radiography in knee osteoarthritis (OA) remains unclear. Therefore, the present study investigated the association between the tibial inclination angle (TA), which was noninvasively measured from the body surface, and radiographic parameters. In Addition, this study analyzed how TA changes under different loading conditions (ΔTA) relate to VT acceleration (VTA) during early stance using an inertial measurement unit (IMU) sensor. Methods: Nineteen female patients (mean age: 63.5 ± 8.6 years) with knee OA or medial meniscus injury were included. The TA was defined as the angle between the tibial mechanical axis and a vertical line from the floor, which was measured in standardized standing and supine positions. The ΔTA was calculated as the difference between these positions. To assess lower limb alignment, the femorotibial angle (FTA) and joint line convergence angle (JLCA) were measured. The VTA was measured using IMU sensors on the thigh and tibia, and the differences between lateral and medial VTA were defined as femoral and tibial ΔVTA, respectively. Spearman’s correlation coefficient and linear regression were used for analysis. Results: The standing TA was significantly correlated with the FTA (ρ = 0.47, p = 0.04) and JLCA (ρ = 0.80, p < 0.01). The ΔTA was significantly associated with femoral ΔVTA (β = 0.70, p < 0.01) and tibial ΔVTA (β = 0.67, p < 0.01). Conclusions: Surface-measured TA reflects radiographic alignment. The ΔTA also captures dynamic instability not explained by static measures, suggesting its potential utility as an assessment indicator, although further validation is warranted.

Biomechanics doi: 10.3390/biomechanics5040097

Authors: Georgios Giarmatzis Nikolaos Aggelousis Erasmia Giannakou Ioanna Karagiannakidou Evangelia Makri Anna Tsiakiri Foteini Christidi Paraskevi Malliou Konstantinos Vadikolias

Background/Objectives: While strength training interventions improve walking performance in stroke survivors, the underlying neuromuscular mechanisms remain poorly understood. This study investigated muscle-level adaptations following a 12-week moderate-to-high-intensity strength training program in ten chronic stroke survivors using comprehensive musculoskeletal modeling analysis. Methods: Three-dimensional gait analysis was performed pre- and post-intervention, with subject-specific OpenSim models estimating individual muscle forces, powers, and work capacities throughout stance phase. Results: Non-paretic hip flexor negative work capacity increased significantly (0.033 to 0.042 J/kg, p = 0.033, Cohen’s d = 0.47), driven by enhanced rectus femoris power absorption during late stance that mechanistically facilitated trunk acceleration through leg deceleration. Knee extensor force generation showed increasing trends during loading response in both limbs. During push-off, ankle plantar flexor force generation showed trends toward bilateral improvements, primarily through paretic soleus and gastrocnemius contributions, though power output remained unchanged, indicating persistent velocity-dependent muscular deficits. Conclusions: Improved gait performance in both limbs demonstrates that strength training produces functionally beneficial bilateral muscle-level reorganization. The absence of a control group limits causal inference, though the observed biomechanical adaptations align with functional improvements, supporting the integration of strength training into comprehensive stroke rehabilitation protocols targeting locomotor recovery.

Biomechanics doi: 10.3390/biomechanics5040096

Authors: Paulina Sofía Valle-Oñate José Luis Jínez-Tapia Luis Gonzalo Santillán-Valdiviezo Carlos Ramiro Peñafiel-Ojeda Deysi Vilma Inca Balseca Juan Carlos Tixi Pintag

Background: Children with spastic hand impairments resulting from cerebral palsy or neuromuscular disorders often exhibit a restricted range of motion and diminished functional use. Rehabilitation devices that assist joint mobilization can enhance therapeutic outcomes, yet few solutions target pediatric populations. Methods: This study aimed to design, implement, and preliminarily evaluate a biomechanical device tailored to promote flexo-extension, radial–ulnar deviation, and supination movements in spastic hands of school-aged children. A prototype combining a motor-driven actuation system, adjustable wrist and finger supports, and a MATLAB-based graphical user interface was developed. Two participants (aged 8 and 10) with clinically diagnosed spastic hemiparesis underwent 25-minute sessions over 15 consecutive days. Joint angles were recorded before and after each session using an electro-goniometer. Data normality was assessed via the Shapiro–Wilk test, and pre–post differences were analyzed with the Wilcoxon signed-rank test (α = 0.05). Results: Both participants demonstrated consistent increases in their active range of motion across all measured planes. Median flexo-extension improved by 12.5° (p = 0.001), ulnar–radial deviation by 7.3° (p = 0.002), and supination by 9.1° (p = 0.001). No adverse events occurred, and device tolerance remained high throughout the intervention. Conclusions: The device facilitated statistically significant enhancements in joint mobility in a small pediatric cohort, supporting its feasibility and safety in spastic hand rehabilitation. These preliminary findings warrant larger controlled trials to confirm the device’s efficacy, optimize treatment protocols, and assess its long-term functional benefits.

Biomechanics doi: 10.3390/biomechanics5040095

Authors: Hannah Schmidt Vernon Coffey Anna Lorimer

Background/Objectives: Jumping is a common movement pattern, often used in testing for both performance monitoring and decision-making in return to sport. Current methods of assessing movement coordination are time-, technology- and expertise-dependent. The use of force–time curves to analyse the execution of the movement would provide an accessible and detailed analysis of movement. Methods: Thirty endurance runners and triathletes (18–40 years) completed five maximal countermovement jumps (CMJs) and five maximal standing broad jumps (SBJs). Participants were grouped (HIGH, MOD and LOW) according to the magnitude of the time interval between peak hip and peak knee extension velocity. A separate grouping according to the magnitude of the time interval between peak knee and peak ankle extension velocity was created. A one-way Statistical non-Parametric Mapping ANOVA, with alpha set at 0.05 and iterations at 10,000, was used to compare vertical ground reaction force (CMJ and SBJ), horizontal ground reaction force (SBJ) and resultant ground reaction force (SBJ) between the three hip–knee groups and a separate analysis for the three knee–ankle groups. Results: Significant differences were observed between time interval groups in both hip–knee coordination and knee–ankle coordination for both jump types (p < 0.001) at several regions of the force–time curves. Conclusions: The results suggest there is potential for statistical parametric mapping analysis to detect differences in movement coordination patterns from force curves. Further research is needed to help explain the differences observed in the curves for the kinematic groupings, to explore different combinations of hip–knee and knee–ankle kinematic patterns and to associate curve characteristics with performance indicators.

Biomechanics doi: 10.3390/biomechanics5040094

Authors: Xishi Zhu Devin K. Kelly Grayson Kim Joe M. Hart Jiaqi Gong

Background/Objectives: Outcomes following Anterior Cruciate Ligament (ACL) reconstruction vary widely among patients, yet existing classification techniques often lack transparency and clinical interpretability. To address this gap, we developed a multi-modal framework that integrates gait dynamics with patient-specific characteristics to enhance personalized assessment of ACL reconstruction outcomes. Methods: Participants, both post-ACL reconstruction and healthy controls, were equipped with inertial measurement unit (IMU) sensors on bilateral wrists, ankles, and the sacrum during standardized locomotion tasks. Using the Phase Slope Index (PSI), we quantified causal relationships between sensor pairs, hypothesizing that (1) PSI-derived metrics capture discriminative biomechanical interactions; (2) task-specific differences in segment coordination patterns influence model performance; and (3) recovery duration modulates classifier confidence and the structure of high-dimensional data distributions. Classification models were trained using PSI features, and permutation-based sensor importance analyses were conducted to interpret task-specific biomechanical contributions. Results: PSI-based classifiers achieved 96.37% accuracy in distinguishing ACL reconstruction outcomes, validating the first hypothesis. Permutation importance revealed that jogging tasks produced more focused importance distributions across fewer sensor pairs while improving accuracy, confirming task-specific coordination effects (hypothesis two). Visualization via t-SNE demonstrated that longer recovery durations corresponded to reduced model confidence but more coherent feature clusters, supporting the third hypothesis. Conclusions: By integrating causal gait metrics and patient recovery profiles, this approach enables interpretable and high-performing ACL outcome prediction. Quantitative evaluation measures—including model confidence and t-SNE cluster coherence—offer clinicians objective tools for personalized rehabilitation monitoring and data-driven return-to-sport decisions.

Biomechanics doi: 10.3390/biomechanics5040093

Authors: Gregory M. Lupica Connor J. Schamblin Victor T. Hung Hunter R. Hitchens Michelle H. McGarry Gregory J. Adamson Thay Q. Lee

Background: The radiocapitellar articulation of the elbow joint is particularly susceptible to subluxation and dislocation. Joint stability can be quantified using the stability ratio, a biomechanical parameter of joint stability defined as the ratio of the maximum dislocating force the joint can resist in relation to the joint compressive force. The purpose of this study was to biomechanically assess the stability of the radiocapitellar joint in the anterior and posterior direction across varying degrees of elbow flexion. Methods: Eight fresh-frozen cadaveric elbows, average age 68.9 years (range 61–73 years; 3 males and 5 females; 7 left and 1 right) were tested. The distal humerus and proximal radius were dissected of all soft tissues to isolate the radiocapitellar articulation. The radius and humerus were mounted on a custom jig that allows for positional adjustment and incorporates a material testing machine. Each specimen was mounted at neutral forearm position and tested at 30, 45, and 60 degrees of anatomical elbow flexion. All specimens were subjected to 10 mm of anterior–posterior displacement for 5 cycles at 20 mm per minute with 40 N of compressive load. Subluxation force, displacement at subluxation force, linear stiffness, stability ratio, and energy absorbed were calculated. Results: In all degrees of elbow flexion, the stability ratio in the posterior direction was significantly higher than the anterior direction by an average of 39.8 ± 32.6% (p < 0.025). Maximum subluxation force was also significantly higher in the posterior direction when compared to the anterior direction (p < 0.027). There was no significant difference in any other parameters. Conclusions: The stability ratio and maximum subluxation force of the radiocapitellar joint when positioned in neutral forearm rotation are significantly greater in the posterior direction when compared to the anterior direction. This finding provides quantitative insights and a biomechanical rationale for the propensity of anterior instability in the radiocapitellar joint.

Biomechanics doi: 10.3390/biomechanics5040092

Authors: Seongok Chae Hyun Soo Kang Hojik Lee Yoo-Jin Jun SeungMyung Choi Young-Phil Yune Hyung-Soon Park

Plantar fasciitis (PFS) is a leading cause of heel pain, yet its clinical course varies widely. Although plantar fascia thickness (PFT) is often used as a pain marker, its prognostic value remains unclear. Objective: This study investigates whether foot arch morphology underlies distinct biomechanical profiles in PFS patients, potentially explaining the variability in its presentation. Methods: The cross-sectional study included 30 patients with PFS and 10 healthy controls. PFS patients were classified by arch type (pes rectus, pes planus, pes cavus) using the Arch Height Index (AHI). Baseline comparisons between healthy controls and PFS subgroups assessed PFT, Foot Function Index (FFI), joint stiffness ratio, and gait parameters. Results: PFT differed across groups but was not significantly associated with FFI scores (p = 0.233). The pes cavus group exhibited a lower metatarsophalangeal (MTP) stiffness ratio compared with healthy (p < 0.05). Pes planus and pes rectus groups showed excessive pronation, and the pes cavus group showed limited ankle dorsiflexion, indicating distinct gait mechanisms (p < 0.05). Conclusions: Foot arch morphology influences gait biomechanics, stiffness, and PFT in individuals with PFS. Incorporating individual arch types into clinical decision-making may facilitate more personalized interventions and improve treatment outcomes.

Biomechanics doi: 10.3390/biomechanics5040091

Authors: Robin Heilmann Stefan Schleifenbaum Peter Melcher Christoph-Eckhard Heyde Nicolas Heinz von der Höh

Background: In spinal fusion surgery, intersomatic compression force is currently applied subjectively by the operating surgeon, despite its critical role on implant stability and risk of subsidence. No standardized measurement or guideline exists to control or quantify the amount of force applied. Methods: In a two-phase exploratory study, we evaluated whether proprioceptive muscle memory allows reliable reproduction of applied manual compression forces. In Phase 1, 30 participants applied force to a compression clamp equipped with a strain gauge, simulating spinal interbody compression on a 3D-printed vertebral model. They were then asked to reproduce this force using a hand dynamometer at defined time intervals. In Phase 2, intraoperative compression forces applied during spinal fusion procedures were retrospectively assessed by having the operating surgeon reproduce the force on a dynamometer. Results: Participants were able to reproduce their initial manual compression force within a 15% deviation, even 15 min after the initial application. In 116 clinical cases, an average compression force of 146.3 ± 18.5 N was recorded. No significant differences were observed across different spinal segments. Conclusions: These findings provide initial data toward defining a reproducible reference range for indirect intraoperative compression assessment. Standardization of applied force may help improve biomechanical outcomes and reduce complications such as implant migration, pseudarthrosis, or cage subsidence.

Biomechanics doi: 10.3390/biomechanics5040090

Authors: Federico Caramia Emanuele D’Angelantonio Leandro Lucangeli Valentina Camomilla

Background: Respiratory exercises play a key role in rehabilitation programs, especially for older adults and individuals with chronic pulmonary conditions. Despite growing interest in wearable sensors for home-based care, structured reference metrics to quantitatively characterize respiratory exercises are still limited. This study aimed to provide a quantitative characterization of respiratory exercises and evaluate the level of agreement between a low-cost prototypical sensor and a commercial one. Methods: Eleven older adults (9 females; age = 72.6 ± 5.0 years; height = 1.66 ± 0.09 m; mass = 68 ± 10 kg) performed a structured respiratory exercises protocol. Algorithms were developed to identify respiratory cycles, their execution time, and parameters related to respiratory capacity, using accelerometer signals from the two wearable sensors placed on the rib cage. Results: The average respiratory cycle duration ranged from 2.8 to 4.3 s, with normalized inspiratory and expiratory peaks. Tidal volume variability was minimal, confirming consistency in breathing patterns across exercises. User comfort was high (mean VAS = 8.7). Sensor comparison confirmed strong agreement between the two sensors in detecting respiratory cycles, though some variability was observed in timing and tidal volume estimation. Conclusions: These findings suggest that even simple accelerometers can reliably capture key respiratory parameters, supporting the feasibility of using wearable sensors to monitor structured respiratory exercises performed in home-based settings.

Biomechanics doi: 10.3390/biomechanics5040089

Authors: Yuto Tanaka Yoshiaki Ono Yosuke Tomita

Background/Objective: Postural stability and motor coordination require precise regulation of agonist and antagonist muscle activities. Jaw clenching modulates neuromuscular control during static and reactive postural tasks. However, its effects on dynamic voluntary movement remain unclear. This pilot study aimed to investigate the effects of jaw clenching on muscle activity and kinematics during repetitive single-leg sit-to-stand task performance. Methods: Eleven healthy adults (age: 21.2 ± 0.4 years; 6 males and 5 females; height: 167.9 ± 9.6 cm; body weight: 59.7 ± 8.1 kg) performed repetitive single-leg sit-to-stand tasks for 30 s under jaw-clenching and control conditions. Electromyography (EMG) signals from eight muscles and kinematic data from 16 inertial measurement unit sensors were analyzed, focusing on the seat-off phase. Results: Jaw clenching resulted in a significantly lower success rate than the control condition (success rate: 0.96 ± 0.13 vs. 0.78 ± 0.29, p = 0.047). Under the jaw clenching condition, failed trials exhibited higher medial gastrocnemius and masseter EMG activity (p < 0.001), lower erector spinae longus EMG activity (p < 0.001), and altered kinematics, including increased trunk yaw and roll angles (p < 0.001). Jaw clenching increased the coactivation of the gastrocnemius and tibialis anterior muscles (p < 0.001), disrupting the reciprocal muscle patterns critical for task performance. Conclusions: These findings suggest that jaw clenching may reduce task performance by altering neuromuscular coordination during dynamic postural tasks.

Biomechanics doi: 10.3390/biomechanics5040088

Authors: Serena Cerfoglio Jorge Lopes Storniolo Edilson Fernando de Borba Paolo Cavallari Manuela Galli Paolo Capodaglio Veronica Cimolin

Background: Gait analysis plays a key role in detecting and monitoring neurological, musculoskeletal, and orthopedic impairments. While marker-based motion capture (MoCap) systems are the gold standard, their cost and complexity limit routine use. Recent advances in computer vision have enabled markerless smartphone-based approaches. OpenCap, an open-source platform for 3D motion analysis, offers a potentially accessible alternative. This review summarizes current evidence on its accuracy, limitations, and clinical applicability in gait assessment. Methods: A search was performed in major scientific databases to identify studies published from OpenCap’s release in 2023 to June 2025. Articles were included if they applied OpenCap to human gait and reported quantitative biomechanical outcomes. Both validation and applied studies were considered, and findings were synthesized qualitatively. Results: Nine studies were included. Validation research showed OpenCap achieved generally acceptable accuracy kinematics (RMSE 4–6°) in healthy gait, while increased errors were reported for pathological gait patterns. Applied studies confirmed feasibility in different clinical conditions, though trial-to-trial variability remained higher than MoCap, and test–retest reliability was moderate, with minimal detectable changes often exceeding 5°, limiting sensitivity to subtle clinical differences. Conclusions: OpenCap is a promising, low-cost tool for gait screening, remote monitoring, and tele-rehabilitation. Its strengths lie in accessibility and feasibility outside laboratory settings, but limitations in multiplanar accuracy, pathological gait assessment, and kinetic estimation currently preclude its replacement of MoCap in advanced clinical applications. Further research should refine algorithms and standardize protocols to improve robustness and clinical utility.

Biomechanics doi: 10.3390/biomechanics5040087

Authors: Yota Abe Aimi Tayama Tomoki Iizuka Yosuke Tomita

Background/Objectives: This study aimed to provide preliminary normative data on intersegmental coordination patterns during heel rises at different knee joint positions and across various phases and periods. Methods: Twelve 21-year-old university students from the same cohort performed heel rises in knee-extended and knee-flexed conditions. Shank and foot kinematics were recorded using the VICON Oxford Foot Model, and intersegmental coordination was analyzed using a modified vector coding technique. Results: The results showed that coordination patterns varied significantly between the ascending and descending phases and across the early, middle, and late periods. In the early ascending phase, knee extension exhibited in-phase coordination (shank external rotation with hindfoot inversion), resembling propulsion-related coordination in gait, whereas knee flexion displayed greater anti-phase coordination between hindfoot plantar flexion and forefoot dorsiflexion. The middle and late periods demonstrated heel-rise-specific patterns, with coordination shifting from proximal to distal dominance. Knee flexion altered the coordination between the shank and hindfoot and between the hindfoot and forefoot in the sagittal plane compared to that during knee extension. Conclusions: These findings suggest that the knee position influences intersegmental coordination during heel rises, and the present results provide reference values that can enable future diagnostic validation and comparative studies in pathological populations.

Biomechanics doi: 10.3390/biomechanics5040086

Authors: Sean P. Flanagan

Background/Objectives: Decreased ankle dorsiflexion range of motion (DFROM) is thought to negatively impact lower extremity flexion patterns, which use the coordinated flexion of the hips, knees, and ankles in activities such as the eccentric phase of a squat and landing from a jump. However, the results from experiments using human subjects to ascertain the relationship between DFROM and the mechanics of these flexion patterns are not clear. The purpose of this study was to elucidate the relationship between DFROM and the depth of the flexion pattern via computer simulations. Methods: The human body was represented as a planar model with four segments connected by three revolute joints. The ankle, knee, and hip angles that feasibly achieve three depths (25%, 50%, and 75% of the model’s leg length) were determined, and solutions that did not satisfy the constraints to create a realistic flexion pattern were removed. Results: There were a large number of solutions at each depth, but the number of solutions decreased with increasing depth. For a given depth, increasing DFROM required an increase in knee flexion and a decrease in hip flexion. Increasing depth required an increase in all three flexion angles. The relationships between joint angles and depth and between joint angles for a given depth were significant, but the standard errors of the estimate and the coefficients of variation were large. Conclusions: The relationship between DFROM and lower extremity flexion depth is obscured by the multiple combinations of ankle, knee, and hip angles that can achieve a particular depth and their interdependencies.

Biomechanics doi: 10.3390/biomechanics5040085

Authors: Boryi A. Becerra-Patiño Juan D. Paucar-Uribe Carlos F. Martínez-Benítez Valeria Montilla-Valderrama Armando Monterrosa-Quintero Adriana Guzmán Sánchez

Background: Some studies have suggested that physical fitness and body composition may influence individual and collective performance. However, it is necessary to be able to define the relationships between these variables in soccer players of different ages. Objective: To determine the relation between physical fitness level, body composition, and somatotype in female youth soccer players in response to age. Materials and methods: A total of 56 players were evaluated: 19 early adolescents (EA–U13) with a body mass of 48.35 ± 5.67 kg and a height of 157.63 ± 5.55 cm, 21 middle adolescents (MA–U15) with a body mass of 54.02 ± 5.96 kg and a height of 160.37 ± 5.25 cm and 16 late adolescents (LA–U17) with a body mass of 55.37 ± 6.15 kg and a height of 162.39 ± 5.77 cm. The physical fitness tests were: Squat Jump (SJ), Countermovement Jump (CMJ), Countermovement Jump with Arms (CMJA), Single Leg Countermovement Jump, COD-Timer 5-0-5, COD-Timer 5+5, Speed 15 m, Hamstring Strength, and Running-Based Anaerobic Sprint Test (RAST). The International Society for the Advancement of Kinanthropometry (ISAK) protocols were used to determine anthropometric measurements (skinfolds, circumferences, bone diameters), and the Heath-Carter method was used to assess body composition and somatotype, with z-scores calculated using the Phantom strategy. Results: The analysis revealed that the most significant differences between groups were observed in general anthropometric measurements (ω2 = 0.84), followed by sitting height (ω2 = 0.51) and percentage of body fat according to Carter’s method (ω2 = 0.24), all with large and statistically significant effect sizes (p < 0.05). Larger muscle and bone dimensions, especially in the hip, thigh, and calf, are closely related to better strength, power, and initial sprint speed performance in female soccer players. Conclusions: This study reaffirms that muscle mass is a key predictor of athletic performance, along with strength at high speeds, promoting improvements in power and sprinting in the initial meters. Adiposity is a limiting factor for youth soccer players. Age progression and biological maturation favor the development of the mesomorphic profile, optimizing strength and power.

Biomechanics doi: 10.3390/biomechanics5040084

Authors: Kinga Wiktoria Łosińska Artur Gołaś Florentyna Tyrała Monika Szot Adam Maszczyk

Background/Objectives: This study examined the effects of a six-week eccentric–reactive training program on neuromechanical markers of lateral explosiveness, asymmetry, and stretch-shortening cycle (SSC) efficiency in elite male youth table tennis players. Fourteen national-level athletes (mean age = 16.6 years) were assigned to either an experimental group (EG, n = 7) or a control group (CG, n = 7). EG performed flywheel squats and lateral depth jumps three times per week, while CG maintained regular training. Pre- and post-intervention testing included countermovement jumps, reactive strength index (RSI_DJ), force asymmetry, time-to-stabilization, SSC efficiency, and energy transfer ratio (ETR), measured via force plates, EMG, and inertial sensors. Methods: Multi-dimensional statistical analysis revealed coordinated improvements in explosive power and movement efficiency following eccentric training that were not visible when examining individual measures separately. Athletes in the training group showed enhanced neuromechanical control and developed more efficient movement patterns compared to controls. The analysis successfully identified distinct performance profiles and demonstrated that the training program improved explosive characteristics in elite table tennis players. Results: Univariate ANOVAs showed no significant Group × Time effects for RSI_DJ, ETR, or SSC_Eff, although RSI_DJ displayed a moderate effect size in EG (d = 0.47, 95% CI [0.12, 0.82], p = 0.043). In contrast, MANOVA confirmed a significant multivariate Group × Time interaction (p = 0.013), demonstrating integrated neuromechanical adaptations. Regression analysis indicated lower baseline CMJ and RSI_DJ predicted greater RSI improvements. Conclusions: In conclusion, eccentric–reactive training promoted multidimensional neuromechanical adaptations in elite racket sport athletes, supporting the use of integrated monitoring and targeted eccentric loading to enhance lateral explosiveness and efficiency.

Biomechanics doi: 10.3390/biomechanics5040083

Authors: Pablo Santana Prata Felipe J. Aidar Taísa Pereira Santos Ângelo de Almeida Paz Sarah Lisia da Silva Paixão Rozani Cristina Alves Osvaldo Costa Moreira Pantelis T. Nikolaidis

Introduction: Paralympic powerlifting (PP) is a sport in which the bench press is the sole exercise. Warm-up routines are considered essential for optimal performance. Objectives: This study aims to analyze different types of warm-up protocols—traditional warm-up (TW), post-activation performance enhancement (PAPE), and without warm-up (WW)—and their effects on dynamic strength indicators, core temperature, and skin temperature in athletes with disabilities. Methods: Fourteen nationally ranked PP athletes participated in the study. Their performance was evaluated following different warm-up protocols. Dynamic variables analyzed included Maximum Velocity (VMax), Mean Propulsive Velocity (MPV), and Power output. Additionally, tympanic and skin temperatures were measured. Results: No significant differences were observed in dynamic strength indicators across the different warm-up protocols. Thermographic analysis revealed differences only in the triceps muscle between PAPE and TW (p < 0.001), TW and WW (p = 0.004), and PAPE and WW (p = 0.015). Differences were also observed between TW and WW (p = 0.026). Ten minutes post-warm-up, differences were noted between PAPE and WW (p < 0.001) and between TW and WW (p = 0.001). In the WW condition, significant differences were found between pre-warm-up and 10 min post-warm-up (p = 0.031), as well as between post-warm-up and 10 min later (p = 0.003). Conclusions: The study evaluated the potential impact of warm-ups on dynamic indicators of strength, core temperature, and skin temperature. No differences were found between the warm-up methods for strength indicators. Regarding skin temperature, only the triceps showed differences between the PAPE and Traditional methods. Regarding core temperature, after warm-up and 10 min later, the methods without warm-up showed higher temperatures than the PAPE and Traditional methods. Therefore, in practical applications, warm-up methods do not appear to interfere with strength indicators, with lower skin temperatures for the triceps in the PAPE methods.

Biomechanics doi: 10.3390/biomechanics5040082

Authors: Cecilia Lo Zoppo Valeria Belluscio Giuseppe Vannozzi

Background/Objectives: The 2-minute walk test (2MWT) is a time-based gait assessment commonly employed for populations with limited walking ability for greater tolerability compared to the longer 6-minute test. The recommended distance to perform the tests is a 30 m straight path, a space requirement that is not always available in non-laboratory contexts. Shorter paths are therefore often adopted, but associated changes in gait patterns are not clear. The aim of the study is therefore to investigate how different walking path lengths affect gait patterns during the 2MWT. Methods: Twenty healthy young adults performed three walking trials on a straight hallway of 5 m, 15 m, and 30 m lengths. Spatiotemporal gait parameters were measured using three inertial measurement units on both distal tibiae and at pelvis level. Results: The 5 m path showed the greatest deviations, specifically in walking distance, walking speed, stride duration, stance time, swing time, single support time, and cadence, if compared to longer distances (p < 0.05). The 15 m path showed differences only in walking distance and walking speed (p < 0.05), if compared to the 30 m path. Conclusions: Shorter path lengths, particularly the 5 m, significantly impact gait patterns and should be considered when interpreting 2MWT results in clinical settings. The 30 m path is recommended as the gold standard, with 15 m as a viable alternative for assessing temporal parameters. Nevertheless, the extent to which each feature would be over/underestimated when walking in limited spaces is also addressed.

Biomechanics doi: 10.3390/biomechanics5040081

Authors: Li Jin Brandon Yang

Background/Objectives: Understanding how muscle fatigue contributes to musculoskeletal injuries is critical in sports science. Although joint biomechanics during landing under fatigue has been studied before, limited research has focused on the layup phase under fatigue. This study examined the effects of fatigue on ankle, knee, and hip-joint biomechanics during layup and landing. We hypothesized that fatigue would increase peak vertical ground reaction force (GRF), peak knee extension angle, and peak joint moments. Methods: Fourteen healthy male participants performed 3-step layups and drop landings using their dominant leg on force plates. The fatigue protocol consisted of squat jumps, step-ups, and repeated countermovement jumps (CMJs), with fatigue defined as three consecutive CMJs below 80% of the participant’s pre-established maximum jump height. After a fatigue protocol, they repeated the tasks. Kinematic data were collected using an eight-camera Vicon system (100 Hz), and GRF data were recorded with two AMTI force plates (1000 Hz). Thirty-six reflective markers were placed on lower-limb anatomical landmarks, and data were processed using Visual 3D. Paired t-tests (α = 0.05) were conducted using SPSS (V26.0) to compare pre- and post-fatigue outcomes. Results: Significant increases were found in peak GRF during landing (pre: 3.41 ± 0.81 BW [Body Weight], post: 3.95 ± 1.05 BW, p = 0.036), and peak negative hip joint work during landing (pre: −0.34 ± 0.18 J/kg, post: −0.66 ± 0.43 J/kg, p = 0.025). Conclusions: These findings indicate that fatigue may alter landing mechanics, reflected in increased ground reaction forces and negative hip joint work. These preliminary findings should be interpreted cautiously, and future studies with larger samples and additional neuromuscular measures under sport-specific conditions are needed to improve ecological validity.

Biomechanics doi: 10.3390/biomechanics5040080

Authors: Omid Jahanian Barbara Silver-Thorn Vaishnavi Muqeet Elizabeth T. Hsiao-Wecksler Brooke A. Slavens

Objectives: To quantify the effects of geared wheelchair wheels on energy expenditure during manual wheelchair propulsion in individuals with spinal cord injury (SCI). Methods: Eleven adult manual wheelchair users with SCI propelled their personal manual wheelchairs, which were equipped with a pair of geared wheels, on a passive wheelchair ergometer in low-gear and standard-gear conditions for six minutes. The energy cost of transport, distance traveled, rate of oxygen consumption (SCI MET), rate of perceived exertion, heart rate, and stroke cycle frequency were measured and compared across the gear conditions. Results: The distance traveled and SCI MET were significantly lower (p = 0.003) and cost of transport was significantly higher under the low-gear condition compared with the standard-gear condition. Gear condition exerted a moderate effect on the level of exertion; however, the decrease in the rate of perceived exertion under the low-gear condition was not statistically significant. Gear condition did not significantly affect heart rate and stroke cycle frequency. Conclusions: Geared manual wheelchair propulsion was significantly more energy-demanding, but less intense (easier) under the low-gear condition than the standard-gear condition. Using geared wheels may be beneficial for manual wheelchair users to independently accomplish strenuous propulsion tasks during typical activities of daily living, such as propulsion on carpeted floor. However, the small sample size and inclusion of only male participants limit the generalizability of these findings, and future studies with larger and more diverse cohorts are warranted.

Biomechanics doi: 10.3390/biomechanics5040079

Authors: Đorđe Brašanac Marko Kapeleti Igor Zlatović Miloš Ubović Vladimir Mrdaković

Background: Previous research has identified center of mass vertical oscillation and leg stiffness as the most common variables differentiating Natural and Groucho running techniques. The aim was to assess the inter-session reliability and inter-technique sensitivity of synchronized inertial measurement units and contact grids in quantifying kinematic and kinetic differences between Natural and Groucho running techniques. Methods: Eleven physically active and healthy males ran at a speed 50% higher than transition speed. Two sessions for Natural and two for Groucho running were performed, each lasting 1 min. Results: Most variables exhibited a similar inter-session reliability across running techniques, except contact time and center of mass vertical displacement, ranging from moderate to good (ICC = 0.538–0.897). A statistically significant difference between running techniques was found for all variables (p < 0.05), except for contact time and center of mass vertical oscillation (p > 0.05), likely due to inconsistency in reliability depending on the running technique, which may have covered the underlying differences. Conclusions: We can conclude that the combination of synchronized inertial measurement units and contact grids showed potentially acceptable reliability and sufficient sensitivity to recognize and differentiate between Natural and Groucho running techniques. The results may contribute to a broader understanding of the differences between these two running techniques and encourage the increased use of these devices within therapeutic, recreational, and sports running contexts.

Biomechanics doi: 10.3390/biomechanics5040078

Authors: Jorge Pérez-Contreras Rodrigo Villaseca-Vicuña Esteban Aedo-Muñoz Felipe Inostroza-Ríos Ciro José Brito Alejandro Bustamante-Garrido Guillermo Cortés-Roco Juan Francisco Loro-Ferrer Pablo Merino-Muñoz

Background/Objectives: To compare the external load (EL) of elite youth soccer players during official international matches between age categories and playing positions. Methods: The sample consisted of 42 elite youth soccer players categorized by age categories, U-15, U-17 and U-20 and playing positions: central defender (CD); fullback (FB); midfielder (MF); wide attacker (WA) and striker (ST). The Vector X7 (Catapult Sports) device was used for collecting the following EL variables: total distance traveled (TD), player load (PL) and distance traveled per velocity band 0 to 7 km/h (D7); 7 to 13 km/h (D13); 13 to 19 km/h (D19); 19 to 23 km/h (D23) and >23 km/h (HSR). Linear mixed-effect models were applied to analyze the differences. Results: Large differences were found between positions (p < 0.01) in TD (η2p = 0.48), PL (η2p = 0.30), D19 (η2p = 0.44), D23 (η2p = 0.68) and HSR (η2p = 0.53). Large differences were found according to category between U-15 and U-17 in TD (p = 0.006 and η2p = 0.25) and D13 (p = 0.003 and η2p = 0.27). Large interaction effects were found in DT (p = 0.014 and η2p = 0.44) and D23 (p = 0.002 and η2p = 0.51). Conclusions: This study concludes that there are differences in EL in official matches in elite youth players between age categories and playing position. These differences can be applied in practice to design individualized training by playing position and to monitor EL during microcycles.

Biomechanics doi: 10.3390/biomechanics5040077

Authors: Monique Mokha Jack Stensland Andrew Schafer Sean McBride

Background/Objectives: National Football League (NFL) American football players are exposed to osteoarthritis risk factors of obesity and high joint loads. We sought to examine the association between total body mass (TBM), lean body mass (LBM), body fat percentage (BF%), and normalized compressive knee joint reaction forces (JRFcomp), peak knee adductor moments (KAM), and vertical ground reaction forces (vGRF) in NFL draft-eligible players during a high-speed run. Methods: A total of 125 participants ran a single trial at 5.5–6.5 m/s for 5 s on an instrumented treadmill. Bilateral vGRF and knee joint kinetics were calculated using inverse dynamics. Body composition was assessed using bioelectrical impedance. Results: LBM demonstrated significant moderate associations with vGRF (left, r(123) = −0.56, p < 0.001; right, r(123) = −0.60, p < 0.001) and low-to-negligible associations with KAM (left, r(123) = −0.20, p = 0.026; right, r(123) = −0.30, p < 0.001) and JRFcomp (left, r(123) = −0.39, p = 0.020; right, r(123) = −0.38, p = 0.015), respectively. TBM showed significant moderate negative associations with vGRF (left, r(123) = −0.56, p < 0.001; right, r(123) = −0.61, p < 0.001) and low-to-negligible associations with KAM (left, r(123) = −0.21, p = 0.021; right, r(123) = −0.28, p = 0.002) and JRFcomp (left, r(123) = −0.39, p < 0.001; right, r(123) = −0.37, p < 0.001), respectively. BF% showed significant low-to-negligible negative associations with JRFcomp (left, r(123) = −0.21, p < 0.001; right, r(123) = −0.22, p < 0.001) and vGRF (left, r(123) = −0.39, p < 0.001; right, r(123) = −0.41, p < 0.001), respectively, and no significant associations with KAM, p > 0.05. The heavier group exhibited significantly lower normalized JRFcomp, and vGRF, p < 0.05. Conclusions: Heavier, but not fatter, players attenuate knee loads. Dampening may be a short-term protective strategy for joints of heavier players.

Biomechanics doi: 10.3390/biomechanics5040076

Authors: Ourania Ntousi Maria Roumpi Panagiotis K. Siogkas Demosthenes Polyzos Ioannis Kakkos George K. Matsopoulos Dimitrios I. Fotiadis

Background/Objectives: The process of designing and fabricating bone tissue engineering scaffolds is a multi-faceted and intricate process. The scaffold is designed to attach cells to the required volume of regeneration to subsequently migrate, grow, differentiate, proliferate, and consequently develop tissue within the scaffold which, in time, will degrade, leaving just the regenerated tissue. The fabrication of tissue scaffolds requires adapting the properties of the scaffolds to mimic, to a large extent, the specific characteristics of each type of bone tissue. However, there are some significant limitations due to the constrained scaffolds’ architecture and structural features that inhibit the optimization of bone scaffolds. Methods: To overcome these shortcomings, new computational approaches for scaffold design have been adopted through currently adopted computational methods such as finite element analysis (FEA), computational fluid dynamics (CFD), and fluid–structure interaction (FSI). Results: This paper presents a narrative review of the state of the art in the field of parametric numerical modeling and computational fluid dynamics geometry-based models used in bone tissue engineering. Computational methods for scaffold design improve the process of constructing scaffolds and contribute to tissue engineering. Conclusions: This paper highlights the benefits of computational methods on employing scaffolds with different architectures and inherent characteristics that can potentially contribute to a favorable environment for hosting cells and predict their behavior and response. By recognizing these benefits, researchers can enhance and optimize scaffold properties for future advancements in tissue engineering research that will lead to more accurate and robust outcomes.

Biomechanics doi: 10.3390/biomechanics5040075

Authors: Milosz Mielniczek Patrick Lunde Roland van den Tillaar

Background/Objectives: This study aimed to examine the effects of an eight-week wearable resistance (WR) training program on jump performance and jump kinematics in experienced senior female volleyball players. It was hypothesised that using WR would increase training load, thereby enhancing vertical jump performance and influencing kinematic movement patterns. Methods: Sixteen competitive female volleyball players (mean age: 23.5 ± 3.24 years; mean weight: 66.8 ± 6.9 kg; mean height: 174.7 ± 5.8 cm) participated in the study. Participants were randomly assigned to either a control group (n = 8) or an intervention group (n = 8) that trained with calf-mounted WR. The intervention group performed supervised resistance training sessions twice per week for eight weeks, totalling 16 sessions. Jump performance was assessed using an Infrared Optical Contact Grid (MuscleLab, Ergotest Innovation AS, Norway), and jump kinematics were measured with the Xsens Link motion capture system (Movella, The Netherlands). Results: The WR group demonstrated a statistically significant improvement in vertical jump height (p = 0.031), with no significant changes in kinematic variables. The control group, however, showed a significant increase in T8–pelvis flexion during the countermovement jump (CMJ) following the intervention period. Conclusions: Eight weeks of WR training can improve CMJ performance in-season among experienced female volleyball players without affecting movement kinematics. Future research should investigate optimal loading strategies and long-term adaptations. These findings suggest that integrating small wearable loads into regular volleyball practice can help athletes maintain and improve explosive performance without disrupting normal training routines.

Biomechanics doi: 10.3390/biomechanics5040074

Authors: Manoel Rios Ricardo J. Fernandes Ricardo Cardoso Pedro Fonseca João Paulo Vilas-Boas José António Silva

Background/Objectives: This study aimed to investigate the anthropometric characteristics, motor performance, and isokinetic strength profiles of elite Portuguese female handball players, as well as to examine the relationships among these variables. Methods: Sixteen national-team female handball players with an average age of 20.25 ± 0.45 years, height of 171.13 ± 8.13 cm and body mass of 72.24 ± 10.96 kg volunteered. Evaluations were conducted in two sessions within one week (24–48 h apart). The first comprised anthropometric and motor performance tests, while the second focused on isokinetic strength assessments of the upper and lower limbs. Pearson correlations assessed variable associations (p < 0.05). Results: Direct correlations were found between height and arm span (r = 0.910) and between internal rotation total work and internal rotation average power (r = 0.960). The 9 m jump throw was associated with the 7 m standing throw (r = 0.670). External rotation peak torque correlated with squat jump performance (r = 0.540) and the 7 m standing throw (r = 0.760) and 9 m jump throw (r = 0.568). Internal rotation peak torque associated with squat jump performance (r = 0.674) and the 7 m standing throw (r = 0.550). Knee extension peak torque correlated with squat jump performance (r = 0.650), while knee extension total work was strongly associated with external rotation total work (r = 0.870). Knee flexion total work was associated with knee flexion peak torque (r = 0.910). Conclusions: The integrated analysis of anthropometric, motor and isokinetic variables revealed distinct strength–performance associations in female handball players, highlighting the role of upper- and lower-limb muscle function in jumping and throwing.

Biomechanics doi: 10.3390/biomechanics5040073

Authors: Jason Wicke Jordan L. Cola Hannah Panzarella

Background/Objectives: Long-distance running often requires athletes to carry their own hydration. Both the velocity of the runner and the load will affect the ground reaction forces (GRFs). Furthermore, carrying a liquid mass may have different outcomes on GRF compared to carrying a solid mass. This effect may in turn potentially result in a greater risk of injury. The goal of this study was to examine the GRF while jogging with different quantities of water in a hydration pack. It was expected that GRF measures would change with increased hydration pack weight. Methods: Twenty college-aged participants were asked to run over a force plate with an empty hydration pack and packs (0.71 kg) filled with 0.5 litres (1.21 kg), 1.5 litres (1.71 kg), and 2.5 litres (3.21 kg) of water. Results: No significant differences (p > 0.05) in the vertical, lateral, or forward–back measures were found between the different loads. These outcomes may be a result of the dampening effect the movement of the water may have on gait. Conclusions: It is believed that the benefit of having hydration readily available via a hydration pack will outweigh any potential for injury due to the added weight being carried.

Biomechanics doi: 10.3390/biomechanics5040072

Authors: Cyanea Davies Alina P. Swafford Tedd Girouard Keoni Kins John A. Mercer

Body weight support (BWS) reduces joint loading but also lowers muscle activation during walking, while blood flow restriction (BFR) increases muscle activation and metabolic stress during low-intensity exercise. Although both interventions are used in rehabilitation settings, their combined effects on neuromuscular responses during locomotion have not been studied. The purpose of this study was to determine whether muscle activity of the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), gastrocnemius (GA), and stride frequency (SF) were influenced by an interaction between BWS and BFR. Methods: Seven healthy participants (three men and four women; 23.7 ± 3.0 years; 171.3 ± 6.9 cm; 64.4 ± 4.94 kg) completed four walking conditions at 0% and 50% BWS with and without 80% occlusion pressure of BFR at a self-selected speed. Electromyography (EMG) was recorded for 30s during each condition. Results: EMG was not influenced by interaction between BWS and BFR for RF (p = 0.761), BF (p = 0.845), TA (p = 0.684), GA (p = 0.129), or SF (p = 0.345). Furthermore, RF (p = 0.479), BF (p = 0.639), TA (p = 0.684), GA (p = 0.404), and SF (p = 0.161) were influenced by the main effect of BFR. RF (p = 0.102), BF (p = 0.675), TA (p = 0.900), and SF (p = 0.740) were influenced by the main effect of BWS. However, GA was influenced by BWS regardless of BFR (p = 0.039). Conclusions: The combination of an acute application of BFR and BWS did not influence lower extremity muscle activity when walking at a self-selected pace. Further research is needed to continue to explore the neuromuscular responses to the combination of BFR and BWS under varying levels of BFR application, BWS, and walking speeds.

Biomechanics doi: 10.3390/biomechanics5040071

Authors: Sylvana Minkes-Weiland Han Houdijk Heleen A. Reinders-Messelink Luc H. V. van der Woude Paul P. Hartman Rob den Otter

Background/Objectives: Swing leg resistance may stimulate propulsive force, required for forward progression and leg swing, in post-stroke patients. To assess the potential of swing leg resistance in rehabilitation, more knowledge is needed on how this unilateral manipulation affects gait. Therefore, we explored the bilateral effects of a unilateral swing leg resistance on muscle activity, kinematics, and kinetics of gait in able-bodied individuals. Methods: Fourteen able-bodied participants (8 female, aged 20.7 ± 0.8 years, BMI 23.5 ± 1.9) walked on an instrumented treadmill at 0.28 m/s, 0.56 m/s, and 0.83 m/s with and without unilateral swing leg resistance provided by a weight (0 kg, 0.5 kg, 1.25 kg, and 2 kg) attached to the leg through a pulley system. Propulsion and braking forces, swing time, step length, transverse ground reaction torques, and muscle activity in the gluteus medius (GM), biceps femoris (BF), rectus femoris (RF), vastus medialis (VM), medial gastrocnemius (MG), and soleus (SOL) were compared between conditions. Statistical analyses were performed using repeated measures ANOVAs, with a significance level of 5%. Results: Peak propulsive force and propulsive duration increased bilaterally, while peak braking force decreased bilaterally with unilateral swing leg resistance. In addition, the swing time of the perturbed leg increased with swing leg resistance. Muscle activity in the perturbed leg (GM, BF, RF, VM, MG) and the unperturbed leg (GM, BF, VM, MG, SOL) increased. Only in the BF (perturbed leg, late swing) and MG (unperturbed leg, early stance) did the muscle activity decrease with swing leg resistance. No adaptations in step length and transverse ground reaction torques were observed. Specific effects were enhanced by gait speed. Conclusions: Unilateral swing leg resistance can evoke effects that might stimulate the training of propulsion. A study in post-stroke patients should be conducted to test whether prolonged exposure to unilateral swing leg resistance leads to functional training effects.

Biomechanics doi: 10.3390/biomechanics5030070

Authors: Alex Ojeda-Aravena Rafael Lima Kons Eduardo Báez-San Martín Jairo Azócar-Gallardo Xurxo Dopico-Calvo

Background. In taekwondo (TKD), high-intensity actions—particularly kicks and rapid changes of direction—are key determinants of sport-specific performance. Kinetic vari-ables derived from unloaded countermovement jumps (CMJs) are employed as proxies of neuromuscular efficiency. However, most studies have examined the link between CMJ outputs and TKD using jump height alone in sport-specific tasks. Objective. To determine the associations between unloaded CMJ-derived kinetic variables and sport-specific performance, identifying key determinants of repeated high-intensity kicking capacity and change-of-direction ability. Methods. Fifteen national-team athletes (nine men, six women; 18–27 years) completed unloaded CMJ testing (Day 1) and, after 48 h, the Taekwondo-Specific Agility Test (TSAT) and the Multiple Frequency Speed of Kick Test (FSKTMULT) (Day 2). Results. For FSKTMULT, jump height (r = 0.545–0.746), take-off velocity (r = 0.548–0.799), and mean power (r = 0.602–0.799) were positively correlated with the number of kicks across all sets (p = 0.001–0.044). Stepwise regression identified mean power as the sole significant predictor, explaining 32–46% of the variance across sets. For TSAT, time correlated negatively with mean power (r = −0.678, p = 0.008), mean force (r = −0.536, p = 0.048), and RFD (0–30%) (r = −0.655, p = 0.011). Mean power and mid-propulsion impulse (30–60%) jointly explained 72.8% of the variance in TSAT time (R2 = 0.728, p < 0.001). Conclusions. Unloaded CMJ mean power and mid-propulsion impulse (30–60%) emerge as proxies of neuromuscular efficiency linked to sport-specific perfor-mance, supporting their use for athlete monitoring and targeted training.

Biomechanics doi: 10.3390/biomechanics5030069

Authors: Liam J. Houlton Jeremy A. Moody Theodoros M. Bampouras Joseph I. Esformes

Background: Cluster sets (CSs) maintain velocity and power in compound movements by employing similar propulsion strategies or maintaining impulse through different mechanisms. This study aimed to explore the effect of four CS conditions on back squat (BS) propulsion and provide models for estimating changes in propulsion based on repetition and set number. Methods: Twenty male participants (age = 28.3 ± 3.1 years, stature = 1.74 ± 8.21 m, body mass = 84.80 ± 7.80 kg, BS 1RM = 140.90 ± 24.20 kg) completed four data collection sessions. Each session consisted of three sets of five repetitions at 80% 1RM BS with three minutes of unloaded inter-set rest, using varying intra-set rest intervals. Experimental conditions included 0 s (TRAD), 10 s (CS10), 20 s (CS20), and 30 s (CS30) inter-repetition rest, randomly assigned to sessions in a counterbalanced order. Ground reaction force data were collected on dual force platforms sampling at 1000 Hz, from which net propulsive impulse (JPROP), mean force (MF), and propulsion time (tPROP) were calculated. Conditions and sets were analysed using a 4 × 3 (CONDITION*SET) repeated-measures ANOVA to assess differences between conditions and sets, and linear mixed models (LMMs) were used to provide regression equations for each dependent variable in each condition. Results: The ANOVA revealed no significant interactions for any dependent variable. No main effects of CONDITION or SET were observed for JPROP. The main effects of CONDITION showed that MF was significantly lower in TRAD than CS20 (g = 0.757) and CS30 (g = 0.749). tPROP was significantly higher in TRAD than CS20 (g = 0.437) and CS30 (g = 0.569). The main effects of SET showed that MF was significantly lower in S2 (g = 0.691) and S3 (g = 1.087) compared to S1. tPROP was significantly higher in S2 (g = 0.866) and S3 (g = 1.179) compared to S1. LMMs for CS20 and CS30 revealed no significant effect (p > 0.05) between repetition or set number and dependent variables. Conclusions: The results suggest that CS20 and CS30 maintain JPROP by limiting MF and tPROP attenuation. This is less rest than that suggested by the previous literature, which may influence programming decisions during strength and power mesocycles to maximise training time and training density. LMMs provide accurate estimates of BS propulsive force attenuation when separating repetitions by up to 30 s, which may help practitioners optimise training load for long-term adaptations.

Biomechanics doi: 10.3390/biomechanics5030068

Authors: Jose I. Sanchez Mauricio Plaza Nicolas Echeverria

Background/Objectives: this study describes the development of a novel three-dimensional electrogoniometer for the quantitative assessment of knee mobility and stability during gait. The primary objective is to determine whether real-time measurements obtained during dynamic activity provide more clinically relevant information than traditional static assessments. Methods: the device employs angular position encoders to capture knee joint kinematics—specifically flexion, extension, rotation, and tibial translation—during locomotion. Data are transmitted in real time to an Android-based application, enabling immediate graphical visualization. A descriptive observational study was conducted involving healthy participants and individuals with anterior cruciate ligament (ACL) injuries to evaluate the device’s performance. Results: results showed that the electrogoniometer captured knee flexion-extension with a range of up to 90°, compared to 45° typically recorded using conventional systems. The device also demonstrated enhanced sensitivity in detecting variations in tibial translation during gait cycles. Conclusions: this electrogoniometer provides a practical tool for clinical assessment of knee function, enabling real-time monitoring of joint behavior during gait. By capturing functional mobility and stability more accurately than static methods, it may enhance diagnostic precision and support more effective rehabilitation planning in orthopedic settings.

Biomechanics doi: 10.3390/biomechanics5030067

Authors: Anthony Sharp Jonathon Neville Ryu Nagahara Tomohito Wada John Cronin

Multiple-hops performed horizontally in series effectively assess return-to-play readiness, as they mimic the propulsive and decelerative demands of sports. Movement strategy variables (kinetic variables) offer more insight into injury recovery than outcome-based measures (kinematic variables) like hop distance alone. This study focused on kinematic and kinetic variables to assess asymmetries during triple-hop (3-Hop) and quintuple-hop (5-Hop) tests with 44 male athletes from university sports clubs and teams. The aim was to determine the magnitude and potential direction of asymmetry and compare the sensitivity of kinematic and kinetic variables. Results showed mean kinematic asymmetries below 7.1% (range: 0.00 to 28.9%), while average kinetic asymmetries were as high as 38.8% (range: 0.0% to 95.4%). These findings suggest that kinetic variables are more sensitive in assessing movement strategy, providing more detailed insight into rehabilitation and return-to-play decisions. The study emphasizes the importance of considering both outcome and movement strategy variables in injury recovery. These results have practical applications for clinicians and coaches supporting those in return-to-play scenarios, as well as those addressing performance deficits, therefore offering valuable information to refine exercise prescriptions and athletic program design.

Biomechanics doi: 10.3390/biomechanics5030066

Authors: Tanner Thorsen Nuno Oliveira

Background: Increased hip-flexion gait (HFgait) has been shown to promote increased aerobic demands by increasing peak swing-phase hip-flexion angles while walking at comfortable speeds. Biomechanically, HFgait produces a gait pattern similar to walking, while removing the flight phase from running and reducing tibial accelerations. We sought to identify knee joint contact forces between HFgait and common exercise modalities, including running, walking, and cycling, across intensity levels. Methods: Ten healthy participants completed two bouts (low and high intensity) of four different exercises: treadmill running, walking, HFgait, and cycling. Tibiofemoral joint compressive force (TCF) was estimated using a static optimization-based approach. Results: Peak TCF was greater in running compared to HFgait, walking, and cycling; greater in HFgait compared to cycling; and greater in walking compared to cycling. The integral of TCF (iTCF) was greater in running compared to cycling, greater in HFgait compared to running, walking, and cycling, and greater in walking compared to running and cycling. Conclusions: HFgait produced lower knee joint loading than running, comparable joint loading to walking, and greater joint loading than cycling. Thus, HFgait may serve as an exercise modality for populations where joint loading is of particular concern, while achieving aerobic demands similar to running or increased functional demands compared to stationary cycling.

Biomechanics doi: 10.3390/biomechanics5030065

Authors: Anna Tsiakiri Spyridon Plakias Georgios Giarmatzis Georgia Tsakni Foteini Christidi Marianna Papadopoulou Daphne Bakalidou Konstantinos Vadikolias Nikolaos Aggelousis Pinelopi Vlotinou

Background/Objectives: Multiple sclerosis (MS) often leads to gait impairments, even in early stages, and can affect autonomy and quality of life. Traditional assessment methods, while widely used, have been criticized because they lack sensitivity to subtle gait changes. This scoping review aims to map the landscape of advanced gait analysis technologies—both wearable and non-wearable—and evaluate their application in detecting, characterizing, and monitoring possible gait dysfunction in individuals with MS. Methods: A systematic search was conducted across PubMed and Scopus databases for peer-reviewed studies published in the last decade. Inclusion criteria focused on original human research using technological tools for gait assessment in individuals with MS. Data from 113 eligible studies were extracted and categorized based on gait parameters, technologies used, study design, and clinical relevance. Results: Findings highlight a growing integration of advanced technologies such as inertial measurement units, 3D motion capture, pressure insoles, and smartphone-based tools. Studies primarily focused on spatiotemporal parameters, joint kinematics, gait variability, and coordination, with many reporting strong correlations to MS subtype, disability level, fatigue, fall risk, and cognitive load. Real-world and dual-task assessments emerged as key methodologies for detecting subtle motor and cognitive-motor impairments. Digital gait biomarkers, such as stride regularity, asymmetry, and dynamic stability demonstrated high potential for early detection and monitoring. Conclusions: Advanced gait analysis technologies can provide a multidimensional, sensitive, and ecologically valid approach to evaluating and detecting motor function in MS. Their clinical integration supports personalized rehabilitation, early diagnosis, and long-term disease monitoring. Future research should focus on standardizing metrics, validating digital biomarkers, and leveraging AI-driven analytics for real-time, patient-centered care.

Biomechanics doi: 10.3390/biomechanics5030064

Authors: Juan Sebastián Salgado Manrique Christian Cifuentes-De la Portilla

Limb amputation causes significant challenges for patients in achieving effective mobility and functionality through prosthetic limbs. The prosthetic socket plays a pivotal role in the success of rehabilitation. This review explores the current advancements in prosthetic socket design and fabrication, focusing on traditional techniques like casting and lamination, and emerging technologies such as 3D printing and computer-aided design (CAD). By comparing these methods, this review highlights the advantages, limitations, and suitability for different clinical needs. This article discusses the importance of pressure distribution in socket design, emphasizing the need to relieve pressure in sensitive areas to prevent skin complications. It also examines the materials used in socket fabrication, from high-density polymers to advanced composites, assessing their impact on patient comfort and prosthetic performance. Additionally, we discuss the challenges practitioners face in prosthetic care, particularly in low-resource settings, and propose potential solutions through innovative techniques and materials. Advancements in computational modeling improved socket design and validation, enhancing patient comfort and improving the overall biomechanical interaction between the prosthesis and the user. The manuscript concludes by identifying future research opportunities, particularly in personalized prosthetic design and the integration of smart materials, to further enhance the comfort, functionality, and accessibility of prosthetic sockets.

Biomechanics doi: 10.3390/biomechanics5030063

Authors: Sentong Wang Itsuki Fujita Koun Yamauchi Kazunori Hase

Background/Objectives: In recent years, 3D shape models of the human body have been used for various purposes. In principle, CT and MRI tomographic images are necessary to create such models. However, CT imaging and MRI generally impose heavy physical and financial burdens on the person being imaged, the model creator, and the hospital where the imaging facility is located. To reduce these burdens, the purpose of this study was to propose a method of creating individually adapted models by using simple X-ray images, which provide relatively little information and can therefore be easily acquired, and by transforming an existing base model. Methods: From medical images, anatomical feature values and scanning feature values that use the points that compose the contour line that can represent the shape of the femoral knee joint area were acquired, and deformed by free-form deformation. Free-form deformations were automatically performed to match the feature values using optimization calculations based on the confidence region method. The accuracy of the deformed model was evaluated by the distance between surfaces of the deformed model and the node points of the reference model. Results: Deformation and evaluation were performed for 13 cases, with a mean error of 1.54 mm and a maximum error of 12.88 mm. In addition, the deformation using scanning feature points was more accurate than the deformation using anatomical feature points. Conclusions: This method is useful because it requires only the acquisition of feature points from two medical images to create the model, and overall average accuracy is considered acceptable for applications in biomechanical modeling and motion analysis.

Biomechanics doi: 10.3390/biomechanics5030062

Authors: Sachini N. K. Kodithuwakku Arachchige Harish Chander Adam C. Knight

Concurrent cognitive tasks, such as avoiding visual, auditory, chemical, and electrical hazards, and concurrent motor tasks, such as load carriage, are prevalent in ergonomic settings. Trips are extremely common in the workplace, leading to fatal and non-fatal fall-related injuries. Intrinsic factors, such as attention, fatigue, and anticipation, as well as extrinsic factors, including tasks at hand, affect trip recovery responses. Objective: The purpose of this study was to investigate the ankle joint kinematics in unexpected and expected trip responses during single-tasking (ST), dual-tasking (DT), and triple-tasking (TT), before and after a physically fatiguing protocol among young, healthy adults. Methods: Twenty volunteers’ (10 females, one left leg dominant, age 20.35 ± 1.04 years, height 174.83 ± 9.03 cm, mass 73.88 ± 15.55 kg) ankle joint kinematics were assessed using 3D motion capture system during unperturbed gait (NG), unexpected trip (UT), and expected trip (ET), during single-tasking (ST), cognitive dual-tasking (CDT), motor dual-tasking (MDT), and triple-tasking (TT), under both PRE and POST fatigue conditions. Results: Greater dorsiflexion angles were observed during UT compared to NG, MDT compared to ST, and TT compared to ST. Significantly greater plantar flexion angles were observed during ET compared to NG and during POST compared to PRE. Conclusions: Greater dorsiflexion angles during dual- and triple-tasking suggest that divided attention affects trip recovery. Greater plantar flexion angles following fatigue are likely an anticipatory mechanism due to altered muscle activity and increased postural control demands.

Biomechanics doi: 10.3390/biomechanics5030061

Authors: Andrew H. Hunter Nicholas M. A. Smith Bella Bello Bitugu Austin Wontepaga Luguterah Robbie S. Wilson

Background/Objectives: In soccer, scanning before receiving the ball helps players better perceive and interpret their surroundings, enabling faster and more effective passes. Despite its importance, no standardized tests currently incorporate scanning actions into assessments of passing abilities. In this study, we test the reliability and validity of a battery of passing tests that assess a player’s ability to control and pass the ball while also scanning for the appropriate target. Methods: We designed three passing tests that reflect different scanning demands that are routinely placed upon players during matches. Using players from the first and reserve teams of two professional clubs in Ghana (Club A, first-team n = 11, reserve-team n = 10; Club B, first-team n = 16, reserve-team n = 17), we: (i) tested the repeatability of each passing test (intraclass correlations), (ii) assessed whether the tests could distinguish between first and reserve team players (linear mixed-effects model), and (iii) examined whether players who were better in the passing tests had higher performances in 3v1 Rondo possession games (linear models). Results: All passing tests were significantly repeatable (ICCs = 0.77–0.85). Performance was highest in the 120-degree test (30.11 ± 7.22 passes/min), where scanning was not required, and was lowest in the 360-degree test (25.55 ± 5.94 passes/min), where players needed to constantly scan behind them. When players were scanning through an arc of 180 degrees, their average performance was 27.41 ± 6.14 passes/min. Overall passing performance significantly distinguished first from reserve team players (β = −1.47, t (51) = −4.32, p < 0.001)) and was positively associated with 3v1 Rondo possession performance (R2 = 0.51, p < 0.001). Conclusions: Our results show that these passing tests are reliable, distinguish players across competitive levels, and correlate with performance in possession games. These tests offer a simple, ecologically valid way to assess scanning and passing abilities for elite players.

Biomechanics doi: 10.3390/biomechanics5030060

Authors: Ilias Keskinis Vassilios Panoutsakopoulos Evangelia Merkou Savvas Lazaridis Eleni Bassa

Background/Objectives: Sprinting is a fundamental locomotor skill and a key indicator of lower limb strength and anaerobic power in early childhood. The aim of the study was to examine possible differences in the step kinematic parameters and their contribution to sprint speed between children with different patterns of speed development. Methods: 65 prepubescent male and female track athletes (33 males and 32 females; 6.9 ± 0.8 years old) were examined in a maximal 15 m short sprint running test, where photocells measured time for each 5 m segment. At the last 5 m segment, step length, frequency, and velocity were evaluated via a video analysis method. The symmetry angle was calculated for the examined step kinematic parameters. Results: Based on the speed at the final 5 m segment of the test, two groups were identified, the maximum sprint phase (MAX) and the acceleration phase (ACC) group. Speed was significantly (p < 0.05) higher in ACC in the final 5 m segment, while there was a significant (p < 0.05) interrelationship between step length and frequency in ACC but not in MAX. No other differences were observed. Conclusions: The difference observed in the interrelationship between speed and step kinematic parameters between ACC and MAX highlights the importance of identifying the speed development pattern to apply individualized training stimuli for the optimization of training that can lead to better conditioning and wellbeing of children involved in sports with requirements for short-sprint actions.

Biomechanics doi: 10.3390/biomechanics5030058

Authors: Md. Sumon Rahman Tatsuru Yazaki Takanori Chihara Jiro Sakamoto

Objectives: The aim of this study was to evaluate the impact of four working heights on lumbar biomechanics during wall construction tasks, focusing on work-related musculoskeletal disorders (WMSDs). Methods: Fifteen young male participants performed simulated mortar-spreading and bricklaying tasks while actual body movements were recorded using Inertial Measurement Unit (IMU) sensors. Muscle activities of the lumbar erector spinae (ES), quadratus lumborum (QL), multifidus (MF), gluteus maximus (GM), and iliopsoas (IL) were estimated using a 3D musculoskeletal (MSK) model and measured via surface electromyography (sEMG). The analysis of variance (ANOVA) test was conducted to identify the significant differences in muscle activities across four working heights (i.e., foot, knee, waist, and shoulder). Results: Findings showed that working at foot-level height resulted in the highest muscle activity (7.6% to 40.6% increase), particularly in the ES and QL muscles, indicating an increased risk of WMSDs. The activities of the ES, MF, and GM muscles were statistically significant across both tasks and all working heights (p < 0.01). Conclusions: Both MSK and sEMG analyses indicated significantly lower muscle activities at knee and waist heights, suggesting these as the best working positions (47 cm to 107 cm) for minimizing the risk of WMSDs. Conversely, working at foot and shoulder heights was identified as a significant risk factor for WMSDs. Additionally, the similar trends observed between MSK simulations and sEMG data suggest that MSK modeling can effectively substitute for sEMG in future studies. These findings provide valuable insights into ergonomic work positioning to reduce WMSD risks among wall construction workers.

Biomechanics doi: 10.3390/biomechanics5030059

Authors: Chris Toland John Cronin Duncan Reid Mitzi S. Laughlin Jeremy L. Fleeks

Current rehabilitation protocols for transitioning patients to late-stage recovery, evaluating return-to-play (RTP) clearance, and assessing tendon characteristics exhibit significant heterogeneity. Clinicians frequently interpret and apply research findings based on individual philosophies, resulting in varied RTP criteria and performance expectations. Despite medical clearance, patients recovering from Achilles tendon (AT) injuries often exhibit persistent impairments in muscle volume, tendon structure, and force-generating capacity. Inconsistencies in assessment frameworks, compounded by a lack of quantitative data and the utilization of specific metrics to quantify certain strength characteristics (endurance, maximal, explosive, etc.) and standardized protocols, hinder optimal functional recovery of the plantar flexors during the final stages of rehabilitation and RTP. With this in mind, the aim of this integrative review was to provide an overview of AT rehabilitation, with particular critique around mid-stage strengthening and the use of the heel-raise assessment in milestoning rehabilitation progress. From this critique, new perspectives in mid-stage strengthening are suggested and future research directions identified.

Biomechanics doi: 10.3390/biomechanics5030057

Authors: Catarina Rocha João Lobo Marco Parente Dulce Oliveira

Background: The knee joint performs a vital function in human movement, supporting significant loads and ensuring stability during daily activities. Methods: The objective of this study was to develop and validate a subject-specific framework to model knee flexion–extension by integrating 3D gait data with individualized musculoskeletal (MS) and finite element (FE) models. In this proof of concept, gait data were collected from a 52-year-old woman using Xsens inertial sensors. The MS model was based on the same subject to define realistic loading, while the 3D knee FE model, built from another individual’s MRI, included all major anatomical structures, as subject-specific morphing was not possible due to unavailable scans. Results: The FE simulation showed principal stresses from –28.67 to +44.95 MPa, with compressive stresses between 2 and 8 MPa predominating in the tibial plateaus, consistent with normal gait. In the ACL, peak stress of 1.45 MPa occurred near the femoral insertion, decreasing non-uniformly with a compressive dip around –3.0 MPa. Displacement reached 0.99 mm in the distal tibia and decreased proximally. ACL displacement ranged from 0.45 to 0.80 mm, following a non-linear pattern likely due to ligament geometry and local constraints. Conclusions: These results support the model’s ability to replicate realistic, patient-specific joint mechanics.

Biomechanics doi: 10.3390/biomechanics5030056

Authors: Vilko Petrić Sanja Ljubičić Dario Novak

Background/Objectives: Vertical jump is considered a reliable and valid method of assessing the level of muscular power and coordination across one’s lifespan. The main aim of the present study was to establish sex- and age-normative data for vertical jump outcomes in pre-school children. Methods: We recruited 411 boys and girls aged 3−6 years from four major cities in Croatia and Slovenia. Vertical jump was assessed with two tests: countermovement jump (CMJ) without and with arm swing using a reliable and valid Optojump measuring platform. Data were presented for the 5th, 15th, 25th, 50th (median), 75th, 90th, and 95th percentile. Results: No significant differences were observed in multiple vertical jump outcomes between boys and girls. The mean values for CMJ without and with arm swing between boys and girls were as follows: contact time (1.4 vs. 1.4 s/1.8 vs. 1.7 s), flight time (0.32 vs. 0.31 s/0.33 vs. 0.32), height (12.3 vs. 12.2 cm/13.0 vs. 12.5 cm), power (9.4 vs. 9.5 W/kg/9.3 vs. 9.1 W/kg), pace (0.7 vs. 0.7 steps/s/0.6 vs. 0.6 steps/s), reactive strength index (RSI; 0.10 vs. 0.09 m/s/0.08 vs. 0.08 m/s), and verticality (2.5 vs. 2.3/1.9 vs. 1.9). A gradual increase in all measures according to ‘age’ was observed (p for trend < 0.05). No significant ‘sex*age’ interaction was observed (p > 0.05). Conclusions: This is one of the first studies to provide sex- and age-normative data for complete vertical jump outcomes in pre-school children. These data will serve as an avenue for monitoring and tracking motor development in this sensitive period.

Biomechanics doi: 10.3390/biomechanics5030055

Authors: Marta Carvalho João Milho

Background/Objectives: The simulation of human movement offers transformative potential for the design of medical devices, particularly in understanding the cause–effect dynamics in individuals with neurological or musculoskeletal impairments. This study presents a simulation-driven framework to determine the optimal ankle–foot orthosis (AFO) stiffness for mitigating the risk of ankle sprains due to excessive subtalar inversion during high-impact activities, such as landing from a free fall. Methods: We employed biomechanical simulations to assess the influence of translational stiffness on subtalar inversion control, given that inversion angles exceeding 25 degrees are strongly correlated with injury risk. Simulations were conducted using a musculoskeletal model with and without a passive AFO; the stiffness varied in three anatomical directions. A Design of Experiments (DoE) approach was utilized to capture nonlinear interactions among stiffness parameters. Results: The results indicated that increased translational stiffness significantly reduced inversion angles to safer levels, though direction–dependent effects were noted. Based on these insights, we developed a 4D visualization tool that integrates simulation data with an interactive color–coded interface to depict ”safe design” zones for various AFO stiffness configurations. This tool supports clinicians in selecting stiffness values that optimize both safety and functional performance. Conclusions: The proposed framework enhances clinical decision-making and engineering processes by enabling more accurate and individualized AFO designs.