Biomechanics, Volume 5, Issue 2 (June 2025) – 15 articles

This study investigated kinetic and physiological load characteristics of Self-Manual Resistance Training (SMRT) lat pulldown. SMRT lat pulldown is a training method in which practitioner generates resistance manually using their own muscular force by gripping a towel with both hands and pulling it outward in a horizontal direction. We analyzed shoulder and elbow joint moments in frontal plane (2D) and muscle activity levels of latissimus dorsi (LD), posterior deltoid (PD), biceps brachii (BB), and triceps brachii (TB) during 10 maximal-effort repetitions of SMRT lat pulldown in 11 resistance-trained men. For comparison, we also measured muscle activity levels during a machine lat pulldown for 10 reps at 75% 1 RM load in same participants. Peak shoulder adduction and elbow extension moments during SMRT lat pulldown were both approximately 70% MVC. Mean rectified EMG of LD was significantly greater during machine lat pulldown than SMRT lat pulldown, whereas that of PD was significantly greater during SMRT than machine version. Mean rectified EMG of TB was high during SMRT, and that of BB was high in machine version. SMRT lat pulldown appears to produce relatively large shoulder adduction and elbow extension moments, increasing PD and TB activation and limiting LD activation. Full article

As powerful actions commonly proceed goal scoring opportunities within soccer, enhancing powerful actions could be essential to optimize performance. There is a large body of evidence supporting the positive associations between maximal isometric mid-thigh pull force-generating qualities and jump performance. Objectives: The purpose of this study was to determine if relative maximal isometric force production can discriminate between higher- and lower-performing jumpers among professional and semi-professional soccer players. As such, it was hypothesized that stronger players would have a greater jump performance than weaker players. Methods: An observational cross-sectional research design was used to assess ballistic and isometric force production of the lower limbs across players from four professional and semi-professional soccer clubs during the pre-season period. Seventy-six professional male lower-league soccer players (mass: 82.5 ± 8.2 kg; height: 1.80 ± 0.07 m; age: 25.8 ± 4.3 years) performed three trials of the countermovement jump (CMJ) and isometric mid-thigh pull (IMTP) using force plates. Players were categorized as strong and weak using the group’s average IMTP relative peak force (33.41 N/kg). A series of one-way Bayesian independent t-tests were performed to determine the difference between strong and weak groups. Results: A large magnitude of difference was observed between strong and weak players for relative peak force (d [95% CI] = 2.53 [2.017–∞]), with strong evidence supporting the hypothesis (BF₁₀ = 2.698 × 10⁺¹⁴). There was moderate evidence to support the hypothesis that strong players (n = 37) had a greater modified reactive strength index (mRSI) and relative average braking force in comparison to weaker players (n = 39). All other evidence was weak, with trivial-to-small differences (d = 0.10–0.42) for jump height, jump momentum, propulsive force, force at minimum displacement, time to take off, and countermovement depth. Conclusions: Maximal relative strength has implications on jump performance, albeit not on the jump outcome. Stronger players performed the CMJ more efficiently when observing the mRSI, with a shorter time to take off, while producing greater average relative forces during the braking phase. This could have potential implications in the sporting environment when performing jumping tasks, where they can achieve a similar outcome over a shorter duration. Full article

Background: Gravity profoundly influences human locomotion. Studies examining the effects of hyper-gravity on gait have largely relied on added external mass, potentially confounding results with changes in inertia and center of mass. This study attempted to isolate the effects of increased gravitational load on kinematics and electromyography during walking at several different levels of load. Methods: Fifteen healthy adults were exposed to simulated gravitational loads ranging from 100% to 130% of body weight using a novel harness and spring-based system that increased weight without the addition of external mass and without altering limb inertia. Participants walked on a treadmill at a self-selected speed through incremental loading and unloading. Lower limb kinematics and electromyography data were recorded. Traditional measures of gait, as well as more dynamical measures, including angle–angle analysis and phase portraits, were examined. Results: Data demonstrated that a 130% load is sufficient to induce kinematic changes at the hip and knee; however, these changes become significant only during the transition from 130% to lower load levels. Ankle kinematics and electromyography appeared to be unaffected. Conclusions: These findings suggest that the presence of external mass and alterations in limb inertias should be considered seriously as independent variables in future loading studies, and that weight and mass may need to be considered as separate effectors during locomotion. This study also found that the act of loading and unloading elicit distinct responses in the joints of the lower extremities, as well as that it may induce an adaptative after-effect. Full article

Background/Objectives: Research examining mobility in older adults often utilizes spatiotemporal gait parameters obtained from computerized walkway systems like GAITRite (Franklin, NY, USA) and Zenometrics, LLC (Peekskill, NY, USA). However, such parameters can vary across these widely used software applications due to differences in algorithms and post-processing techniques, making it potentially unsuitable to pool parameters acquired from different applications. We aim to determine whether gait parameters obtained from GAITRite and processed using two software systems can be reliably pooled for use in studies with older adults. Methods: Baseline gait data from 193 older adults aged 64–94 years old were examined. The gait protocol consisted of normal walking (NW) and walk while talking (WWT) conditions in which participants were instructed to walk on computerized walkways containing embedded pressure sensors. The resulting walks were processed using both software applications to attain eight gait parameters recorded from the right foot (velocity, stride length, double support percentage, cadence, swing time, stance time, stride length standard deviation, and swing time standard deviation). Linear regressions adjusted for age and gender between GAITRite (version 4.7) and their respective PKMAS (ProtoKinetics Movement Analysis Software version 6.0; Zenometrics, LLC.) gait variables were run to determine agreement between variables across the two pieces of software. Results: Adjusted linear regression models revealed that gait parameters across software systems were significantly correlated in both the NW (β ranged from 0.87 to 1.02, p ≤ 0.01) and WWT conditions (β ranged from 0.94 to 1.01, p ≤ 0.01). Swing time variability in the NW condition showed a lower correlation (β = 0.87). Furthermore, intercepts for all parameters except for the double support percentage in the NW condition (intercept = 2.63, p ≤ 0.01) and WWT condition (intercept = 2.75, p = 0.02) and stance time in the WWT condition (intercept = 0.05, p = 0.04) were not significantly different from 0. Conclusions: The results provide support that commonly examined gait parameters from GAITRite and PKMAS can be pooled and analyzed for use in studies with older adults. However, caution should be taken when pooling swing time variability and double support percentage data. Full article

Introduction: Therapeutic footwear has been often prescribed in clinical practice for accommodating foot deformities and preventing the development of ulceration, yet scientific evidence is limited and outdated. This study aimed to investigate the effects of two types of Orthofeet therapeutic footwear in comparison to low-cost generic as well as participants’ own athletic shoes on plantar pressure as well as lower extremity kinematics and kinetics. Methods: Twenty healthy participants without foot disorders or pain walked at self-paced speeds under each of the four footwear conditions. In-shoe plantar pressures were measured using F-Scan, and the gait kinematics and kinetics in the sagittal plane were obtained. The foot was divided into eight anatomical zones and three combined zones (forefoot, mid-foot, and hind foot), with peak plantar pressures recorded in each zone. Results: The therapeutic footwear showed significantly greater ankle dorsiflexion during late midstance and less ankle plantar flexion during push-off than generic shoes. Similarly, larger ankle plantar flexor torques were shown when wearing therapeutic footwear. Therapeutic footwear modified the plantar pressure distribution, increasing the peak pressure under the big toe while slightly reducing the peak pressure under the medial heel. The participants’ own athletic shoes provided slightly distinct outcome measures yet comparable performance when compared to therapeutic footwear. Conclusions: This study suggests that therapeutic footwear offers some distinct biomechanical modifications compared with generic shoes. Future studies are needed to assess if these changes lead to meaningful clinical outcomes, such as reduced injury risk or improved foot health. Full article

Background/Objectives: Children continually learn and develop new motor skills towards mastery, resulting in varying movement patterns at different stages of motor competence. Understanding this progression and confidently recognising development delay requires synthesising the children’s biomechanics literature. Firstly though, we must understand the past research and the approaches used. This review aims to identify and map the approaches and sources of the current literature in biomechanically quantifying the gross motor movement of typically developing children. Methods: A systematic scoping review was conducted in accordance with the Joanna Briggs Institute methodology. A database search of MEDLINE (Ovid), Scopus (Elsevier), ProQuest, CINAHL (EBSCO), and Web of Science identified English, peer-reviewed research biomechanically quantifying the movement of healthy children aged 3–12 years. Results include a bibliometric analysis and narrative summary. Results: Overall, 171 papers were included, representing a range of fields including footwear, injury, development, exercise, and activity. Country of origin and funding sources were equally variable. Walking was the predominantly assessed gross motor movement in children, followed by jumping and running. Equipment and facilities often resulted in more artificial settings, and important factors such as footwear used, testing environment, and condition familiarity were rarely reported. Conclusions: The literature results from diverse disciplines, institutions, and funding sources, but inconsistent reporting of conditions hinders synthesis. Future research is recommended to transparently report participant characteristics, environment, and testing conditions and to implement more ecologically valid protocols. Recommendations from this review will improve the quality of future research on children’s movement. Full article

Background: Drug treatments for gait disorders in post-stroke patients aim to reduce muscular hyperactivity. The analysis of muscle activity is essential to help clinicians understand these disorders. This study aimed to quantify changes in muscle synergies before (PRE) and after (POST) a rectus femoris nerve block. Methods: Gait analysis of 8 post-stroke patients before and immediately after nerve block. Muscle synergies were quantified from electromyographic signals. We have selected the account for variance, which indicates the effectiveness of the synergies, the recruitment selectivity index, which indicates the degree of multiplexing of the synergies, and the recruitment consistency index, which indicates the variability of the synergy activations across gait cycles. Results: A decrease in Variance Account For (VAF) is observed, showing a lack of robustness of the underlying muscle synergies between PRE and POST. We also note that spatial and temporal primitives result in different Index of Recruitment Selectivity (IRS) but similar Index of Recruitment Consistency (IRC) for PRE vs. POST. This shows that the synergies’ activations remain consistent across cycles but are more distributed in POST than in PRE. Conclusions: The motor nerve block has not created new muscle synergies of the paretic limb during gait but indicates that there is flexibility in motor organization. This method of quantification may enable clinicians to assess the motor adaptation potential of their post-stroke patients. Full article

Background/Objectives: The conventional practice in clinical settings involves using multi-use surgical instrumentation (SI). However, there is a growing trend towards transforming these multi-use SIs into disposable surgical instruments, driven by economic and environmental considerations without considering the biomechanical aspects. This study focuses on redesigning an SI kit for implanting cervical spinal facet cages. Understanding the boundary conditions (forces, torques, and bending moments) acting on the SI during surgery is crucial for optimizing its design and materials. Therefore, this study aims to develop a measurement system (MS) to record these loads during implantation and validate it through in vitro testing. Methods: A combined numerical–experimental approach was used to design and calibrate the MS. Finite element analysis (FE) was used to optimize the geometry of the sensitive element of the MS. This was followed by the manufacturing phase using 3D printing and then by calibration tests to determine the stiffness of the system. Finally, the MS was used to measure the boundary conditions applied during SI use during in vitro tests on a cervical Sawbone spine. Results: After designing the measurement system (MS) via finite element analysis, calibration tests determined stiffness values of K_F = 1.2385 N/(µm/m) (axial compression), K_T = −0.0015 Nm/(µm/m) (torque), and K_B = 0.0242 Nm/(µm/m) (non-axial force). In vitro tests identified maximum loads of 40.84 N (compression) and 0.11 Nm (torque). Conclusions: This study developed a measurement system to assess surgical implant boundary conditions. The data will support finite element modeling, guiding the optimization of implant design and materials. Full article

Background: This technical note proposes a deep learning-based, few-shot automatic key point tracking technique tailored to sports biomechanics research. Methods: The present method facilitates the arbitrary definition of key points on athletes’ bodies or sports equipment. Initially, a limited number of video frames are manually digitized to mark the points of interest. These annotated frames are subsequently used to train a deep learning model that leverages a pre-trained VGG16 network as its backbone and incorporates an additional convolutional head. Feature maps extracted from three intermediate layers of VGG16 are processed by the head network to generate a probability map, highlighting the most likely locations of the key points. Transfer learning is implemented by freezing the backbone weights and training only the head network. By restricting the training data generation to regions surrounding the manually annotated points and training specifically for each video, this approach minimizes training time while maintaining high precision. Conclusions: This technique substantially reduces the time and effort required compared to frame-by-frame manual digitization in various sports settings, and enables customized training tailored to specific analytical needs and video environments. Full article

Background: Gait assessment is a complex task involving locomotion and balance control across all body segments, requiring a global analysis in the event of motor disorders. Among these are spinal disorders, where an understanding of spinal kinematics during walking is important to improve treatment decisions and outcomes. The technique of stereophotogrammetric motion analysis is currently the gold standard in this context. A new integrated protocol for whole-body kinematic gait analysis is proposed in this study, which takes into account the movements of the spine. Methods: A new protocol with 30 passive markers was developed to analyze gait. Of these markers, 22 implemented the Davis protocol for gait measurement, while the other 8 were placed onto the spine to record spinal movements. The protocol’s accuracy was assessed through comparisons of the constructive angles of a manikin replicating the human body and the angles measured with the optoelectronic system. An assessment of intra- and inter-operator repeatability and protocol usability was carried out by recruiting and applying the protocol in a population composed of ten subjects (mean age 17.36—SD 10.12) without any history of spine pathology. Results: The protocol was validated successfully. The validation accuracy was more than satisfactory: the measured RMSE was 1.2 ± 1° for the data collected with the optoelectronic system with respect to the manikin. The intra-operator repeatability was also good in the sagittal and frontal planes (average ICC > 0.867), and the inter-operator repeatability was moderate or good in all planes (average ICC > 0.77). The usability score obtained using the System Usability Scale was satisfactory (mean 74.75, SD 5.88). Conclusions: This study proposes a new protocol to assess total body kinematics, including the spine in its three main segments, during gait. The successful validation of this protocol in terms of reliability and usability allows for its subsequent clinical application. Full article

Background/Objectives: Groin and hip injuries are common in sport, and muscle weakness has been identified as an intrinsic risk factor. So, analyzing the strength of the hip musculature becomes important. To date, there are no hip adductor isometric strength tests on force platforms. This study aims to analyze the intra-test reliability of a hip adductor strength test using force platforms. Methods: The study sample comprised 13 male professional soccer players with an average age of 22.3 ± 3 years, body mass of 75.8 ± 5.4 kg, and height of 1.8 ± 0.1 m. Assessments were conducted on a uniaxial force platform. The variables analyzed are peak force (PF), rate of force development (RFD), and impulse. Intra-test reliability was evaluated using the coefficient of variation (CV), intraclass correlation coefficient (ICC), and Bland–Altman plots. Results: Acceptable levels of reliability were identified solely for the variable of peak force, with CV values of D = 5.7% for the dominant profile and ND = 5.4% for the non-dominant profile. Furthermore, moderate and good relative reliability were observed in peak force for the dominant (ICC = 0.706) and non-dominant (ICC = 0.819) profiles, respectively. However, the remaining time-related variables, RFD and impulse, did not achieve acceptable levels of absolute reliability (CV > 10%) and displayed poor to moderate relative reliability. Conclusions: In summary, PF during the hip adductor isometric strength test demonstrated acceptable absolute and commendable relative reliability. Conversely, the time-related variables, specifically RFD and impulse, yielded unsatisfactory absolute and relative reliability levels. Full article

Background/Objectives: Currently, there is no strong evidence to support interventions for medial tibial stress syndrome (MTSS), a common running injury associated with tibial loading. Vertical ground reaction force (vGRF) and axial tibial acceleration (TA) are the most common methods of estimating tibial loads, yet clinical recommendations for technique modification to reduce these metrics are not well documented. This study investigated whether changes to speed, cadence, stride length, and foot-strike pattern influence vGRF and TA. Additionally, machine-learning models were evaluated for their ability to estimate vGRF metrics. Methods: Sixteen runners completed seven 1 min trials consisting of preferred technique, ±10% speed, ±10% cadence, forefoot, and rearfoot strike. Results: A 10% speed reduction decreased peak tibial acceleration (PTA), vertical average loading rate (VALR), vertical instantaneous loading rate (VILR), and vertical impulse by 13%, 10.9%, 9.3%, and 3.2%, respectively. A 10% cadence increase significantly reduced PTA (11.5%), VALR (15.6%), VILR (13.5%), and impulse (3.5%). Forefoot striking produced significantly lower PTA (26.6%), VALR (68.3%), and VILR (68.9%). Habitual forefoot strikers had lower VALR (58.1%) and VILR (47.6%) compared to rearfoot strikers. Machine-learning models predicted all four vGRF metrics with mean average errors of 9.5%, 10%, 10.9%, and 3.4%, respectively. Conclusions: This study demonstrates that small-scale modifications to running technique effectively reduce tibial load estimates. Machine-learning models offer an accessible, affordable tool for gait retraining by predicting vGRF metrics without reliance on IMU data. The findings support practical strategies for reducing MTSS risk. Full article

Background/Objectives: The manual tuning of exoskeleton control parameters is tedious and often ineffective for adapting to individual users. Human-in-the-loop (HIL) optimization offers an automated approach, but existing methods typically rely on metabolic cost, which requires prolonged data collection times of at least 60 s. Surface electromyography (EMG) signals, as an alternative, enable faster optimization with reduced data acquisition times. Methods: This study develops a rapid EMG-based HIL Bayesian optimization framework to tune hip exoskeleton controllers for assisting free leg swinging. Eight participants are asked to perform leg swinging at two frequencies with assistance from a hip exoskeleton. EMG signals from four sensors, representing muscle activity during forward and backward swings, are dynamically processed into cost functions. Bayesian optimization with Gaussian processes tunes four controller parameters using an expected improvement acquisition function. Optimization outcomes are validated against no device, zero torque, and general control baselines. Results: Optimization converges within an average of 142 s with a standard deviation of 24 s across all participants. The controller yields muscle activity reductions of 16.1% (p < 0.001) compared to no device, 21.7% (p < 0.001) versus zero torque, and 15.1% (p < 0.001) versus general control. EMG-based tuning is faster than metabolic-cost-based methods and perceived as less effortful, with Borg scale reductions of up to 39.5%. Conclusions: EMG-based HIL optimization significantly enhances controller tuning speed and effectiveness, demonstrating its potential for scalable and user-specific exoskeleton applications. Full article

Background/Objectives: Kinematic measurements obtained from functional tests have been used to identify associated and risk factors for the development of lower limb dysfunction, allowing targeted interventions to reduce potential risks and guide rehabilitation. It is necessary to identify variables and tests with adequate reliability and with the capability to discriminate individuals with and without lower limb functional deficits. This study aimed to determine which single-legged test (single-leg squat and single-leg landing) and variables (angle at deepest instant and range of motion) present the best reliability and capability to discriminate individuals with and without lower limb functional deficits. Methods: The frontal plane kinematics of 86 adults, divided into 2 groups (43 with lower limb functional deficits and 43 without), as classified by the Lower Extremity Functional Scale, were assessed during single-leg squat and single-leg landing tasks. The differences between groups in trunk, pelvis, hip, and knee ranges of motion and angles were tested using the independent T test or Mann–Whitney U test, and the test–retest, inter-rater, and intra-rater absolute (standard error of measurement and minimal detectable difference) and relative (intraclass correlation coefficient) reliability were calculated. Results: Trunk (r = 0.47), hip (r = 0.40), and knee (r = 0.35) angles at the deepest instant, as well as range of motion of the trunk (r = 0.33), pelvis (r = 0.47), and knee (r = 0.32) during the single-leg landing discriminated between groups (p < 0.05). For the single-leg squat, no variable discriminated the groups. Test–retest, inter-rater, and intra-rater reliability ranged from poor to excellent, with minimal detectable differences remaining below 19°. Conclusions: The single-leg landing and pelvis range of motion were the most effective tests and variables for discriminating individuals with and without lower limb functional deficits. Most variables demonstrated moderate test–retest and excellent inter-rater and intra-rater reliability. Full article

Background/Objectives: Postural control describes our ability to maintain an upright position. This study explored the impact of prolonged ankle plantar-flexed standing on postural control variability and strategy in an older adult population. The ability to perceive balance change was also assessed via subjective balance-related variables. Methods: Twenty-four community-dwelling older adults were recruited via convenience sampling. Each participant completed a balance confidence and falls efficacy questionnaire at baseline. Five barefoot quiet standing trials on a force plate then followed (Timepoint 1). After this, the participants stood with their ankles in a plantar-flexed position for up to 7.5 min before completing another quiet standing trial on the force plate. Four further ankle plantar-flexed standing trials of 2 min were then completed, interspersed with quiet standing trials on a force plate (Timepoint 2). The balance confidence and falls efficacy questionnaires were then completed again. For measures of postural control variability (sway path length, root mean square [RMS], sway area) and strategy (fractal dimension), mean values for the five trials were calculated for Timepoints 1 and 2 separately. Results: The sway path length and RMS measures were significantly increased (p < 0.05) at Timepoint 2. However, the fractal dimension did not change. There was also no change in balance confidence or falls efficacy. Conclusions: The findings suggest that prolonged standing can impact measures of postural variability without a change in postural control strategy. Postural control change also occurred without a change in subjective balance measures, suggesting that the altered balance may not be practically significant or perceptible to the individual. Full article