Biomechanics, Volume 6, Issue 1 (March 2026) – 31 articles

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. Full article

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 (RF_max, %), 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. RF_max 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. Full article

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. Full article

Background/Objectives: In pole vaulting, the capacity to store elastic energy within the pole (E_pole) significantly influences performance. This study investigated the characteristics of E_pole 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). E_pole 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 E_pole (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 E_pole. 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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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 $\dot{V}{O}_{2max}$) 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 $\dot{V}{O}_{2max}$ 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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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. Full article

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 (a_max) was measured via a horizontal linear position encoder (LPE; 1080 Sprint). Results: The shared variance between a_max 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. Full article

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. Full article

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. Full article