Stiff landing mechanics has been associated with increased anterior cruciate ligament (ACL) injury risk, yet it may optimise jump performance, creating a theoretical performance-injury conflict. This study examined movement patterns, their consistency, and performance during two-leg drop vertical jumps (DVJ) and single-leg drop vertical jumps (SDVJ). Forty-six healthy adults completed 3D motion analysis of DVJ from 30 cm and SDVJ from 15 cm, along with isokinetic knee torque testing. Ten ACL injury-related biomechanical variables were analysed using principal component analysis and hierarchical clustering. Clustering based on movement mechanics revealed three patterns: high-stiffness (shorter contact time, reduced joint flexion, greater joint moments and vertical GRF), medium-stiffness, and soft-stiffness (longer contact time, deeper flexion, lowest moments and GRF). Jump height did not differ between clusters, and 46% of participants changed pattern between tasks. Isokinetic knee extensor torque differed between the high- and soft-stiffness groups only in SDVJ, with greater values in the high-stiffness group. A separate performance-based classification (median split) revealed large differences in jump height-up to twofold-yet no difference in peak vertical GRF. These findings highlight the need for task-specific assessments that consider both discrete metrics and propulsive force production when identifying at-risk athletes while preserving performance potential.
Clinical guidelines recommend foot orthoses for patients with patellofemoral pain (PFP) and excessive subtalar pronation. Although Statistical Parametric Mapping (SPM) is established for analysing continuous kinematic waveforms in biomechanics, foot orthoses research in PFP frequently relies on discrete variables (e.g. peak angles). Applying SPM allows detailed assessment of movement adaptations throughout the stance phase that isolated data points may overlook. This study evaluated the immediate effects of medially wedged orthoses on lower limb kinematics, pain, and self-perceived improvement in runners with PFP. Thirty participants (15 men/15 women) ran under two conditions: original shoe insoles (control) and 4° medially wedged orthoses (intervention). Rearfoot, tibial, and femoral 3D kinematics were analysed using SPM. Compared with control, orthoses reduced rearfoot eversion (18-81% stance, p = 0.007), tibial internal rotation (40-84%, p < 0.001), and increased femoral adduction (23-47%, p = 0.011). Acute pain remained unchanged (p = 0.940), but more runners reported self-perceived improvement (p = 0.031). SPM identified time-specific alterations missed by discrete analyses. Medially wedged orthoses reduce distal rotations while increasing proximal adduction. Greater self-perceived improvement suggests short-term clinical benefits despite no immediate pain reduction. .
Surface-related alterations in joint loading during trail running remain unclear. Twenty male recreational rearfoot-strike runners performed overground running at 3.3 m/s on concrete and artificial turf. Three-dimensional kinematics, ground reaction forces (GRFs), and surface electromyography (sEMG) were recorded. An OpenSim Gait2392 model combined with Static Optimisation and Joint Reaction Analysis was used to estimate ankle, knee, and hip joint reaction forces (JRFs). Vertical and anteroposterior GRFs and vertical JRF peaks showed no significant differences between surfaces. However, the concrete surface yielded larger mediolateral GRF magnitudes (p < 0.001) and higher peak anterior ankle JRF (p = 0.049). Exploratory analyses indicated potential differences in knee and ankle mechanics, but these did not survive false discovery rate correction. Under speed-controlled running conditions, surface type had limited effects on vertical GRF and proximal joint loading. Adaptations to different surfaces appear to occur mainly through distal mechanical adjustments, particularly at the ankle and in mediolateral force control. .
Pirouette performance has been widely analysed biomechanically, with performance quantified by disparate measures. Therefore, this study examined the criterion validity of biomechanical measures in relation to expert ratings of balanced pirouette performance, and secondarily, dancers' subjective performance evaluations. Forty-nine dancers performed a collective 353 double pirouettes recorded with 3D motion capture. Dancers rated their own performance on a scale from 1 to 10. Following, kinematic data were used to create stick-figure videos, which three experts rated for balance performance on a scale of 1 to 6. Expert rating reliability was assessed with an Intraclass Correlation (ICC). Correlations were calculated between 16 kinematic measures and (1) expert observers' ratings of balance performance and (2) dancers' subjective ratings of overall performance. Overall, there was strong agreement among experts (ICC = 0.92). Dancer and expert ratings most strongly correlated with the pathlength of the supporting foot over the whole pirouette (rs-dancer = -0.59, rs-expert = -0.65). Interestingly, total degrees of trunk rotation-a common field measure-did not significantly relate to expert or dancer ratings. Rather, supporting foot displacement was the strongest field-based correlate (rs-dancer = -0.50, rs-expert = -0.50). These findings thus provide a basis for selecting kinematic measures that reflect practitioner evaluations and underlying biomechanical principles of pirouette performance.
Windsurfing pumping is a key manoeuvre in the Olympic iQFOiL class, yet its on-water biomechanics and coordination remain undescribed. This exploratory study quantified in situ kinematics and inter-element coordination during upwind pumping in seven elite windsurfers. A board-mounted camera recorded 36 race-pace upwind pumping sequences, and OpenPose-based markerless motion capture was used to estimate centre of mass (COM), knee and trunk angles, and COM-to-sail (CTS) and COM-to-board (CTB) distances. We conducted laboratory validation trials of the pumping motion to compare the markerless approach with a marker-based motion capture system. Field data showed large ranges of motion in the knee (58.8 ± 12.0°), trunk (37.1 ± 10.8°), CTS (16.1 ± 4.0 %H; % of body height) and CTB (10.9 ± 3.0 %H). Cross-correlation analysis revealed synchronous coordination between CTS, knee and trunk (lags < 5% of the cycle) and antiphase coordination between CTS and CTB. Together, these findings identify a whole-body pumping strategy in which knee and trunk motion are tightly coordinated to drive CTS and provide quantitative targets for coaching, simulator design and lab to field integration.
Trunk-arm coordination influences throwing-arm torques in baseball pitching, yet quantitative descriptions of coordinated trunk-arm motion are lacking. This study described trunk-arm coordination during pitching using joint excursion ratios and clarified the relationships between joint excursion ratios and biomechanical efficiency. 18 Division III college baseball pitchers underwent markerless motion capture, from which four joint excursion ratios and throwing-arm torques were calculated. Pearson coefficients described associations between joint excursion ratios and throwing-arm torques normalised by height, mass, and ball velocity. Multivariable linear regression models predicting raw throwing-arm torques and containing mass and each significantly correlated joint excursion ratios as predictors were compared to univariable models containing mass alone. Significant associations were observed between elbow extension/trunk rotation (EETR) ratio and normalised peak elbow (r = -0.47, p = 0.045) and peak shoulder (r = -0.51, p = 0.025) torques. Addition of EETR ratio explained 16% greater variance in raw shoulder external rotation torque/ball velocity and 13% greater variance in raw elbow valgus torque/ball velocity than mass alone. This study suggests EETR ratio during the first half of the acceleration phase is associated with biomechanical efficiency.
This randomised controlled trial investigated the effects of an 8-week anti-movement core training programme on phase-specific abdominal antagonist co-activation (CoA) and thorax-pelvis kinematics in amateur golfers. Participants were randomly allocated to an Experimental group (EXP, anti-movement core training), a traditional core training group (TCP), or a control group (CON). Training groups completed supervised sessions three times per week. Surface electromyography of the external oblique and 3D kinematics were recorded during the golf swing pre- and post-intervention. Results revealed that the EXP group demonstrated a unique phase-specific CoA modulation: significant preparatory increases during the takeaway and backswing, followed by rapid downregulation during the early downswing, which differed significantly from TCP (p < 0.05). While both EXP and TCP improved clubhead speed, only EXP significantly increased peak X-factor velocity and peak thorax rotational velocity (p < 0.05). Pelvic rotational velocity remained unchanged. Compared with traditional core training, anti-movement core training was associated with greater phase-specific modulation of external oblique co-activation and greater improvements in rotational kinematic variables. These findings suggest that incorporating multi-planar anti-movement core exercises may be a useful approach for improving trunk movement coordination and golf swing performance in amateur golfers.
Comparative data on markerless motion capture systems for upper-extremity kinematics during high-speed movements remain limited. We aimed to examine inter-system modelling differences in shoulder joint kinematics between a markerless motion capture system (Theia3D) and a marker-based system during baseball pitching, focusing on a wide range of shoulder joint motion throughout baseball pitching. Six collegiate pitchers completed 117 trials recorded simultaneously by both systems. Shoulder joint angles and joint centre positions were compared using nested Bland-Altman analysis, intraclass correlation coefficients (ICC (3,1)), and statistical parametric mapping (SPM). At maximum external rotation (MER), inter-system differences were small for external rotation (bias: -0.3°; ICC = 0.77), whereas the horizontal angle demonstrated a pronounced fixed bias (bias: -19.1°). At ball release (BR), inter-system differences increased across all joint angles, with the largest discrepancy for external rotation (bias: -8.5°; ICC = 0.33). Proportional bias was evident for most variables at BR. Between-participant variance exceeded within-participant variance at MER, indicating that participant-specific offsets were primary contributors to the limits of agreement. SPM identified significant inter-system differences during the acceleration phase. These findings highlight the importance of understanding the characteristics of each modelling approach for appropriate interpretation and application of markerless motion capture in overhead athletes.
This study investigated the acute effects of combat boots and minimalist shoes on Achilles tendon (AT) loading during running under different load carriage magnitudes in soldiers. Eighteen rearfoot-strike soldiers performed running tests under three load conditions (0, 10, and 20 kg) while wearing either minimalist shoes or combat boots. The coordinates of the body landmarks and ground reaction force data were simultaneously collected using the infrared high-speed motion capture system and force plates. The musculoskeletal model was established to calculate AT biomechanical parameters. Results showed that AT force impulse and stance duration increased with higher load magnitudes. Load carriage increased AT force during the midstance phase but decreased it during the early stance phase. Compared with combat boots, running in minimalist shoes decreased AT force during the terminal stance phase and shortened stance duration but increased AT force during the early stance phase. However, no main effect of footwear on AT force impulse was found. Additionally, no interaction effect between footwear and load carriage magnitude was observed for any biomechanical parameter. These findings suggest that minimalist shoes provide limited acute benefits in reducing cumulative AT loading and therefore are not recommended for soldiers during load carriage.
Sports biomechanics researchers and practitioners invest considerable effort in understanding the often complex interactions between athletes' techniques and their performance outcomes. Extensive research and commentary exist on the measurement of technique, including the wide range of technology available and the many diverse forms, structures and domains of the variables quantified. The analytical methods used to understand the interactions between these measures of technique and performance outcomes have also received considerable attention. However, the process of selecting the performance outcome measure rarely receives explicit focus, even though it can bias the conclusions reached for a variety of reasons. We therefore present a seven-step procedural framework to guide the selection or development of appropriate performance outcome measures for sports biomechanics investigations. Three published examples from our previous work, supported by other hypothetical scenarios, illustrate how the framework can be applied from different perspectives and across different sports. The framework will better enable biomechanists to identify, evaluate, and mitigate conceptual and measurement-related biases in established and novel performance measures. Ultimately, it supports the selection of outcome measures that best suit the given question, enhancing the validity and impact of biomechanical investigations designed to support sports performance.
This study investigated how different levels of sprint assistance influence neuromuscular activity and performance. Concerns exist that full assistance may reduce active muscle engagement due to passive contributions. Thirteen male athletes from various sports performed 30-m sprints under three conditions: unassisted, partially assisted, and fully assisted, using a motorised towing device. Surface electromyography recorded activity of five lower limb muscles (rectus femoris, vastus lateralis, semitendinosus, biceps femoris, and gluteus maximus), while spatiotemporal parameters were measured over the final 10 m using Optojump. Sprint times were significantly improved in both assisted conditions compared to unassisted sprints (partial: -3.4%, full: -2.8%; p < 0.01), primarily due to increased stride length (p < 0.001), longer flight time, and shorter contact time (p < 0.05 for both), while stride frequency remained unchanged. Contrary to hypothesis, EMG analyses revealed no statistically significant differences in muscle activity between conditions, despite improved performance and the potential contribution of passive propulsion. Large effect sizes (d > 0.8) were briefly observed, in a muscle-dependent manner, at discrete points of the gait cycle. These findings suggest that assisted sprinting enhances performance without reducing neuromuscular demands, although the results should be interpreted in light of the athletes' inexperience with assisted running.
The effects of arm position at lead foot contact (FC) on shoulder and elbow joint kinetics are not well understood. This study investigated the effects of wrist height relative to the shoulder at FC on the joint moments and pitching kinematics in high school and collegiate pitchers using a motion capture system. Peak elbow varus and shoulder internal rotation moments, along with upper extremity, pelvis, and upper torso kinematics, were compared among pitchers with the wrist positioned below, at, or above the shoulder at FC. Compared with pitchers whose wrist remained below the shoulder, those with the wrist above the shoulder demonstrated greater elbow varus and shoulder internal rotation moments, greater shoulder external rotation and upper torso rotation throughout most of the arm-cocking phase, a shorter arm-cocking phase, and earlier timing of key pitching events. Delaying the throwing arm motion during the stride by having a wrist below the shoulder at FC may help elongate the arm-cocking phase and minimize joint moments. Wrist height at lead foot contact may provide a simple and practical method for identifying pitchers who may be experiencing elevated joint loading. The findings also support the concept that pitching mechanics at lead foot contact influence kinematics throughout the subsequent phases of the pitching motion.
Advances in wearable technology have improved the ability to measure spatiotemporal gait parameters and training metrics in real-world environments, providing greater insight into how runners accumulate mechanical load. While spatiotemporal parameters such as velocity and cadence are associated with tibial acceleration (TA), these relationships have typically been examined at fixed velocities under controlled conditions, and do not consider their potential interaction or reflect real-world running conditions. The purpose of this study was to investigate the association between running velocity, cadence and TA in an outdoor environment. One hundred recreational runners ran on an athletics track at five velocities, ranging from very slow to very fast, based on their self-selected training pace. The results showed a significant interaction effect between cadence and velocity for both axial (p=0.002) and resultant TA (p<0.001). The estimated increase in axial TA for every 1-step increase in cadence ranged from 0.017 g to 0.042 g across the five velocity bands. For resultant TA, the estimated increase ranged from 0.006 g to 0.082 g. These findings suggest that cadence had a larger effect on TA at faster velocities, highlighting the importance of monitoring cadence in conjunction with velocity to inform TA.
Understanding the factors contributing to running-related injuries is important, since such injuries are common among runners. Vertical ground reaction forces (vGRFs) can help quantify biomechanical load during running, but are typically measured using force plates in laboratory settings. To allow continuous monitoring outdoors, wearable sensors such as inertial measurement units (IMUs) may offer a practical alternative. These sensors are often also embedded in smartwatches and heart rate monitor belts. This study aimed to predict vGRF using IMUs placed on the wrist and sternum-mimicking smartwatch and heart rate strap positions-combined with smartwatch-derived variables. Eleven rearfoot strike runners completed twelve 90-s treadmill trials at four speeds (8, 10, 12, 14 km/h) and three cadences (preferred ±10%). IMUs captured 3D acceleration and angular velocity; pressure insoles provided vGRF estimates used for outdoor validation. Subsequently, participants ran outdoors on an athletics track at the same four speeds. A long short-term memory (LSTM) neural network was trained to predict vGRF from IMU data. Feature importance analysis showed the sternum IMU contributed most to prediction accuracy. Leave-one-subject-out cross-validation, using all features, yielded an RMSE of 0.10 ± 0.024 body weight compared to indoor force plate measurements. Outdoor validation showed no significant performance drop. These results suggest that wearable devices enable meaningful vGRF monitoring during outdoor running.
Elbow injuries-particularly to the ulnar collateral ligament (UCL)-have been a problem in sports medicine for at least half a century. As a pitcher rotates his trunk to face the target and externally rotates his throwing arm, varus torque is produced at the elbow to decelerate arm cocking and initiate arm acceleration. With today's pitchers being larger, throwing harder, and playing more often during their development years, repetition of large varus torque leads to more UCL injuries. Pitch count limits for games, seasons, and per year may provide some prevention of overuse injuries. Varying efforts of pitching (instead of maximum effort on every pitch) may both reduce UCL damage and also improve performance (by throwing off the timing of hitters). Improving pitching biomechanics can lead to both increased pitch performance metrics (ball velocity, spin rate, and movement) and reduced elbow varus torque. The proliferation of baseball biomechanics in professional baseball, universities, and performance centres has amplified the potential of biomechanical intervention. In addition, a novel proposal is to modify the baseball itself; initial research shows reduced torque with slightly increased ball weight and circumference. In summary, baseball has an elbow injury problem; biomechanics may have the solution.
Tennis-serve landing is a high-intensity single-leg impact requiring coordinated multi-joint control, yet skill-level differences in whole-limb kinetics remain unclear. Fifteen elite and fifteen amateur male players performed Pinpoint serves. 3D kinematics and kinetics were captured. Principal component analysis (PCA) extracted synergy moments (Syn1-Syn2), and vector coding quantified coupling-angle coordination patterns. Two synergy moments explained the dominant variance. In Syn1, elites showed higher contributions from hip/ankle rotation (p = 0.032) and knee abduction-adduction (p < 0.001), whereas amateurs additionally over-weighted ankle plantar-dorsiflexion (p = 0.027). In Syn2, elites emphasised ankle plantar-dorsiflexion and inversion-eversion, hip abduction-adduction, and knee rotation (all p < 0.05 vs. mean); amateurs exceeded the mean only in hip abduction-adduction (p < 0.05) and knee rotation (p = 0.003). Elites showed greater Syn2 prevalence (p < 0.001) and higher proportions of Syn2-dominant anti-phase (p = 0.002) and in-phase patterns (p = 0.013); amateurs showed higher Syn1-dominant anti-phase patterns (p < 0.001). Elites dissipate rotational momentum through functional redundancy across joints, supporting robust stability. Amateurs rely on a stiffer, reactive braking strategy that may increase cumulative tissue loading. Training should develop multi-planar rotational adaptability to optimise landing mechanics and reduce injury risk.
This study used in-game markerless motion capture to develop a Super Learner ensemble model for predicting fastball velocity, with the aim of identifying key biomechanical contributors and evaluating generalisability across conferences. Data were collected from 322 NCAA Division I pitchers (ACC: n = 122; SEC: n = 200) between 2022 and 2024. The ensemble combined five algorithms-elastic net, random forest, support vector machines, gradient boosting, and multivariate adaptive regression splines (MARS)-and was trained using 10-fold cross-validation with internal-external validation by conference. Internal performance yielded RMSE 2.70 mph (95% CI 2.44-2.99), MAE 2.10 mph (95% CI 1.93-2.29), R2 = 0.29 (95% CI 0.21-0.36), and calibration slope = 0.99 (95% CI 0.83-1.15). Internal-external performance was direction-dependent (SEC→ACC RMSE = 3.04 mph, 95% CI 2.51-3.63; ACC→SEC RMSE = 2.55 mph, 95% CI 2.33-2.77). Height was the most influential predictor (81.2%), followed by mass (2.47%). Algorithm weights favoured elastic net (62.6%), followed by support vector machines (19.8%), gradient boosting (13.6%), and random forest (4%). Findings suggest that biomechanical strategies for generating velocity vary between groups and highlight the potential of ensemble machine learning to identify biomechanical contributors to fastball velocity and inform individualised analysis in baseball.
Running on unpaved trails is commonly perceived to reduce impact loading and injury risk, yet biomechanical evidence remains limited across age groups. We investigated the effects of paved versus unpaved surfaces on running biomechanics and surface-related injury risk perceptions in Master and young adult runners. Sixty participants (30 Master, 30 young adult) completed 5 km runs on both surfaces while wearing triaxial tibial accelerometers. We compared average cadence, peak resultant and axial tibial acceleration (TA), and cumulative resultant and axial TA using ANCOVA, controlling for running speed. Peak resultant TA was higher on unpaved than paved surfaces (p = .014), whereas cadence, peak axial TA, and cumulative axial and resultant TA did not differ between surfaces (p > .05). Master runners exhibited higher cadence and lower peak resultant TA than young adults (p < .05), while cumulative resultant TA did not differ by age (p > .05). Nearly half the participants (48.3%) perceived that running on unpaved trails reduces injury risk. Overall, unpaved trails produced higher peak TA without changing cumulative TA. Age-group differences in cadence were accompanied by lower peak resultant TA for Master runners, suggesting an age-related shift towards reduced per-step impact magnitude.
The movement and positioning of the body during the early phases of the pitching motion can have cascading effects on downstream mechanics. While stride mechanics have been the focus of recent research, the role of stance foot mechanics in generating ground reaction force (GRF) and influencing stride kinematics remains unclear. This study aimed to determine whether stance foot centre of pressure (COP) location and heel lift timing are related to stride-phase GRF and stride kinematics in baseball pitchers. Biomechanical data were collected from 60 high school and 15 collegiate pitchers using a motion capture system and force platforms. Within the high school pitchers, COP location at the time of peak forward GRF and heel lift timing were analysed in relation to GRF and stride mechanics. Most high school and collegiate pitchers generated peak forward force through the forefoot and maintained heel contact with the ground throughout most (~85%) of the stride phase of pitching. The timing of heel lift and COP location at the time of peak forward GRF were not associated with forward propulsive force, stride mechanics, or ball speed, but were associated with pelvis orientation at lead foot contact in high-school pitchers.
Running assessments are frequently conducted without inducing fatigability because achieving true exhaustion in athletes can be both time consuming and physically demanding. Blood flow restriction (BFR) presents a potential solution by reducing time-to-exhaustion. To determine whether running with BFR (1) accelerates fatiguability compared to standard running and (2) influences running spatiotemporal parameters, including step frequency, step length, contact time, flight time, and duty factor. Sixteen participants (11 men, 5 women) completed two cross-over running trials until exhaustion under two conditions: control and 80% occlusion BFR. Time-to-exhaustion and heart rate were recorded as well as pre/post run maximal voluntary isometric contractions for knee flexors, knee extensors, and ankle plantar flexors. Running spatiotemporal parameters were measured at 65% of maximal aerobic speed both before and after exhaustive running. The BFR protocol significantly shortened time-to-exhaustion (7 min 51 s ±2 min 54 s vs. 24 min 02 s ±12 min 10 s in control, p < .001). Heart rate at exhaustion was lower in the BFR condition (169.5 ± 19.0 vs. 188.1 ± 8.9 bpm, p = .001). Post-run knee flexors strength declined similarly in both protocols (~21%), indicating comparable neuromuscular fatigability despite the shorter BFR running time. None of the spatiotemporal parameters differed significantly between conditions (p > .074). Running with BFR accelerates fatigability without significantly affecting running spatiotemporal parameters.
