Search Results (146)

Forestry, nursery, and planting tasks involve repetitive trunk flexion, squatting, and kneeling, as well as manual handling, increasing musculoskeletal load, and the need for mobility-related safety measures. Passive exoskeletons could mitigate postural exposure and reduce the overall body workload. We conducted a preliminary study (n = 14) to test the feasibility of a protocol and estimated model- and task-specific trends during standardized simulated nursery activities in a laboratory setting. Participants simulated planting and seeding tasks (loads of 0.5–2 kg) and material handling and preparation tasks (loads of 5–15 kg) without an exoskeleton (No-EXO) and with three passive models (EXO 1–EXO 3). EXO 3 was excluded from the planting tasks for feasibility reasons. Whole-body kinematics were recorded using an IMU-based motion capture system and converted into time-based ergonomic exposure outcomes (OWAS and RULA). Physiological load was monitored via heart-rate (HR) measurements. Compared to the No-EXO condition, exoskeleton use shifted posture exposure towards lower-risk categories. The largest improvements were observed with EXO 2 and EXO 3 during material handling (OWAS: −18%/−20%; RULA action-level reduction: −25%/−39%) and with EXO 2 during planting/seeding (OWAS: −15%; RULA: −26%). HR_max did not increase across tasks or conditions and HR tended not to rise with higher workload when exoskeletons were used. Overall, the results suggest positive ergonomic and workload trends related to the model and tasks. Field validation on uneven terrain with full personal protective equipment and harness integration is needed to confirm usability and support and to define implementation requirements (fit, compatibility with PPE, and safe-use conditions). 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

This paper presents a data-driven modeling and sensorless angle–torque prediction method for a pneumatic soft bending actuator. The actuator contains no embedded angle or torque sensors; instead, only airflow and pressure sensors located in the external control box (standard components in pneumatic systems) are used during operation. The proposed method, and therefore eliminates the need for onboard sensing and detailed valve hysteresis modeling. Based on the ideal gas law, four continuous, monotonic, and single-valued pneumatic state equations were derived and experimentally validated. As a case study, a pneumatic soft actuator was designed to generate high torque for assisting knee and ankle extension. An experimental setup with multiple sensors collected key data on air mass, internal pressure, actuator torque, and bending angle. These additional sensors were used only during dataset generation. A data-driven modeling approach was developed with training neural networks to generate four fitting functions to predict actuator behavior, including equations for angle and torque prediction. An angle-sensorless closed-loop control simulation study, incorporating a PID controller, a proportional valve delay block, and torque prediction, demonstrated the controllability and computational feasibility of the proposed model as well as the actuator’s effectiveness in supporting additional weight during squat-to-stand motion. Full article

Muscular strength plays a crucial role in sports performance and is often evaluated using vertical jump tests such as the Squat Jump (SJ) and Countermovement Jump (CMJ). Measurements based on flight time (FT) assume that takeoff and landing postures are identical, yet differences in ankle position can introduce systematic errors. This study examined whether dorsiflexion (DF) or plantarflexion (PF) of the ankle during the flight phase affects jump height. Forty-three active university students completed four repetitions each of SJ and CMJ under DF and PF across two sessions. Jump heights were recorded using a Chronojump-Boscosystem platform. No significant difference was observed in SJ between DF and PF, while CMJ heights were consistently higher under DF (DF: 28.29 cm ± 7.7 cm vs. PF: 27.08 cm ± 7.03 cm, p = 0.001; d = 0.16). Notably, the effect of DF appeared more pronounced in CMJ, suggesting that higher jumps are more sensitive to postural variations. These findings could suggest that DF can artificially increase jump heights as measured on a jump platform, without reflecting true improvements in force production. Coaches and practitioners should interpret FT-derived data with caution, particularly for higher jumps. Future research combining precise motion capture with force platforms could directly track center-of-mass changes and validate this mechanism. Full article

Background: The integration of markerless motion capture systems such as OpenCap with force platforms expands the possibilities of biomechanical analysis in low-cost environments; however, it requires robust temporal synchronization procedures in the absence of shared hardware triggers. Objective: To develop and validate an automatic synchronization algorithm based on heel kinematic events to align OpenCap data with force platform signals during lower-limb functional exercises. Methods: Thirty normal-weight adult women (18–45 years) were evaluated while performing between 11 and 14 functional tasks (60° and 90° squats, lunges, sliding variations, and step exercises), yielding 330 motion records. Kinematics were estimated using OpenCap (four iPhone 12 cameras at 60 Hz), and kinetics were recorded using BTS P6000 force platforms synchronized with an OptiTrack system (Gold Standard). The algorithm detected heel contact from the filtered vertical coordinate and aligned this event with the initial rise in vertical ground reaction force. Validation against the Gold Standard was performed in 20 squat repetitions (10 at 60° and 10 at 90°) using Pearson correlation, RMSE, and MAE of the time-normalized and amplitude-normalized (0–1) vertical ground reaction force (vGRF). Results: The algorithm successfully synchronized 92.5% of the 330 records; the remaining cases showed kinematic noise or additional steps that prevented robust event detection. During validation, correlations were r = 0.85 (60°) and r = 0.81 (90°), with Root Mean Square Error (RMSE) < 0.17 and Mean Absolute Error (MAE) < 0.14, values representing less than 0.1% of the peak force. Conclusions: The heel-contact-based algorithm allows accurate synchronization of OpenCap and force platform signals during lower-limb functional exercises, achieving performance comparable to hardware-synchronized systems. This approach facilitates the integration of markerless motion capture in clinical, sports, and occupational settings where advanced dynamic analysis is required with limited infrastructure. Full article

This systematic review focused on the validity of markerless motion capture (MMC) systems used for human movement assessment during tasks that involve physical interaction with objects. Five electronic databases were searched until May 2025. Eligible studies (i) assessed the validity of an MMC system, (ii) required human participants to perform tasks that involved physical interaction with objects (e.g., lifts, carrying, gait with loads), (iii) employed a marker-based reference system, and (iv) reported at least one kinematic metric. Risk of bias was assessed using the SURE checklist. A best-evidence synthesis was conducted to classify the level of evidence across included studies. Fifteen studies met eligibility (median = 21 participants per study). In general, MMC systems presented good performance in capturing the waveforms related to movement (i.e., high associations with reference systems), but its level of precision (i.e., the magnitude of differences to the reference systems) still requires improvement regarding tasks involving human–object interactions. Most tasks analyzed were lifts, gait with load, squatting and reaching/manipulation, and technical gestures. There was strong evidence for the validity of MMC for implementation during lifting tasks. In summary, markerless motion capture (MMC) systems exhibit promising evidence of validity for some human–object interaction tasks, that is, especially when lifting as strong evidence was observed across studies on this type of task. In contrast, some evidence for tasks including gait under load, squatting, reaching, or touchscreen interaction is limited, moderate, or conflicting. Notwithstanding these limitations, most studies were observed to have moderate- to high-quality methodology. Additional research is required to optimize protocols to study the measurement error aspects of MMC under human–object interaction in real-world environments. Full article

In agricultural workplaces, upper-body strain arises not only from lifting and carrying harvest crates but also from pushing, pulling, twisting, and squatting motions. Drawing inspiration from the momentary shoulder contraction and whole-body coordination characteristic of traditional Japanese martial arts, this study proposes a method for “moving efficiently with minimal exertion” across multiple task actions, specifically, lateral pushing, fore-aft pulling, and trunk rotation. Each action is modeled as a control system, and mechanical-engineering simulations are employed to derive optimal muscle-output patterns. Simulation results indicate that peak muscular force can be lowered compared with conventional techniques. A simple physical test rig confirms the load-reduction effect, showing decreases in both perceived exertion and electromyographic activity. These findings offer practical knowledge that can be immediately applied not only to agriculture but also to logistics, nursing care, and other settings involving repetitive handling of heavy objects or machine operations. Full article

This study investigates the joint mechanical power (JMP) distribution in the half squat (HS) exercise through the Power-Based Training (PBT) framework, with the primary aim of providing preliminary methodological validation of this analytical approach and illustrating its capacity to characterize joint contributions across movement phases and load levels. Five professional weightlifters performed HS under five progressive loads (20–80% 1RM), while kinematics and kinetics were recorded with a Vicon motion capture system and force platforms. JMP at the hip, knee, and ankle was analyzed in four distinct movement phases. Results indicated that joint contributions varied with load and phase. Under light loads the knee tended to produce most power. As load increased, contributions shifted proximally: the hip increased both absorption and production, and the ankle’s relative contribution grew in the final lifting phase. The main eccentric (lowering deceleration) and concentric (lifting acceleration) phases concentrated the highest JMP values, though differences between phases diminished at higher loads, suggesting a more homogeneous effort distribution. These findings support the feasibility of the PBT framework for methodological joint-level analysis. Given the pilot scope and purposive elite sample, results are not intended for population inference but inform about methodological applications in training, rehabilitation, and injury-risk assessment. Full article

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

A biomechanical evaluation of knee loading during squatting is essential for understanding functional capacity after total knee arthroplasty (TKA). This study compares knee joint kinetics in healthy native knees and in posterior-stabilized TKA (PS-TKA) across BMI categories using 3D motion capture and inverse dynamics. Sixty-two knees (31 healthy, 31 PS-TKA) were analyzed. Native knees demonstrated greater flexion capacity and higher joint loading than PS-TKA knees. Peak resultant joint forces reached 3.50 ± 1.00 BW in healthy knees compared with 2.90 ± 1.20 BW in PS-TKA knees. Healthy knees also generated higher joint moments, with maximum adduction and rotation moments of 5.07% BW × height and 1.29% BW × height, respectively. Body mass index (BMI) significantly influenced loading patterns in native knees, increasing anterior–posterior forces, quadriceps demand, and resultant moments, whereas loading in PS-TKA knees showed minimal BMI dependence. These findings highlight fundamental biomechanical differences between native and prosthetic knees and provide population-specific insights relevant to rehabilitation and high-flexion activities common in Asian populations. Full article

This study aimed to compare the acute effects of three eccentric training strategies—constant resistance (CR), accentuated eccentric loading (AEL), and accelerated eccentrics (AE)—on the performance and biomechanical characteristics of the concentric phase of the squat, while maintaining a consistent squat depth. Twenty-four experienced resistance-trained male collegiate athletes (age: 21.92 ± 2.66 years; height: 175.88 ± 4.39 cm; body mass: 73.18 ± 8.08 kg) were recruited. A randomized crossover design was employed, where participants completed three squat protocols (eccentric load/concentric load/eccentric duration): AEL (90% 1RM/60% 1RM/2 s), CR (60% 1RM/60% 1RM/2 s), and AE (60% 1RM/60% 1RM/as fast as possible). Throughout the squats, kinematic and kinetic data were synchronously collected using an 8-camera 3D infrared motion capture system and two 3D force plates. The mean concentric barbell velocity in the AE condition was significantly higher than in both the AEL and CR conditions (p < 0.001). Furthermore, the AE condition demonstrated significant advantages in multiple biomechanical variables, including peak ground reaction force, as well as peak angular velocity and peak joint moments of the three lower limb joints (p < 0.05). With identical concentric loads and range of motion, increasing the velocity of the eccentric phase significantly enhances subsequent concentric performance and force output. In contrast, while the AEL strategy increases the mechanical load during the eccentric phase, its potentiating effect on concentric performance is relatively limited. These findings suggest that eccentric velocity may be a more critical variable than eccentric load in strength training. Full article

Background: Posterior pelvic tilt during the squat, commonly referred to as “butt wink” can potentially increase the risk of spine injury when squatting this way. The main goal of this study is to objectively assess the immediate effect of a short-term exercise intervention on the total pelvis range of motion in the sagittal plane (mainly posterior pelvic tilt). Methods: This study has a quasi-experimental design with the participants divided into experimental and control groups based on pre-existing condition—occurrence of PTT during bodyweight squat. A total of 42 participants (21 females and 21 males) were divided into an experimental group (n = 23) and a control group (n = 19). The division was made according to the incidence of posterior pelvic tilt during the bodyweight squat. Qualisys, three-dimensional kinematic motion analysis with Functional Assessment module, was used to analyze pelvis kinematics. Both groups underwent a twenty-minute exercise intervention aimed at strengthening trunk stabilizing muscles, improving squat technique and body awareness in space. Data from the three-dimensional kinematic motion analysis were statistically processed using Restricted Maximum Likelihood analysis (REML) of linear mixed models and repeated measures analysis of variance (rANOVA); Results: There was no statistically significant difference in the range of motion of posterior pelvic tilt before and after the exercise intervention (p = 0.89 and p = 0.42). Only the individual repetitions of the squat were statistically significantly different from each other (p < 0.001) and no statistically significant relationship between posterior pelvic tilt and initial pelvic position was found (p = 0.13). Conclusions: The short exercise intervention did not acutely alter pelvic kinematics (the range of motion of posterior pelvic tilt). Future research should focus on longer exercise interventions (4–8 weeks) with progressive loading and looking for possible associations between different variables of squat execution and the incidence of posterior pelvic tilt. Full article

People with Parkinson’s disease (PD) experience mobility impairments that impact daily functioning, yet conventional clinical assessments provide limited insight into real-world mobility. This study evaluated motor-state classification and the concurrent validity of mobility metrics derived from augmented-reality (AR) glasses against a markerless motion capture system (Theia3D) during gamified AR exercises. Fifteen participants with PD completed five gamified AR exercises measured with both systems. Motor-state segments included straight walking, turning, squatting, and sit-to-stand/stand-to-sit transfers, from which the following mobility metrics were derived: step length, gait speed, cadence, transfer and squat durations, squat depth, turn duration, and peak turn angular velocity. We found excellent between-systems consistency for head position (X, Y, Z) and yaw-angle time series (ICC_(c,1) > 0.932). The AR-based motor-state classification showed high accuracy, with F1-scores of 0.947–1.000. Absolute agreement with Theia3D was excellent for all mobility metrics (ICC_(A,1) > 0.904), except for cadence during straight walking and peak angular velocity during turns, which were good and moderate (ICC_(A,1) = 0.890, ICC_(A,1) = 0.477, respectively). These results indicate that motor states and associated mobility metrics can be accurately derived during gamified AR exercises, verified in a controlled laboratory environment in people with mild to moderate PD, a necessary first step towards unobtrusive derivation of mobility metrics during in-clinic and at-home AR neurorehabilitation exercise programs. Full article

Background: The aim was to compare the effects of full squat (FST) versus half squat training (HST) on body composition, muscle hypertrophy, and mean propulsive velocity (MPV) in young athletes. Methods: Twenty-eight highly trained male tennis players (13.88 ± 0.91 years, 166.08 ± 11.30 cm, 57.40 ± 8.99 kg, 14.34 ± 2.75% body fat) were randomly allocated to an eight-week FST or HST program. Training volume load was matched between interventions, and the only difference was the range of motion (squat depth). Pre- and post-training tests evaluated body composition (body mass and body fat percent), muscle hypertrophy (muscle volume of the thigh, calf, and leg, and cross-sectional area at half and maximum circumference of the thigh), and MPV at 45 and 50% of one-repetition maximum (1RM). An analysis of variance was used to analyze differences. Results: The results exhibited significant group-by-time interactions for body mass (p = 0.002, ηp² = 0.32), body fat (p < 0.001, ηp² = 0.71), and MPV (all p ≤ 0.005, ηp² ≥ 0.27). Post hoc comparisons showed that both groups presented significant improvements in body composition, muscle hypertrophy, and MPV (all p ≤ 0.004). However, FST outperformed HST in body fat (p = 0.032) and MPV at both %1RM (p < 0.001). Conclusions: Overall, FST would be preferred over HST for tennis training in youth athletes. Four to five sets of 8–12 repetitions at 60–70% 1RM, two days a week during preseason, appear to be sufficient to induce neuromuscular performance improvement and enhance body composition. Full article

Optimal lower limb biomechanics are crucial for movement efficiency and injury prevention in football players. The single-leg squat serves as a valuable assessment tool for neuromuscular control, providing insight into movement patterns and potential imbalances. Deficits in hip strength, ankle mobility, and foot alignment can significantly influence biomechanics, leading to compensatory movements and increased joint stress. Identifying and addressing these factors through targeted training can enhance performance and reduce the risk of injury. This study aimed to examine the relationship between hip and ankle/foot mobility, strength, and alignment with hip kinematics during the single-leg squat in football players. A cross-sectional study assessed 25 professional football players. Measurements included isometric strength of the hip abductors and external rotators, ankle dorsiflexion range of motion, and shank–forefoot alignment. Hip kinematics during the single-leg squat were analyzed using Inertial Measurement Units, and Pearson’s correlation coefficient was applied (p < 0.05). Shank–forefoot alignment showed moderate to strong correlations with contralateral pelvic drop (r = 0.44; p = 0.035), hip adduction (r = 0.42; p = 0.036), and hip internal rotation (r = 0.51; p = 0.009) during the single-leg squat. These findings highlight the importance of foot alignment in movement control, reinforcing its relevance for injury prevention strategies in football players. Full article