Search Results (93)

Deploying unmanned aerial vehicles (UAVs) cooperatively with legged robots for disaster response and inspection requires autonomous docking on miniature walking platforms. This study addresses the problem of landing a foldable quadrotor onto the back of a trotting wheel-legged robot ($300\times 180$ mm) and subsequently taking off while carrying it as a payload. Four tightly coupled challenges distinguish this task from conventional mobile-platform landing: (i) an extremely small landing surface, (ii) gait-induced periodic vibrations at $2.5$ Hz, (iii) continuous platform translation at $0.3$–$0.8$ m/s, and (iv) surface docking that requires simultaneous position and attitude matching rather than mere point tracking. The proposed framework comprises four components: (1) a novel single-servo crank-rocker folding mechanism that reduces the folded body footprint by 48.5% and the maximum linear dimension from 590 mm to 309 mm (↓47.6%) compared with the prior dual-servo design; (2) a staged Continuous Fast Nonsingular Terminal Sliding Mode (CFNTSM) controller combined with a Gait-Frequency-Aware Finite-time Extended Observer (GFA-FEO); (3) a Feature-wise Linear Modulation Soft Actor-Critic (FiLM-SAC) residual reinforcement-learning policy conditioned on physical states and mission phase, with an adaptive trust weight $\lambda \left(t\right)$; and (4) a payload-adaptive takeoff strategy with parameter hot-switching to handle the twofold mass increase. Extensive Monte Carlo simulations and ablation studies across three experiment groups demonstrate that the proposed hierarchical framework achieves sub-centimetre (<10 mm) position accuracy and <3° attitude matching on a walking platform. Quantitatively, the full method reduces docking RMSE by 42% relative to the model-based CFNTSM + GFA-FEO controller without residual RL (4.2 vs. 7.2 mm) and reduces post-lock takeoff RMSE by 63% through FEO hot-switching (16.2 vs. 44.2 mm). Full article

This study evaluated the test–retest reliability, standard error of measurement (SEM), and minimal detectable change (MDC) of frontal plane projection angles (FPPAs) across five single-leg tasks in individuals with patellofemoral pain (PFP). Two-dimensional video data was collected from ten individuals with predominantly unilateral PFP. Participants performed single-leg squat, single-leg landing, single-leg hop, forward step-down, and lateral step-down across two testing sessions. FPPAs were measured at peak knee flexion for each task, including trunk lean angle, knee FPPA, hip FPPA, and dynamic valgus index. Test–retest reliability was assessed using intraclass correlation coefficients (ICCs). Our findings indicate that test–retest reliability and measurement error for trunk and lower limb FPPA varied across tasks in individuals with PFP. The lowest ICC was observed for hip FPPA, particularly during single-leg squat and lateral step-down tasks. Among the five tasks tested, the single-leg squat appeared to be the most demanding task, demonstrating the lowest ICCs, and highest SEM and MDC values across all four outcome measures (trunk lean angle, knee and hip FPPAs, and dynamic valgus index). The dynamic valgus index consistently showed larger SEM and MDC values than isolated hip or knee FPPAs, likely reflecting compounded measurement errors across segments. These findings provide preliminary insights, though confirmation in larger samples in persons with PFP is warranted. Full article

Pre-elite female field hockey players have a high incidence of lower extremity injury, highlighting the need for practical and reliable screening approaches. A dual assessment combining Functional Performance Tests (FPTs) with movement quality scoring (QASLS) may provide a more comprehensive evaluation; however, its reliability in this population is unclear. Fifteen pre-elite female field hockey players (16.7 ± 0.7 years) completed an FPT battery (anterior reach (AR), single leg drop vertical jump–land (DVJL), single hop for distance (SHFD), side hop (SH)) on two occasions, 28 days apart. Movement quality was assessed by three raters using QASLS. Reliability was evaluated using ICC with 95% confidence intervals (CI), alongside standard error of measurement (SEM), smallest detectable difference (SDD), and percentage exact agreement (PEA). Test–retest reliability varied across tasks (ICC_2,1 0.33–0.90), with wide confidence intervals indicating uncertainty in several estimates. AR demonstrated the most consistent reliability, supporting its use for monitoring over time. In contrast, the DVJL and SH showed the greatest variability, likely reflecting higher task complexity, while the SHFD required relatively large performance changes to exceed measurement error. Intra-rater reliability for QASLS was consistent across the FPT battery (ICC_2,k 0.79–0.90), whereas inter-rater reliability was more variable (0.38–0.82), indicating rater-dependent differences. PEA demonstrated generally high agreement (60–100%), although lower agreement was observed for pelvic alignment components. These findings support the use of a dual assessment approach as a practicable profiling approach in pre-elite female field hockey, enabling practitioners to identify movement deficits not captured by performance metrics alone. However, variability in complex tasks and between raters highlights the need to consider measurement error and implement standardised rater training when profiling or monitoring performance. Full article

Non-contact anterior cruciate ligament (ACL) injuries cause substantial time loss in female football. Although altered lower-limb muscle excitation is a modifiable risk factor, the reliability of surface electromyography (sEMG) during dynamic tasks in female players remains uncertain. This repeated-measures reliability study examined sEMG during a single-leg jump landing (LAND) and 90° sidestep cut (CUT) in 16 second-tier English female footballers. We evaluated reliability across: (1) within- versus between-session measures; (2) mean versus peak amplitudes; (3) pre-initial contact (PRE-IC) versus post-initial contact (POST-IC) phases; and (4) 10 ms versus 50 ms smoothing windows. Reliability was quantified using intraclass correlation coefficient (ICC[2,k]) and absolute measurement error. Within-session ICCs were moderate to excellent (LAND 0.61 to 0.95; CUT 0.68 to 0.96), whereas between-session ICCs varied from poor to excellent (LAND −0.48 to 0.94; CUT −0.08 to 0.93). Mean amplitudes showed marginally higher ICCs and lower absolute error than peaks. Phase-specific patterns were task-dependent: PRE-IC was more reliable in LAND, whereas POST-IC was more reliable in CUT. Practitioners should prioritize within-session comparisons using mean amplitudes, and the most reliable task-specific phase is recommended. Between-day application warrants caution, as the consistently lower reliability demonstrated may reflect task variability and/or physiological fluctuations rather than the sEMG method alone. 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: Improper landing mechanics in Taekwondo can lead to non-contact injuries such as ankle sprains and knee ligament tears, highlighting the necessity for objective methods to evaluate landing stability and injury risk. Electromyography (EMG) enables the examination of muscle activation patterns; however, conventional analyses based on simple averages have limited predictive value. Methods: This study analyzed EMG signals recorded during single-leg landings (45 cm height) in 30 elite male Taekwondo athletes. Participants were divided into regular exercise groups (REG, n = 15) and non-exercise groups (NEG, n = 15). Signals were segmented into two phases. Eight features were extracted per muscle per phase. Classification models (Random Forest, XGBoost, Logistic Regression, Voting Classifier) were used to classify between groups, while regression models (Ridge, Random Forest, XGBoost) predicted continuous muscle activation changes as injury risk indicators. Results: The Random Forest Classifier achieved an accuracy of 0.8365 and an F1-score of 0.8547. For regression, Ridge Regression indicated high performance (R² = 0.9974, MAE = 0.2620, RMSE = 0.4284, 5-fold CV MAE: 0.2459 ± 0.0270), demonstrating strong linear correlations between EMG features and outcomes. Conclusions: The AI-enabled EMG analysis can be used as an objective measure of the study of the individual landing stability and risk of injury in Taekwondo athletes, but its clinical application has to be validated in the future by biomechanical injury indicators and prospective cohort studies. Full article

Background: Neuromuscular electrical stimulation (NMES) is an effective exogenous neuromuscular activation method widely used in sports training and rehabilitation. However, existing research primarily focuses on land-based sports or single-joint movements, with limited in-depth exploration of its intervention effects and underlying neuromuscular control mechanisms for complex, multi-joint coordinated aquatic activities like breaststroke swimming. This study aimed to investigate the effects of NMES combined with traditional resistance training on neuromuscular function during sport-specific technical movements in breaststroke athletes. Methods: A randomized controlled trial was conducted with 30 national-level or above breaststroke athletes assigned to either an experimental group (NMES combined with traditional squat resistance training) or a control group (traditional squat resistance training only) for an 8-week intervention. A specialized fully waterproof wireless electromyography (EMG) sensor system (Mini Wave Infinity Waterproof) was used to synchronously collect surface EMG signals from 10 lower limb and trunk muscles during actual swimming, combined with high-speed video for movement phase segmentation. Changes in lower limb explosive power were assessed using a force plate. Non-negative matrix factorization (NMF) muscle synergy analysis was employed to compare changes in muscle activation levels (iEMG, RMS) and synergy patterns (spatial structure, temporal activation coefficients) across different phases of the breaststroke kick before and after the intervention. Results: Compared to the control group, the experimental group demonstrated significantly greater improvements in single-leg jump height (Δ = 0.06 m vs. 0.03 m) and double-leg jump height (Δ = 0.07 m vs. 0.03 m). Time-domain EMG analysis revealed that the experimental group showed more significant increases in iEMG values for the adductor longus, adductor magnus, and gastrocnemius lateralis during the leg-retraction and leg-flipping phases (p < 0.05). During the pedal-clamp phase, the experimental group exhibited significantly reduced activation of the tibialis anterior alongside enhanced activation of the gastrocnemius. Muscle synergy analysis indicated that post-intervention, the experimental group showed a significant increase in the weighting of the vastus medialis and biceps femoris within synergy module 4 (SYN4, related to propulsion and posture) (p < 0.05), a significant increase in rectus abdominis weighting within synergy module 3 (SYN3, p = 0.033), and a significant shortening of the activation duration of synergy module 2 (SYN2, p = 0.007). Conclusions: NMES combined with traditional resistance training significantly enhances land-based explosive power in breaststroke athletes and specifically optimizes neuromuscular control strategies during the underwater breaststroke kick. This optimization is characterized by improved activation efficiency of key muscle groups, more economical coordination of antagonist muscles, and adaptive remodeling of inter-muscle synergy patterns in specific movement phases. This study provides novel evidence supporting the application of NMES in swimming-specific strength training, spanning from macroscopic performance to microscopic neural control. Full article

Background: Patients after anterior cruciate ligament reconstruction (ACLR) often exhibit persistent biomechanical deficits, particularly during high-demand tasks like the single-leg drop jump (SLDJ). At approximately six months post-ACLR, patients frequently rely on visual input to compensate for persistent sensorimotor deficits during dynamic tasks, which may lead to altered movement patterns. While visual perturbations have been studied in bilateral jump tasks, their impact on SLDJ biomechanics in ACLR patients remains unexplored. Methods: Patients who were still engaged in rehabilitation and not yet cleared for unrestricted return to sport performed SLDJ under three visual conditions: normal vision, low visual perturbation, and high visual perturbation using stroboscopic glasses. Kinematic and kinetic variables were measured using a 3-dimensional motion analysis system and force platform. Comparisons were made between the ACLR and non-operated limbs, as well as across visual conditions. Results: 24 patients (17 males, 7 females; mean age 25.6 ± 6.3 years, mean height 174 ± 9.0 cm, mean weight 74.7 ± 17.2 kg) were included in the analysis. Knee adduction excursion during landing was significantly affected by visual perturbation (F(2, 46) = 6.55, p = 0.004, η² = 0.019). Post hoc analysis showed that high visual perturbation significantly decreased knee adduction excursion compared to normal vision on the ACLR limb (mean difference 1.499°, SE = 0.388, pBonf = 0.003, Cohen’s d = 0.542). A significant difference was also found between low and high visual perturbation on the ACLR limb (mean difference 1.543°, SE = 0.388, pBonf = 0.002, Cohen’s d = 0.558). No significant changes were observed in the non-operated limb across visual conditions. Conclusions: High visual perturbation significantly altered knee adduction excursion on the ACLR limb, resulting in a shift toward greater knee abduction during landing. No changes were observed in the non-operated limb. These findings support the use of visual perturbation in functional assessment protocols after ACLR to better identify persistent biomechanical deficits that may contribute to reinjury risk. Full article

Maintaining lower-limb joint stability is essential for safe and efficient performance during landing and directional changes. This pilot study examined the effects of a 10-week perturbation-based Dynamic Stability Training (DST) program using an inertial water load on lower-limb joint moments during single-leg landing and a 3-s stabilization phase following a 90° cutting maneuver. Fifteen healthy young men completed DST twice weekly. Three-dimensional motion capture and force-plate data were collected at pre-, mid-, and post-training to compute hip, knee, and ankle joint moments. During landing, hip flexion and abduction moments increased, whereas knee abduction moment decreased. During the stabilization phase, hip flexion, hip rotation, and ankle abduction moments decreased, while knee abduction moment increased. These joint-specific changes suggest potential adaptations in frontal- and transverse-plane control when training with unstable inertial water loads; however, interpretations should remain cautious given the exploratory design and absence of a control group. Larger randomized controlled trials are needed to confirm these preliminary findings. Full article

Purpose: This study investigated how variations in approach speed and distance influence lower-limb muscle activation, joint co-contraction ratios (CCRs), and mechanical joint stiffness during single-leg approach run jump landings (ARJSL), to clarify adaptive neuromuscular strategies for joint stiffness regulation. Methods: Twenty-five physically active male university students performed ARJSLs under six randomized conditions combining two approach speeds (fast > 4.0 m/s; slow < 4.0 m/s) and three approach distances (3, 6, and 9 m). Surface electromyography (sEMG) from five dominant-limb muscles—rectus femoris, biceps femoris, tibialis anterior, gastrocnemius, and soleus—was analyzed across three movement phases: pre-activation, downward (braking), and push-off. Knee and ankle CCRs were computed, while kinematic and kinetic data were used to calculate mechanical joint stiffness via inverse dynamics. A two-way repeated-measures ANOVA evaluated the main and interaction effects of approach speed and distance. Results: Significant speed × distance interactions were observed for tibialis anterior activation, several CCRs, and eccentric ankle stiffness (p < 0.05). Pre-activation knee CCR increased with longer, faster approaches, indicating anticipatory joint pre-stiffening. During braking, greater ankle co-contraction under fast–9 m conditions coincided with reduced mechanical ankle stiffness, suggesting a compensatory yielding strategy under high kinetic loads. In the push-off phase, faster approaches elicited higher concentric stiffness at the hip and ankle, supporting efficient energy transfer. Rectus femoris and gastrocnemius activation scaled with both approach speed and distance. Conclusions: Athletes adapt neuromuscular co-contraction and mechanical stiffness in a coordinated, phase-dependent manner to balance protection and performance. These insights may inform targeted training strategies for enhancing jump efficiency and mitigating ACL injury risk. Full article

Background: Participation in soccer imposes high physical, mechanical, and cognitive demands. Recent evidence suggests that cognitive load, often overlooked in injury prevention, interacts with biomechanical factors and injury risk, resembling a dual-task paradigm where players must adapt motor responses while processing unpredictable game situations. This cross-sectional observational study examined how adding a dual-task during single-leg countermovement-jumps (SLCMJ) affects neuromotor control and performance in elite soccer players. Methods: Players performed SLCMJ on the injured leg while muscle activation, kinematics, and kinetics were measured, with and without a dual-task requiring color identification, via repeated-measures ANOVA; three injured groups (Chondropathy, n = 10, ACL, n = 15, Muscle Injury, n = 15) and a healthy control group (n = 22, followed the same protocol during final-rehabilitation stage. Results: Specific main outcomes were kinetics, kinematics, and EMG variables. Kinetic performances were significantly higher (p < 0.001, d > 0.6) with dual-task: eccentric rate-of-force-development, jump-height, reactive-strength-index-modified, and shorter for time-to-peak of ground-reaction-force (p < 0.05, d > 0.6). Muscle activation increased with dual-task in rectus femoris and biceps femoris during pushing (eccentric and concentric phases) (p < 0.01, d = 0.7) and for medial gastrocnemius during landing (p < 0.05, d = 0.7). Kinematic analyses showed greater pushing knee flexion, while pushing and landing trunk flexion was lower (p < 0.01, d > 0.8). Kinetic values in the three injured groups were lower than those of controls (p < 0.01, d > 0.8). Conclusions: Injured elite soccer players appeared disinhibited in dual-task conditions that improved SLCMJ performance but altered neuromotor control, underscoring the importance of a neurocognitive approach in return-to-play assessments to evaluate reinjury risk. Full article

Objectives: An objective evaluation of balance abilities is crucial in research, rehabilitation, sport, and daily life. With ongoing technical advancements, the number of innovative evaluation tools is continuously increasing. This study assessed the methodological quality of various differential balance assessments in young, healthy adults. Methods: Two technically sophisticated balance assessments using a force plate (Single-Leg Landing Test, Single-Leg Squat Test) and a conventional balance assessment using a simple test kit (Y-Balance Test) were applied to 42 students at two different time points. Test–retest reliability, parallel test reliability, and internal consistency were evaluated for each test and item. Results: All tests and (almost) all items showed excellent to acceptable test–retest reliability. In all tests, internal consistency was detected for only some items, while the other items were internally inconsistent. Only a small proportion of tests and/or their items demonstrated acceptable parallel test reliability. The balance performance of the right and left legs showed excellent or good reliability for each item. Conclusions: Significant test–retest reliability and consistency between right and left leg performance suggest good methodological quality of the assessments. The lack of parallel test consistency aligns with previous studies that emphasise the multi-faceted nature of balance tasks, suggesting that balance ability is task-specific rather than a “general ability”. Future studies should investigate and compare the biological and neural backgrounds of differential balance tasks to provide further insights into this topic. Full article

Balance is a key determinant of movement quality and injury prevention in dance, yet targeted dynamic-balance training is rarely embedded in adolescent curricula. This controlled experimental study evaluated a 10-week proprioceptive add-on protocol integrated into Latin American dance practice on neuromotor performance in adolescent female dancers. One hundred twenty-four participants were allocated to an experimental group (EG; n = 62) or a control group (CG; n = 62). Outcomes were the Y Balance Test (YBT; composite and inter-limb asymmetry), Pediatric Reach Test (PRT; anterior and lateral), Single-Leg Landing Stability Test (SLLST; time to stabilization), and countermovement jump (CMJ; bilateral and single-leg). The EG completed 25–30 min of progressive balance work twice weekly before class, while the CG continued standard technical training with matched volume. Compared with the CG, the EG showed clear pre–post improvements in YBT (bilateral composite increased; asymmetry decreased), PRT (anterior and lateral increased), CMJ (bilateral and right single-leg increased), and SLLST (time to stabilization decreased), with significant group × time interactions across domains. Specifically, improvements were significant for Y Balance Test composite scores (p < 0.001), Pediatric Reach Test (p ≤ 0.01), countermovement jump (p < 0.05), and time to stabilization (p ≤ 0.01), confirming robust within- and between-group effects. These findings indicate specific neuromotor adaptations attributable to the integrated protocol. Beyond performance enhancement, the proprioceptive program may contribute to injury prevention, better postural efficiency, and safer execution of complex dance movements in adolescent dancers. Full article

This study systematically evaluated postural control performance on dominant and non-dominant sides in young adults of different sexes using a Third-Order Polynomial Decay fitting method combined with time-domain stability features. A total of 126 participants (66 males, 60 females) performed single-leg landing tasks, during which ground reaction forces (GRF) and center of pressure (COP) data were collected using a Kistler 3D force platform and Bioware acquisition system. Dynamic stability times in the anterior–posterior, medial–lateral, and vertical directions were calculated with polynomial fitting, and additional time-domain measures were used to assess static and dynamic stability. Results showed that on the non-dominant side, participants exhibited significantly longer dynamic stability times (p = 0.015), greater root mean square distance (p = 0.005), and longer total sway path (p = 0.005) in the anterior–posterior direction compared with the dominant side. Significant sex differences were also found in vertical stability index (p = 0.044), dynamic stability index (p = 0.047), total sway path (p < 0.001), anterior–posterior sway path (p = 0.001), and medial–lateral sway path (p < 0.001). In conclusion, the dominant limb demonstrated superior stability, males showed better static control, and females displayed greater dynamic stability, underscoring the importance of targeted non-dominant training and sex-specific balance strategies. Full article

Arch structure is a crucial interface between the human body and the ground during landing tasks, but the biomechanical effects of arch support stiffness remain insufficiently explored. This study examines the effects of arch supports with different stiffnesses on lower-limb biomechanics during landing. Twelve male participants (six normal arches, six flat feet) performed a single-leg drop landing from a 45 cm height under four arch support conditions: no arch support pad (NAP), soft-stiffness arch support pad (SAP), medium-stiffness arch support pad (MAP), and high-stiffness arch support pad (HAP). Dominant lower-limb joint angles and moments in the sagittal plane and vertical ground reaction force (vGRF)-related parameters—time to peak vGRF, peak vGRF, and max loading rate—were recorded using a motion capture system and force plate. Data were analyzed using one-way repeated measures analysis of variance (ANOVA). Arch pad stiffness significantly affected ankle and knee kinematics. The NAP condition exhibited significantly higher ankle plantarflexion at initial contact (p ≤ 0.01), as well as larger range of motion (ROM) of the knee (p = 0.03) and hip (p < 0.01), compared to the use of a SAP or MAP. The use of a HAP resulted in a significantly lower peak ankle dorsiflexion moment and larger peak knee flexion angle than the other conditions (p ≤ 0.04). The peak knee extension moment was the highest when using a NAP, and was significantly higher than that shown with the use of a MAP or HAP (p ≤ 0.02). No significant differences were observed in hip joint moments or vGRF-related parameters across conditions (p ≥ 0.52). These results indicate that hard-stiffness arch support pads modulate lower-limb mechanics during landing, potentially enhancing shock absorption and reducing knee loading. Full article