Human Movement Science

Head-eye coordination during ball interception depends on both task demands and motor experience. The purpose of this study is to determine how these factors influence head-eye contributions to gaze control. Twenty-five female university students (novices with no ball sport experience, n = 13; experienced softball players, n = 12) performed two tasks: visually tracking an approaching ball (tracking task) and, in addition, moving the hand to the ball's landing position (reaching task). Head, eye, and gaze velocities, cross-correlation coefficients between gaze and head velocity, and gaze-head lag time were analyzed using linear mixed models. The results showed that although gaze velocity remained unchanged regardless of tasks or groups, decomposing gaze into head and eye components revealed task-dependent contributions. Compared with the tracking task, the reaching task showed significantly larger head velocity and smaller eye velocity, indicating complementary adjustments that were not revealed by gaze movements alone. The cross-correlation between head and gaze was significantly higher in the reaching task than the tracking task, indicating stronger temporal coupling under greater task demand. Furthermore, the experienced group showed greater task-dependent modulation of eye velocity than the novice group, demonstrating greater flexibility in adjusting the magnitude of head-eye movements to task demands. In addition, the experienced group showed a consistently near-zero gaze-head lag regardless of task, whereas the novice group showed a prolonged gaze-leads-head interval. These findings suggest that ball sport experience shapes two distinct aspects of head-eye coordination: task-dependent flexibility in movement magnitude, and stable, temporally synchronized gaze-head control.

Upright postural control during movement relies on multisensory integration. Yet, the frequency-specific contribution of vision remains poorly characterized in virtual reality (VR). This study investigated how multi-sine visual stimulation amplitude delivered in VR influences standing postural responses. Fifteen healthy adults stood on a force plate wearing a VR headset. Visuo-postural coupling was assessed through coherence and gain analyses between a multi-sine signal (10 sinusoids, 0.12 to 1 Hz) oscillating a virtual environment in one of four amplitudes (0.5, 1, 2, 4 degrees peak-to-peak) and the anteroposterior whole-body angle. All amplitudes elicited measurable postural responses. Increasing amplitude significantly increased postural oscillation and tended to increase coherence, while gain significantly decreased. These results are consistent with a nonlinear control system. The 2 degrees amplitude elicited the largest gain with significant coherence across all stimulated frequencies, suggesting it is suitable for studying visual contributions to postural control during movement execution.

Proprioception can be assessed in several ways, including movement detection, joint position matching, and matching across sensory frames of reference. These task types make different demands, yet they are rarely compared within the same participants on the same device, and psychometric data for wrist-focused batteries are limited. This work had two aims: to compare performance across different levels of proprioceptive judgment, and to establish the within-day test-retest reliability of each. We evaluated three robotic wrist tasks spanning judgments within a single reference frame and across reference frames: joint detection threshold (JDT), same-frame joint-to-joint matching (J-to-J), and cross-frame joint-to-visual matching (J-to-V). Methods. Twenty neurotypical adults completed two identical sessions on the same day, separated by at least two hours, using a single-degree-of-freedom wrist robot. Outcomes were the kinematic detection threshold (degrees) for JDT and the mean absolute matching error (degrees) for J-to-J and J-to-V. Relative reliability was quantified with ICC (2,1) and 95% confidence intervals. Absolute reliability was quantified with the standard error of measurement (SEM) and the smallest detectable change at 95% confidence (SDC 95). Learning effects and differences across task levels were evaluated with paired t-tests or Wilcoxon signed-rank tests. Results. ICC (2,1) was 0.959 [95% CI: 0.900 to 0.980] for JDT, 0.837 [0.640 to 0.930] for J-to-J, and 0.769 [0.500 to 0.900] for J-to-V. The %SEM ranged from 11.9% (J-to-J) to 15.6% (J-to-V). SDC95 was 0.85, 1.71, and 3.54 degrees for JDT, J-to-J, and J-to-V, respectively. A small but significant practice effect was observed for JDT, but this was below the SDC95, and no learning effect was observed for J-to-J or J-to-V. We also observed that the absolute error increased monotonically across task levels, with all pairwise comparisons (JDT < J-to-J < J-to-V; all p < 0.01). Conclusions. All three tasks demonstrated good-to-excellent within-day relative reliability. Error scaled with the computational demand of each task, with the largest errors observed for the cross-frame task, which required a transformation between the visual and joint reference frames. The reported SDC95 values provide task-specific thresholds for distinguishing measurement noise from true change in future intervention studies. Inter-day reliability and validation in clinical populations are the next steps.

[Purpose] By pairing repeated peripheral muscle fatigue induction with a functional and ADL-based assessment, this study tests whether hand muscle fatigue alone is sufficient to im pair fine motor performance in healthy adults performing ADL-inspired tasks. [Participants and Methods] Thirty healthy male and female university students performed 11 tasks twice, once in the pre-fatigue condition and once in the post-fatigue condition. The performance of each task was graded on a 0-4 scale. The score and the time to finish the task (TTFT) were recorded twice, for both the pre- and post-fatigue phases. Maximum force gen eration (MFG) of each participant's grip was recorded prior to the tasks in the pre-fatigue phase and again in the fatigue condition after performing the fatigue protocol. [Results] Muscle fatigue did not have a significant effect on the fine motor performance of the thirty participants, neither (TTFT) nor the scores of each task (p > 0.05) (r=0.08). In contrast, hand muscle fatigue led to a significant decrease in the mean (MFG) for both males and females (p<0.01). [Conclusion] Hand muscle fatigue led to a significant decrease in the mean grip MFG for both sexes. However, this reduction did not translate into impaired fine motor performance during ADL-like tasks. Consequently, under muscle fatigue, hand grip changes during fine tasks tested are rare and have minor to no impact on hand performance. This study suggests that acute peripheral muscle fatigue can coexist with preserved fine motor performance in healthy populations.

In the current experiment, we compared reported perceptual awareness of the visuomotor rotation to motor awareness of changes in reaches established using the process dissociation procedure and drawing task following visuomotor adaptation to a large (50 degrees; R50 group) or a small (30 degrees; R30 group) cursor rotation. Results revealed that perceptual and motor awareness did not differ in magnitude for the R50 group and were significantly correlated. In contrast, while the R30 group perceptually reported being aware of the visuomotor rotation, motor awareness was significantly less and responses were not significantly correlated across tasks. Overall, results suggest that perceptual and motor tasks assess different processes underlying visuomotor adaptation to a small cursor rotation, such that perceptual awareness of the visuomotor rotation is not reflected in reaching performance on tasks assessing motor awareness.

While movement variability is a natural element of human expression, in sign languages it may affect mutual understanding, learning, and potential overuse injury. Sign language variability is not well-understood in part because quantitative analytical methods are yet to be clearly defined. Hence the aim of this study was to assess intra-subject reliability across repeated sessions for three signers, to identify features sensitive to experience-related differences in motor control consistency, and to establish movement consistency metrics for treating sign language kinematic differences as linguistically meaningful. Three signers were assigned to three different proficiency levels of sign language: Deaf (D), proficient (P), and student (S). Sign production variables were evaluated using intraclass correlation coefficients (ICCs) and coefficients of variation(CVs).Most kinematic features showed good to excellent ICCs such as duration, path length, signing space volume, and average and peak velocity. Some EMG features such as mean forearm amplitudes and co-contraction also showed good to excellent ICCs. These data can be used to improve the scientific investigation of sign languages, improve educational resources, and establish baseline thresholds to inform ergonomic or scheduling guidelines for interpreters.

Background: Occupational therapists can improve stroke survivors hand and arm movement and participation in daily activities through action observation (AO). AO involves watching another persons hand or arm complete a movement or task. While research generally supports the use of AO with stroke survivors, there are limited AO videos are available to occupational therapists which makes applying AO challenging. Objective: The purpose of this work is to develop structured and widely accessible tool to support access to AO for stroke survivors, occupational therapists, and researchers. Methods: To develop an AO video library for stroke rehabilitation, functional and non-functional upper limb task deficits were first identified through clinical observations and clinician interviews to establish a prioritized list of daily activities. In collaboration with media production specialists, healthy adult volunteers were recruited and filmed performing these tasks from both first- and third-person perspectives. The recorded videos were then systematically edited, enhanced with instructional title slides, and distributed via a public YouTube channel for clinical application and a categorized digital repository for research purposes. Results: Initial assessments revealed a complete lack of familiarity, awareness, and utilization of AO resources among local occupational therapists, despite high perceived clinical utility. To address this gap, a final library of 150 tasks was established, resulting in the production of 419 finalized, standardized videos featuring six healthy volunteers. For clinical application, these videos were hosted on a free, public YouTube channel organized into 18 functional playlists, while a parallel set was structured into distinct movement categories for research repository storage. Conclusion: By providing a structured and highly accessible tool, this repository enables clinicians, researchers, and caregivers to readily implement evidence-based action observation interventions in both clinical and home settings.

Kinaesthetic motor imagery (kMI) is widely used in sport to enhance motor performance by engaging cortical sensorimotor networks. Neurofeedback may further support kMI, but the optimal neural target to reinforce remains unclear. Maximal sensorimotor event-related desynchronisation (SMR-ERD) represents a relevant target as it may index sensorimotor cortex engagement, yet sport expertise has been associated with reduced SMR-ERD, potentially reflecting neural efficiency. The optimal neurofeedback target may therefore depend on sport expertise, movement expertise, and individual kMI ability. This study examined how these factors influence sensorimotor activity during kMI. We compared 17 basketball players (Experts) and 16 individuals without formal basketball training (Novices). kMI ability and frequency of use were assessed using questionnaires, while SMR-ERD was quantified using electroencephalography (EEG) during kMI. Participants imagined either a basketball-specific movement (Free throw), for which only Experts had extensive experience, or a generic movement (Box lifting), familiar to both groups. Experts reported greater kMI ability and more frequent kMI use than Novices. Only Experts exhibited significant and sustained SMR-ERD during kMI. Moreover, SMR-ERD was stronger in Experts than Novices specifically during Free throw kMI, corresponding to their movement of expertise. Nonetheless, within the Expert group, higher kMI ability was associated with reduced SMR-ERD. These findings suggest that sport expertise initially enhances voluntary recruitment of sensorimotor networks during kMI, whereas greater kMI ability may subsequently promote neural efficiency, resulting in reduced overall sensorimotor cortical activation. These results highlight the need to tailor kMI-based neurofeedback training to users' sport expertise and kMI ability levels.

Cybersickness in virtual reality (VR) arises from conflicts between sensory signals, yet susceptibility varies considerably across individuals. Previous work in this cohort demonstrated that vestibulomotor responses during postural control are associated with cybersickness susceptibility. Here, we examined whether perceptual weighting of gravity, visual, and body cues used to estimate upright orientation is similarly associated with cybersickness and related to previously reported vestibulomotor measures. Thirty-eight healthy young adults (21 females, 17 males) completed a standing VR rollercoaster task while receiving continuous stochastic electrical vestibular stimulation (0-25 Hz, {+/-}4.5 mA). In the current analysis, perceptual cue weights were quantified before and after VR using the Oriented Character Recognition Task. Cybersickness was assessed using the Fast Motion Sickness Scale (FMS), and participants were classified as non-sick (FMS < 5), medium-sick (FMS [&ge;] 5), or high-sick (terminated the VR exposure early due to intolerance). Before VR, non-sick participants exhibited greater gravity weighting (36% vs. 25%) than high-sick participants, whereas high-sick participants showed a non-significant trend toward greater visual weighting (30% vs. 18%). Perceptual cue weights changed minimally following VR, and the magnitude of perceptual reweighting was not associated with sickness severity. Vestibulomotor measures were not correlated with perceptual gravity weighting, and postural sway during VR was not associated with visual weighting. These findings suggest that greater baseline perceptual gravity weighting, rather than short-term perceptual reweighting, is associated with reduced cybersickness susceptibility. The dissociation between perceptual and vestibulomotor measures suggests that orientation perception and postural control reflect partially distinct multisensory integration processes. New and NoteworthyThis study demonstrates that baseline perceptual gravity weighting is associated with susceptibility to cybersickness during virtual reality exposure with concurrent electrical vestibular stimulation. Greater reliance on gravity cues was associated with reduced susceptibility, whereas visual weighting showed a similar but non-significant trend and perceptual reweighting changed minimally following exposure. Perceptual measures were dissociable from vestibulomotor responses, suggesting that orientation perception and postural control reflect partially distinct multisensory integration processes.

Conventional transfemoral amputation disrupts native neuromuscular pathways, limiting prosthetic joint control, sensory feedback, and the perception of the prosthesis as part of the body. To ameliorate these pathologies, we restored the agonist-antagonist relationship of residual muscles in two individuals with above-knee amputation through an interventional surgical revision. Participants trained with a bionic knee prosthesis before and after the surgical revision while generating neuromuscular, cortical, functional, and affective data. Both individuals demonstrated improvements after the revision that could not readily be attributed to training effects, including: 1) increased proprioceptive afferents and stronger activation in cortical regions associated with sensorimotor integration of their missing joints, 2) improved control of the bionic knee during functional tasks including sit-to-stand and stair ascent, and 3) generally greater prosthesis embodiment, proprioception, and phantom limb definition as assessed through questionnaires and interviews. In contrast, training outcomes were more participant-specific and more variably correlated with amount of exposure, especially before the revision. These pilot findings suggest that revisional augmentation of residual neuromuscular tissues to restore agonist-antagonist dynamics may promote sensorimotor coherence and enhance both functional and perceptual integration with a bionic prosthesis, and remaining participant-specific heterogeneities may be attributable to inter-individual difference in residual limbs neuromuscular system, amputation history, and personal beliefs about prosthesis usage.

BackgroundExplosive force generation during the initial acceleration phase is critical for successful base stealing in baseball. Preparatory balance control preceding movement onset may facilitate this process by constraining horizontal ground reaction force (GRF) toward a task-specific direction. However, its contribution to ballistic sprint initiation remains unclear. Research questionDoes preparatory force constraint influence explosive force generation during base stealing, and when during the preparatory phase is this influence greatest? MethodsFourteen baseball players performed 3-m maximal sprints simulating base stealing under time-constraint (Time) and self-paced (Self) conditions. GRF around movement onset were recorded. Peak rate of force development (peak RFD) was computed from onset to take-off. A 250-ms window before the onset was divided into 50-ms bins, and mean resultant length (Rlen), which represents the extent of force constraint, of each bin was calculated. Using statistics analyses, Differences between conditions were tested, and the relationship between the interaction (Rlen x condition) and peak RFD was assessed. ResultsThe peak RFD was greater under the Self condition than under the Time condition, accompanied by a larger Rlen. Furthermore, Results indicated that the force constraint in the 150-100 ms interval preceding the movement onset most strongly influenced the peak RFD. SignificanceThese findings demonstrate that temporally organized preparatory force constraint plays a critical role in explosive sprint initiation during base stealing. Identifying the specific preparatory timing linked to superior force production provides novel mechanistic insight into preparatory balance control and may inform targeted training strategies for ballistic athletic movements.

Learned movements are thought to be represented in both extrinsic and intrinsic coordinate systems. Intrinsic representations have traditionally been characterized using joint-based coordinates, although the relationship between joint movements and muscle activation depends strongly on limb configuration. Consequently, movement directions aligned in joint space may not be aligned in muscle space, but the implications of this mismatch for motor learning have remained largely unexplored. We addressed this question by combining electromyographic (EMG) analysis with a visuomotor adaptation experiment. In Experiment 1, participants performed planar reaching movements in two workspaces separated by a 45{degrees} shoulder rotation while EMG activity was recorded from nine upper-limb muscles. Muscle-pattern similarity analysis revealed that movement directions aligned in joint space were not always aligned in muscle space and that the degree of misalignment varied systematically across movement directions. Based on these results, we predicted that visuomotor adaptation to clockwise (CW) and counterclockwise (CCW) rotations would produce different patterns of motor generalization, contrary to the prediction of conventional joint-space accounts. Experiment 2 confirmed this prediction, revealing a systematic shift between the CW and CCW generalization patterns that was consistent with the muscle-space prediction. These findings suggest that intrinsic representations of learned movements are not fully captured by joint-based coordinates alone and that muscle-based coordinates contribute to motor learning and its generalization. Together, these findings highlight the importance of considering underlying biomechanics when interpreting motor representations using generalization paradigms.

This study examined how tempo, dynamics, and string influence upper-extremity physical exposure in professional violinists and how exposure variability is distributed among musical characteristics, between-subject differences, and residual variability. Twelve violinists performed seven standardized scales while bilateral upper-arm and wrist kinematics and shoulder and forearm muscle activity were recorded. Linear mixed-effects models showed that faster tempo increased right upper-arm velocity and bilateral forearm activity while reducing right upper-arm and wrist ranges of motion. Louder dynamics increased bilateral forearm and right trapezius activity and right-wrist ranges of motion. Higher-posture strings increased right upper-arm elevation and right shoulder muscle activity. Variance analysis identified exposures predominantly related to musical characteristics, jointly related to musical characteristics and between-subject differences, predominantly related to between-subject differences, or mainly unexplained. These findings support future exposure prediction from musical characteristics and targeted prevention through repertoire-based workload management, structured recovery, and individualized technique-focused strategies.

The ability to accurately perceive arm position is essential for motor control and depends on the integration of proprioceptive and visual information. However, how lifelong visual impairment (VI) affects position sense and its neural correlates remains unclear. We quantified arm position sense and associated cognitive-motor load in right-handed visually impaired (n = 7) and normally sighted (NS; n = 7) individuals using three bilateral arm position matching tasks: joint angle matching (JAM; internal coordinates), hand direction-distance matching (DDM; external coordinates), and mirror direction-distance matching (MDDM; external coordinates kinematically identical to JAM). Cognitive load was assessed using the contingent negative variation (CNV) from EEG recordings. VI participants exhibited reduced accuracy and precision of arm position sense in most conditions, and greater CNV magnitude, particularly in the left parietal cortex. Across both groups, performance was worse and CNV magnitude was greater in the DDM task compared with JAM, whereas JAM and MDDM yielded similar behavioral and neural outcomes. These findings indicate that (i) visual experience enhances arm position sense, and (ii) representing limb position in external coordinates imposes greater cognitive demands than encoding joint-based posture. The similarity between JAM and MDDM suggests that participants preferentially rely on internal representations when task kinematics permit.

Physiological mirror activity (pMA) is the increase in involuntary muscle activity observed on the contralateral side during unilateral voluntary movement in neurologically healthy participants. This cross-sectional study aimed to explore the relationship between pMA and corticomuscular coherence (CMC) during finger dexterity tasks in young and older adults. Thirty-one right-handed young adults and 24 older adults performed a left-hand finger dexterity task. Electroencephalogram (EEG) signals were recorded from C3 and C4, and electromyogram (EMG) signals were collected from bilateral finger flexors and extensors. pMA was quantified as the change in right-hand EMG from rest to task. Gamma-band CMC was calculated from task-related EEG-EMG pairs, and its association with pMA was analyzed. In young adults, greater pMA was associated with lower CMC (C3- and C4-right flexors), whereas in older adults, greater pMA was associated with higher CMC (C3-left flexor). Young adults may suppress pMA emergence by appropriately monitoring and inhibiting activity, in the hand not performing the task. Conversely, in older adults, the mobilization of the ipsilateral motor cortex may have contributed to pMA emergence. This study suggests that the neuromuscular mechanisms involved in pMA during finger dexterity tasks differ between young and older adults.

Importance: There are very few interventions designed for individuals with the most severe mobility impairments. Robotic walking may be an effective way to facilitate exercise in this population. Objective: To examine how robot-assisted walkers physical parameters and user characteristics moderate the exercise intensity achieved by individuals with neuromotor disorders causing mobility impairments. Design: A prospective study. Intervention: A single-session intervention involving an overground robot-assisted walker that can be used in an endurance mode requiring no voluntary movement or a strength mode during which voluntary movement could impact the gait pattern. Participants: Individuals with pediatric-onset mobility impairments Main Outcome Measures: Participants were characterized based on their age, sex, diagnosis, and Gilette Functional Assessment Questionnaire (FAQ) levels. Heart rate during the final minute of four 5-minute walking conditions: strength mode at fast speed, strength mode at slow speed, endurance mode at fast speed and endurance mode at slow speed was expressed as a percentage of each participant heart rate reserve (%HRR). Linear mixed-effects models were used to evaluate the impact of speed, device mode and user characteristics on the level of exercise achieved. Results: 29 individuals (aged 2-26 years) with mobility impairments (FAQ levels 1-6) completed this study. Fast speeds were associated with a higher %HRR (beta= 2.11, SE = 1.03, p = 0.044). Participants in FAQ class 1 exhibited significantly higher %HRR compared with those in FAQ classes 2 and 3 (beta=18.6, SE=7.31, p=0.017; beta= 16.9, SE = 8.13, p = 0.047, respectively). No other device or participant characteristics were associated with exercise intensity. Conclusions: To facilitate higher exercise levels, users of robot-assisted walkers can increase their speed. Individuals who cannot take steps due to their neuromotor impairments experience the highest levels of exercise. Relevance: The findings in this study highlight the promise of robot-assisted walkers to improve health, particularly in those who often face the greatest barriers to exercise.

Limb-trunk coordination plays an essential role in daily actions. The reticulospinal excitability of limb muscles has been suggested to be modulated by long-term motor experience, such as strength training. However, it remains unclear whether reticulospinal contributions in the limb and trunk muscles during limb-trunk coordinated movements are modulated by strength training. This study aimed to determine whether reticulospinal contributions to limb-trunk coordination differ between strength-trained and untrained individuals. Fifteen long-term ([&ge;]3 yrs) strength-trained and 15 untrained healthy men participated in this study. Participants performed a rapid bilateral arm-curl task while standing, using a load corresponding to 35% of their one-repetition maximum, in response to visual, visual-auditory (80 dB), or visual-startling (115 dB) stimuli. Electromyography (EMG) was recorded from the right biceps brachii (BB) and erector spinae (ES) muscles during the task. In the trained group, EMG onset of the ES was closer to that of the BB than in the untrained group, indicating tighter temporal coordination between the limb prime mover and trunk postural muscles in strength-trained individuals. In both groups, visual-startling stimuli shortened the EMG onset of both the BB and ES, suggesting reticulospinal contributions to both muscles. Notably, the reduction in EMG onset of the BB induced by the startling stimulus was smaller in the trained group than in the untrained group, whereas no difference between groups was observed for the ES. These findings suggest that long-term strength training may modify limb-trunk muscle coordination during standing arm curls and may be associated with muscle-specific adaptations in reticulospinal contributions.

Background and Purpose: Walking after stroke is often characterized by persistent biomechanical impairments and reduced walking capacity. While visual biofeedback can improve gait mechanics and fast walking can enhance capacity, it is unclear whether individuals post-stroke can effectively use biofeedback at higher walking speeds to address both deficits simultaneously. This study examined the effects of walking speed on the ability of participants with chronic stroke to reduce step length (SL) errors using visual biofeedback. Methods: Sixteen individuals with chronic stroke walked on a treadmill at slow, self-selected, and fast speeds with and without visual SL biofeedback. Absolute SL error relative to individualized targets was calculated for paretic and non-paretic limbs. Linear mixed-effects models with piecewise linear splines assessed the effects of speed, limb, and feedback condition. Post hoc comparisons were performed for significant interactions. Results: At lower speeds, increasing speed reduced SL error in both limbs (p < 0.001). At higher speeds, the effects of speed were dependent on limb and condition (p < 0.001). Paretic SL error increased with speed without feedback but remained stable with feedback (p < 0.001). Non-paretic SL error decreased with speed regardless of condition. SL error was greater in the paretic limb overall (p < 0.001). Discussion and Conclusions: Fast walking alone did not reduce paretic SL errors. Participants with chronic stroke can effectively use visual biofeedback to reduce paretic SL errors at higher speeds, supporting its integration into high-intensity gait training to simultaneously treat biomechanical impairments and walking capacity deficits after stroke.

Certain features of everyday motor skills become automatic while others remain controlled. Here we use a novel keyboard typing task to investigate whether motor automaticity depends on the frequency of naturally learned motor sequences. Participants type five-letter strings that vary in their word and bigram (two-letter sequence) frequency in natural language, allowing us to examine the influence of prior exposure without laboratory training. Novel pseudo word strings are tested as well. We find greater sequence frequency in natural language is associated with faster inter-keypress intervals and lower temporal variability within the sequence. In contrast, latencies to initiate a sequence are slower for novel pseudo-word strings but are otherwise insensitive to natural word frequency. We also find individual differences in inter-keypress speed and variability are robust across frequency levels but are unrelated to conventional measures of typing skill. Our method establishes keyboard typing as a scalable, ethologically valid framework for probing features of a naturally acquired human motor skill. This research will help extend laboratory-based studies of motor sequence learning and sets the stage for future investigations of linguo-motor processes. Moreover, our findings demonstrate which features within naturally acquired motor sequences become automatic and that typing proficiency is not determined solely by automaticity.

Knee flexion contracture (KFC) may occur in the late stages of arthropathies, including osteoarthritis and haemophilic arthropathy. The impact of KFC on neuromuscular control remains unclear, particularly for the affected ankle plantar flexors. Surface electromyography (EMG) is widely used to assess muscle activation patterns, whereas intermuscular (EMG-EMG) coherence provides insight into common neural input. In this study we compared the neural control of ankle plantar flexors during gait between individuals with haemophilia and KFC (chronic; n = 8), and healthy individuals without (control; n = 15) and with an artificial constraint (artificial; n = 15). Bipolar EMG from plantar flexors was recorded during 30-m overground walking (1 m/s). Intermuscular coherence was estimated at 8-60 Hz during the stance phase and significance was determined using a permutation method. The chronic group showed greater knee flexion than controls (24-29 deg vs 2-20 deg), higher EMG amplitude at foot contact, and increased intermuscular coherence in the alpha (8-12 Hz) and beta (12-30 Hz) bands at mid-stance. Despite comparable sagittal knee kinematics between constrained conditions (chronic: 24-29 deg; artificial: 20-32 deg), early-stance EMG amplitude and mid-stance beta-band intermuscular coherence were higher in the chronic group across plantar-flexor pairs. Increased plantar-flexor activation in the chronic group suggests higher neural drive, while higher intermuscular coherence reflects greater common input to the plantar flexors. These findings indicate that limited ROM alone does not explain the altered neural control of plantar flexors, suggesting neural adaptations associated with non-neurological chronic KFC.