Human Movement Science

Patients recovering from hemiparetic stroke have been shown to benefit from mirror therapy in terms of improving their motor function. The clinical improvement in motor function may differ depending on the mirror therapy protocol used. Previous studies have shown that four parameters are influential: the size of the mirror (large and small), manipulation of objects (with or without), the complexity of action (simple and complex), and movement execution (unilateral and bilateral). We examined the impact of these parameters on the subjective quality (believability) of the mirror illusion in unimpaired participants. Forty healthy participants completed 16 different combinations of the four parameters during mirror visual feedback. Participants rated each trial for its level of believability on a 10-point Likert scale. A repeated measures ANOVA was used to examine the data. The large mirror consistently elicited higher ratings than the small mirror. And while bimanual movements generally elicited higher ratings than unimanual movements, ratings for bimanual movements were significantly reduced when participants made complex movements with objects. We attributed these results to the congruency of multisensory information. Conditions that elicit congruency between illusory information and other sensory inputs appear to maximise believability over the illusory hand. The findings of this study reveal the parameters maximising illusion believability in unimpaired participants and have implications for optimal mirror therapy conditions in patients groups.

A subset of bilateral tasks requires one arm to perform a stabilizing role while the other completes a movement, such as slicing a loaf of bread. Visual attention during bilateral tasks has previously been examined with bilateral reaching tasks, demonstrating that visual attention switches between the two target locations. The goal of this study was to characterize visual attention during a cooperative mechanically coupled bilateral "stabilizing and reach" task to determine how visual attention is divided between the two limbs when one limb plays a stabilizing role. Twenty-six healthy young adults completed a robotic task in which the hands were coupled with a haptic spring. Participants were instructed to keep one hand stationary in a target while they reached for a target with the other hand, thus stretching the spring and applying a force to both arms. We found that individuals primarily fixated their gaze on the reaching target, only fixating on the stabilizing target for approximately 10% of the reaching time. Longer fixations on the reaching target were associated with faster reaching times, while longer fixations on the stabilizing target were associated with slower reaching times. While the performance of the stabilizing hand differed between the dominant and non-dominant limbs, visual strategies did not vary based on which hand was stabilizing. These results demonstrate that unlike bilateral reaching tasks in which the eyes frequently saccade between the two targets, visual guidance is primarily used for the reaching hand while minimal overt visual attention is directed to the stabilizing hand.

BackgroundDuring hand reaching movements in people with stroke, the coordination of trunk, shoulder, and elbow muscles changes as a function of target height. However, it is not known whether target height also influences non-use, defined as the difference between two coordinations aiming at the same target. MethodsTwenty-two individuals with stroke (> 1 month) completed the Proximal Arm Non-Use (PANU) test in two conditions: high target (80 cm) and low target (67 cm). Elbow, shoulder, and trunk use was recorded using motion capture. ResultsTrunk compensation and non-use of the shoulder and elbow joints were found to depend on target height. ConclusionsBecause trunk bending forward goes against the need to elevate the hand, a sufficiently low target is necessary to unmask the presence of shoulder-elbow non-use. We provide novel recommendations for assessing compensations and non-use during hand reaching. Clinical Trial: NCT04747587.

The evolution of virtual reality (VR) has created the opportunity for a relatively low-cost and accessible method to practice motor skills. Previous studies have demonstrated how motor skill practice in non-immersive virtual environments transfers to physical environments. Though minimal research has investigated motor learning and transfer within immersive VR, multiple experiments provide empirical evidence of positive transfer effects. To enhance the similarities between virtual and physical environments, most studies have used software engines and modified hardware. However, many learners and practitioners are currently using commercially available VR with the goal of enhancing real-world performance, though there is very little evidence to support the notion of positive transfer for these systems. Therefore, the purpose of this experiment was to investigate how motor skill practice using a commercially available VR system improved real-world performance and how that compared to physical practice. Participants (n = 68) were randomly selected into one of two groups: virtual reality (VR) practice (n = 33) or real-world (RW) practice (n = 35). The experiment took place over two consecutive days with a pretest, posttest, and practice phase occurring on both days. The pre- and post-testing phases were identical for both groups and consisted of putting a golf ball 10 times on a carpeted surface towards the center of a target. The practice phases consisted of 60 total putts per day in the respective environment (VR or RW). Participants continuously alternated golf putting holes from three different distances until they accrued 60 total putts. Participants in the RW group performed golf putts to three targets. Participants in the VR group also performed golf putts on three different miniature golf putting holes, using the commercially available Oculus Rift and the Cloudlands VR Minigolf game. The VR putting targets were designed to replicate the putting holes in the physical environment. Separate 2 (condition) x 4 (test phase) repeated measures ANOVAs were used to assess accuracy and club head kinematics. The results revealed a significant main effect for test phase, but not for condition. Post hoc analyses revealed both groups significantly improved their putting accuracy and club head kinematics at similar rates. The results from this study indicate that the transfer of learning that occurred from the commercially available VR practice was equally effective when compared to RW practice.

The ability to self-evaluate motor performance or estimate performance errors is beneficial for motor learning or relearning in the context of neurologic injury. Some evidence suggests those with injury like stroke may be unable to accurately self-evaluate their performance; however, it is unclear if individuals who are absent of injury are accurate in this domain. We aimed to investigate the accuracy of self-evaluation and potential influencing factors by conducting a systematic search to identify literature involving the self- and objective-evaluation of upper-extremity motor tasks. Twenty-three studies satisfied inclusion criteria. Data revealed a moderate positive correlation between self- and objective evaluations across a variety of tasks, from trivial button pressing to specialized surgical suturing. Both under- and overestimation of performance was found across the papers. Key factors identified to influence the accuracy of self-evaluation were the task purpose, familiarity, difficulty, and whether an individual received a demonstration. This review identified some limitations in this field of research. Most notably, we found that very few studies have investigated the accuracy of self-evaluation of motor performance with the primary goal of comparison to objective performance. Many studies reported the data but did not make direct statistical comparisons. Moreover, due to inconsistencies between how self and objective-evaluations were conducted, we argue that in this area of investigation self-evaluation tools need to replicate the objective evaluation method, or at minimum the self-evaluation tool should ask questions specific to the construct of performance that is being measured objectively.

BACKGROUNDAutistic Spectrum Disorder (ASD) presents with a multitude of problems such as physical, social, emotional, psychological, etc. Most common physical problems are impairments in standing balance and posture. It is unknown whether these impairments have any association between tactile sensation or are purely due to deficits in sensory processing and integration. We hypothesized that foot tactile sensation in ASD is positively correlated to performance in standing balance as measured by Pediatric Balance scale. METHODSThe data collected at Heartshare Human Services of New York was used for secondary analysis. It consisted of 12 participants and included: 1. Muscle and joint ROM testing to rule out any muscle involvement in balance problems. 2. Tactile sensation testing at four sites on sole of foot bilaterally using Semmes Weinstein monofilament. 3. Pediatric Balance Scale (PBS) for balance testing. RESULTSWe found significant positive correlation between cutaneous tactile sensation (SWF) and Pediatric Balance scale (PBS) measures in our participants i.e., reduced tactile sensation was moderately associated with impaired balance score. CONCLUSIONSWe propose that during conventional clinical assessment for individuals with ASD, foot tactile sensation should not be overlooked, and included as a part of somato-sensory assessment. In addition, enhancing foot tactile sensation could also be used for targeted interventions to improve balance in children with ASD.

The action/perception theory of cortical organization is supported by the finding that pantomime hand movements of reaching and grasping are different from real movements. Frame-by-frame video analysis and MATLAB(R) based tracking examined real/pantomime differences in a bilaterally movement, string-pulling, pulling down a rope with hand-over-hand movements. Sensory control of string-pulling varied from visually-direct when cued, visually-indirect when non cued and somatosensory controlled in the absence of vision. Cued grasping points were visual tracked and the pupils dilated in anticipation of the grasp, but when noncued, visual tracking and pupil responses were absent. In real string-pulling, grasping and releasing the string featured an arpeggio movement in which the fingers close and open in the sequence 5 through 1 (pinki first, thumb last); in pantomime, finger order was reversed, 1 through 5. In real string-pulling, the hand is fully opened and closed to grasp and release; in pantomime, hand opening was attenuated and featured a gradual opening centered on the grasp. The temporal structure of arm movements in real string-pulling featured up-arm movements that were faster than down-arm movement. In pantomime, up/down movements had similar speed. In real string-pulling, up/down arm movements were direct and symmetric; in pantomime, they were more circular and asymmetric. That pantomime string-pulling featured less motoric and temporal complexity than real string-pulling is discussed in relation to the action/perception theory and in relation to the idea that pantomimed string-pulling may feature the substitution of gestures for real movement.\n\nSignificant StatementMost laboratory studies investigating hand movements made by humans feature single hand movements, the current study presents a novel string-pulling task to study bimanual coordination of left and right hands in real and pantomime conditions. The results show that pantomime string-pulling featured less motoric and temporal complexity than real string-pulling. These findings are relevant to the contemporary theory of action and perception that the dorsal stream (parietal cortex) is related to actions and the ventral stream (temporal cortex) is related to perception.

Combined action observation and motor imagery (AOMI) facilitates corticospinal excitability (CSE). This study used single-pulse transcranial magnetic stimulation (TMS) to explore changes in CSE for coordinative AOMI of a single-leg sit-to-stand (SL-STS) movement. Twenty-one healthy adults completed two testing sessions, where they engaged with baseline (BL), action observation (AO), and motor imagery (MI) control conditions, and three experimental conditions where they observed a slow-paced SL-STS while simultaneously imagining a slow- (AOMIHICO), medium- (AOMIMOCO), or fast-paced (AOMILOCO) SL-STS. A TMS pulse was delivered to the right leg representation of the left primary motor cortex at three stimulation timepoints aligned with peak EMG activity of the knee extensor muscle group for the slow-paced (T3), medium-paced (T2), and fast-paced (T1) SL-STS during each condition. Motor evoked potential (MEP) amplitudes were recorded from the knee extensor muscle group as a marker of CSE for all stimulation timepoints and conditions. A main effect for experimental condition was reported for all stimulation timepoints. MEP amplitudes were significantly greater for AOMIHICO at T1 and T3, and AOMIMOCO and AOMILOCO at all stimulation timepoints, when compared with control conditions. This study provides neurophysiological evidence supporting the use of coordinative AOMI as an alternative method for movement (re)learning.

The human shoulder likely evolved under selective pressures favouring diverse tasks that require high mobility, speed, and torque. For example, humans are uniquely adept at high-speed and accurate throwing. Prior work has aimed to quantify the kinematics and kinetics of upper limb movements in isometric or uniplanar motions. However, we still do not fully understand the trade-offs of shoulder torque and power with angular velocity during functional tasks that are reflective of demands that may be relevant to the shoulders evolution. We developed a novel approach for upper limb 3D inverse dynamic calculations by integrating motion capture with an instrumented cable machine. Twenty-five participants performed a crossbody, isokinetic upper limb motion at various cable speeds in a rigid and free torso condition (self-imposed). Shoulder torque decreased significantly (p < 0.05) with increasing angular velocity in 19 and 16 participants for the constrained and unconstrained conditions, respectively. Shoulder power increased significantly (p < 0.05) with angular velocity for 6 and 11 participants for constrained and unconstrained, respectively. T-tests revealed no statistical difference between the torso conditions for torque and power against angular velocity. Our findings suggest that despite having a trade-off in torque and velocity, the shoulder may be tuned to produce power over a wide range of velocities independent of energy transfer from the lower extremities.

Degraded vision (caused by pathological reasons or monocular viewing) has been shown to affect fine motor control. However, there is a dearth of work examining the effects of "cataract-like" blur on reach-to-grasp performance. There is, however, a trend towards amblyopic blur being associated with deficits in reach-to-grasp performance, suggesting that timely intervention in treating cataracts is likely to be essential to maintain a functional ageing population. 18 participants performed a reach-to-grasp task. They reached for and precision grasped high and low-contrast cuboid targets under three visual conditions: binocular blur, monocular blur (full vision in the other eye) and full vision. They also performed contrast sensitivity, stereoacuity and visual acuity tests. Visual blur was associated with changes to the kinematics of prehensile movements early/acceleration stage (maximum acceleration and maximum velocity) and maximum grip aperture. Visual blur also caused the period from first contact with the target to the time it was lifted (dwell time) to be elongated. These results suggest that changes in prehension associated with visual blur are linked to differences in the planning and online control of prehension movements.

BackgroundSensory information processing plays a crucial role in monitoring the timing of external and internal events, including the control of balance. While previous research has investigated the role of vision in the perceived timing of postural instability onset with eyes closed and open, it is important to further explore the influence of visual context. Virtual reality offers a unique opportunity to manipulate visual information and assess its impact on balance control and the perceived timing of sensory events. Research QuestionDoes visual information, particularly visual threat presented in virtual reality, alter the perceived timing of postural instability onset? MethodsTwo temporal order judgment tasks were conducted using virtual reality to manipulate visual information. Participants were placed on a virtual skyscraper to induce visual threat. The experiments investigated the impact of visual information on the perceived onset of postural instability while manipulating the presence/absence of visual threat. ResultsWith vision available but without visual threat, the onset of a postural perturbation needed to occur 10.71-12.33 ms before a reference sound stimulus to be perceived as simultaneous. With visual threat, the onset needed to occur 4.45 ms before auditory cue onset to be perceived as simultaneous. While these delays were not significantly different from true simultaneity of perturbation and sound onset, participants were significantly more precise in their judgments when threatening visual information was present. SignificanceOur results show that visual context, particularly visual threat presented in virtual reality, may alter the perception of perturbation onset and the precision of judgments made. This has implications for understanding the role of vision in balance control and developing interventions to improve balance and prevent falls.

Human bipedal posture is inherently unstable, making even daily activities potentially lead to falls and serious injuries. Although prior studies have shown that appropriate postural control supports both task success and postural balance during quiet standing or under modest postural demands, it remains unclear how the central nervous system controls whole-body posture under high-demand, near-fall conditions. Here, we investigated how varying postural demands influence postural strategies using a whole-body task in which participants leaned their body mediolaterally to reach a target. We manipulated the required leaning angles and velocities by varying target positions and time constraints to reach a target, thereby introducing different levels of postural demand. The results demonstrated that target position, time constraint, and movement distance significantly affected task performance, defined as reaching accuracy. Specifically, participants could accurately reach targets requiring upright or moderately leaning postures. However, when targets required greater leaning postures, participants failed to reach them. Furthermore, the detrimental effects of shorter time constraints and longer movement distances on task performance became more pronounced when target positions required greater leaning postures. These findings suggest that the central nervous system tolerates low to moderate postural demands to achieve task goals. In contrast, when postural demands exceed a certain threshold, the central nervous system begins to prioritize postural safety over task success. This study highlights the nonlinear effect of postural demands on motor planning during whole-body movements.

People with amputation walk asymmetrically, leading to increased risk of intact leg injury. Split-belt treadmill walking using error augmentation has potential to correct this asymmetry. The purpose of this study was to assess how people with trans-tibial amputation and matched control subjects would adapt their limb forces to gradual onset split-belt treadmill walking. Consistent with prior split-belt results in sudden onset split-belt walking, we hypothesized that, after gradual onset split-belt walking, people with trans-tibial amputation and intact controls would display aftereffects in braking force but not propulsive force. We also hypothesized that both groups would have aftereffects in step length symmetry and double support, indicating predictive control of inter-leg coordination. People with trans-tibial amputation and control subjects displayed aftereffects in braking force, propulsive force, double support time, and step length symmetry. People with trans-tibial amputation displayed an aftereffect in step length opposite their baseline asymmetry. Both subject groups had aftereffects in fast (intact) leg forces that were larger for braking and smaller for propulsive forces than baseline. These findings indicate that gradual onset split-belt adaptation involves predictive control of inter-leg coordination and leg forces, which is not impaired by trans-tibial amputation. Predictive control of step length and braking is consistent with prior work, but these results suggest different adaptive control of propulsion than prior sudden onset research. This study shows that gradual onset split-belt walking may correct step length asymmetries in people with trans-tibial amputation, but increased intact leg braking aftereffects has potentially negative implications for correcting amputation-related kinetic asymmetries.

BackgroundTraumatic brachial plexus injury (TBPI) causes a sensorimotor deficit in upper limb (UL) movements. ObjectiveOur aim was to investigate the arm-forearm coordination of both the injured and uninjured UL of TBPI subjects. MethodsTBPI participants (n=13) and controls (n=10) matched in age, gender, and anthropometric characteristics were recruited. Kinematics from the shoulder, elbow, wrist and index finger markers were collected while upstanding participants transported a cup to mouth and returned the UL to a starting position. The UL coordination was measured through the relative phase (RP) between arm and forearm phase angles and analyzed as a function of the hand kinematics. ResultsFor all participants, the hand transport had a shorter time to peak velocity (p<0.01) compared to the return. Also, for the control and the uninjured TBPI UL, the RP showed a coordination pattern that favored forearm movements in the peak velocity of the transport phase (p<0.001). TBPI participants injured UL showed a longer movement duration in comparison to controls (p<0.05), but no differences in peak velocity, time to peak velocity and trajectory length, indicating preserved hand kinematics. The RP of the injured UL revealed altered coordination in favor of arm movements compared to controls and to the uninjured UL (p<0.001). Finally, TBPI participants uninjured UL showed altered control of arm and forearm phase angles during the deceleration of hand movements compared to controls (p<0.05). ConclusionThese results suggest that UL coordination is reorganized after a TBPI so as to preserve hand kinematics.

Navigating public environments requires adjustments to ones walking patterns to avoid stationary and moving obstacles. It is known that physical inactivity induces alterations in motor capacities, but the impact of inactivity on anticipatory locomotor adjustments (ALA) has not been studied. The purpose of the present study was to compare ALAs and related muscle co-contraction during a pedestrian circumvention task between active (AA) and inactive young adults (IA). Thirteen AA and thirteen IA were placed in a virtual environment simulating a public park. Participants circumvented virtual pedestrians walking towards them. Walking speed, onset of deviation, clearance, foot placement strategies and muscle co-contraction were analysed. IA exhibited slower walking speeds compared to the AA during circumvention condition but not during unobstructed walking condition. The distance at the onset of trajectory deviation was larger for IA. Both groups increased co-contraction for pedestrian circumvention at the ankle and left hip and IA displayed greater ankle co-contraction overall. No significant group differences were observed in minimum clearance. This study suggests that an inactive lifestyle influences ALAs by inducing a cautious behavior during pedestrian circumvention.

Laboratory experiments employing robotic manipulandum are far from achieving their goal of helping people improve their motor learning. Remote experiments using web applications are an effective tool for bridging the gap between robotic manipulandum experiments in the laboratory and general motor tasks outside. However, the influence of interventions that increase error or variability in remote motor tasks on motor learning has not yet been determined. In this study, we aimed to elucidate the effects of interventions that visually increase errors and variability in remote experiments using web applications. In particular, 48 people participated in a web-based study on the cursor-manipulation of motor tasks using laptops. Three motor tasks (visuomotor-rotation reaching, virtual curling, and virtual ball-throwing tasks) were conducted, and each task consisted of 120 trials a day conducted for three days in this study. For each task, no intervention was provided on Day 1 and the intervention to augment motor error or variability was provided on Days 2 and 3. Differences between the groups in post-intervention test trials were examined using statistical analyses. Contrary to our expectations, the interventions of error-augmentation did not exhibit positive effects in Experiments 1 and 2, which could be attributed to a lack of haptic and proprioceptive information or inaccuracies in movement kinematics. In addition, the interventions of variability-augmentation did not exhibit positive effects in Experiment 3, which could be attributed to the complex dynamics in the relationship between perceived body movements and motor outcomes. Further research is required to identify the differences between the conditions when the interventions are effective or ineffective. Moreover, interventions must be developed to further improve general motor skills.

Walking is an attentionally demanding process that draws from a limited pool of attentional resources. Dual-task assessments, where individuals perform a cognitive task while walking, often reveal changes in gait and balance due to competing attentional demands. As cognitive task difficulty increases, the attentional resources necessary to complete the task also increase, leading to greater interference with gait and balance. However, these interactions are typically examined using contrived lab-based tasks, leaving it unclear how the cognitive processes engaged during real-world movement impact walking. In the present study, we investigated whether increasing the attentional demand of spatial navigation, a cognitive process intrinsically linked to movement, interferes with gait and balance. Healthy adults completed an ambulatory virtual reality homing task in which they walked through a virtual environment and navigated to previously visited locations while wearing ankle and lumbar trackers. We increased the attentional demand of navigation by removing sensory cues during this homing phase: full cues, visual cues only, or self-motion cues only. Navigation performance declined as sensory cues were removed, but we observed no corresponding changes in their spatiotemporal gait and balance metrics. These results show that, in healthy adults, increasing the attentional demand of spatial navigation does not interfere with gait and balance during real-world movement. This finding suggests that locomotor control may be robust to navigation-related cognitive demands. Further research is needed to determine why navigation did not interfere with mobility and to clarify the relationship between these two interconnected processes.

Intact ankle proprioception is essential for the control of balance and gait. This study determined ankle position sense acuity for plantarflexion and dorsiflexion. In two separate assessments, the right ankle of 30 healthy young adults was passively rotated from neutral joint position to a 15{degrees} reference position and a smaller comparison position in either plantar- or dorsiflexion. Subsequently, participants verbally indicated which position felt more flexed. After 25 trials, a psychometric function was fitted to the respective response-stimulus size difference data for each participant and two outcome measures were derived: a Just-Noticeable-Difference (JND) threshold as a measure of systematic error and an Uncertainty Area (UA) indicating random error. Analysis showed that mean JND threshold and median UA were both significantly higher in dorsiflexion when compared to plantarflexion (p = 0.008, d = 0.52; p = 0.001, rb= 0.58). These findings indicate that ankle proprioceptive acuity is not uniform for sagittal plane ankle motion but is higher for plantarflexion. We discuss differences in plantar and dorsiflexor muscle mechanoreceptor density and central proprioceptive signal processing as possible reasons for the observed differences in acuity and highlight the importance of understanding movement-specific proprioceptive acuity for designing effective rehabilitation protocols.

Most stroke patients do not use their paretic limb whereas they are able to. The Constraint-Induced Movement Therapy (CIMT) is effective to reverse this non-use behaviour in some patients but is inapplicable or unsuccessful on others. Here, we investigate how much non-use could come from shoulder weakness instead of the behavioural conditioning treated by the CIMT. We asked 26 healthy participants to reach a target while holding a dumbbell. We found that 18/26 participants exhibit proximal arm non-use when loaded and that non-use reduces shoulder torque of final posture. We either found that non-use improves accuracy in a high gravity field. Following optimal control policy, we explain how the non-use could be an adaptative solution when the shoulder is weak. Our results show the need to include muscular strength into cost function used to model human movement. The framework presented here suggests that psychological non-use could be treated effectively with CIMT, while physiological non-use, resulting from shoulder weakness, might respond better to anti-gravity muscles strengthening.

The purpose of this study was to clarify predictive visual patterns of skilled table tennis players during forehand rallies. Collegiate male table tennis players (n = 7) conducted forehand rallies at a constant tempo (100, 120 and 150 bpm) using a metronome. In each tempo condition, participants performed a total of 30 strokes (three conditions). Gaze fixation time, gaze targets and saccade eye movements were detected by video footage of an eye tracking device. We found that participants gazed at a ball approaching them only 20 % of the total rally time. Participants tended to gaze at the ball when the opponent hit the ball and move their gaze away from the ball after that. Furthermore, saccades were directed toward the opposite side of the court including the opponent after tracking the ball. These findings suggest that focusing on the opponent motion is important for successful forehand table tennis rallies. Taken together, skilled table tennis players are likely to use unique visual patterns for interceptive sports players to estimate spatiotemporal information about the ball.