Environment-based approaches to improve participation of young people with physical disabilities during COVID-19.

AIM: To examine the effects of the Pathways and Resources for Engagement and Participation (PREP) intervention during the COVID-19 pandemic on (1) activity performance and satisfaction, and (2) motor, cognitive, and affective body functions. METHOD: An interrupted time-series design with multiple baselines across 21 young people (13 females, eight males) aged 16 to 25 years (median = 21 years 5 months) with physical disabilities was employed. The young people engaged in an 8-week self-chosen leisure activity (e.g. football, piano, photography) at their home or community. The Canadian Occupational Performance Measure (COPM) assessed activity performance and satisfaction weekly. Mental health problems, including affective and cognitive outcomes, were assessed weekly using the Behavior Assessment System for Children, Third Edition. Motor functions (e.g. trunk control, reaching, strength) were assessed biweekly. Linear mixed-effects models were used. RESULTS: The intervention had large effects on activity performance (0.78) and satisfaction (0.88) with clinically significant change in COPM scores (2.6 [95% confidence interval {CI}: 2.0-3.2] and 3.2 points [95% CI: 2.4-3.9] respectively). Young people without mental health problems at baseline benefited more from the intervention (p = 0.028). Improvements in at least one domain of body function occurred in 10 young people especially for motor outcomes. INTERPRETATION: Results demonstrate the effectiveness of PREP during adverse times and suggest benefits going beyond participation, involving outcomes at the body-function level. WHAT THIS PAPER ADDS: Environmental-based interventions can improve participation even during adverse times such as the COVID-19 pandemic. Significant improvement with large effect sizes occurred in both activity performance and satisfaction. Intervention was effective for all; those without mental health problems benefited more. Improvements in body-function outcomes were partially observed, especially in motor-related outcomes. Body functions may improve through participation even if not targeted by the intervention.

Reaction of human walking to transient block of vision: analysis in the context of indirect, referent control of motor actions.

Human locomotion may result from monotonic shifts in the referent position, R, of the body in the environment. R is also the spatial threshold at which muscles can be quiescent but are activated depending on the deflection of the current body configuration Q from R. Shifts in R are presumably accomplished with the participation of proprioceptive and visual feedback and responsible for transferring stable body balance (equilibrium) from one place in the environment to another, resulting in rhythmic activity of multiple muscles by a central pattern generator (CPG). We tested predictions of this two-level control scheme. In particular, in response to a transient block of vision during locomotion, the system can temporarily slow shifts in R. As a result, the phase of rhythmical movements of all four limbs will be changed for some time, even though the rhythm and other characteristics of locomotion will be fully restored after perturbation, a phenomenon called long-lasting phase resetting. Another prediction of the control scheme is that the activity of multiple muscles of each leg can be minimized reciprocally at specific phases of the gait cycle both in the presence and absence of vision. Speed of locomotion is related to the rate of shifts in the referent body position in the environment. Results confirmed that human locomotion is likely guided by feedforward shifts in the referent body location, with subsequent changes in the activity of multiple muscles by the CPG. Neural structures responsible for shifts in the referent body configuration causing locomotion are suggested.

Responsiveness of the Reaching Performance Scale for Stroke.

OBJECTIVE: The objective of the study was to estimate the internal and external responsiveness of the Reaching Performance Scale for Stroke (RPSS) in individuals with stroke. DESIGN: Retrospective analysis of data from 4 randomized controlled trials. SETTING: Recruitment locations spanning rehabilitation centers and hospitals in Canada, Italy, Argentina, Peru, and Thailand. PARTICIPANTS: Data from 567 participants (acute to chronic stroke; N=567) were available. INTERVENTIONS: All 4 studies involved training using virtual reality for upper limb rehabilitation. MAIN OUTCOME MEASURES: RPSS and upper extremity Fugl-Meyer Assessment (FMA-UE) scores. Responsiveness was quantified for all data and across different stages of stroke. Internal responsiveness of the RPSS was quantified as effect-sizes calculated using post and preintervention change data. External responsiveness was quantified using orthogonal regressions between FMA-UE and RPSS scores. The area under the Receiver Operating Characteristic curve (AUC) was quantified based on the ability of RPSS scores to detect change above FMA-UE minimal clinically important different values across different stages of stroke. RESULTS: The RPSS had high internal responsiveness overall and across the acute or subacute and chronic stages of stroke. For external responsiveness, orthogonal regression analyses indicated that change in FMA-UE scores had positive moderate correlations with both RPSS Close and Far Target scores for all data and across the acute or subacute and chronic stages of stroke (0.6

Age-related changes in upper limb coordination in a complex reaching task.

When reaching to targets within arm's reach, intentional trunk motion must be neutralized by compensatory motion of the upper limb (UL). Advanced age has been associated with deterioration in the coordination of multi-joint UL movements. In the current study, we looked to determine if older adults also have difficulties modifying their UL movements (i.e., coordination between the shoulder and elbow joints), during a complex reaching task when trunk motion is manipulated. Two groups of healthy participants were recruited: 18 young (mean age = 24.28 ± 2.89 years old) and 18 older (mean age = 72.11 ± 2.39 years old) adults. Participants reached to a target with their eyes closed, while simultaneously moving the trunk forward. In 40% of trials, the trunk motion was unexpectedly blocked. Participants performed the task with both their dominant and non-dominant arms, and at a preferred and fast speed. All participants were able to coordinate motion at the elbow and shoulder joints in a similar manner and modify this coordination in accordance with motion at the trunk, regardless of the hand used or speed of movement. Specifically, in reaches that involved forward trunk motion (free-trunk trials), all participants demonstrated increased elbow flexion (i.e., less elbow extension) compared to blocked-trunk trials. In contrast, when trunk motion was blocked (blocked-trunk trials), all reaching movements were accompanied by increased shoulder horizontal adduction. While coordination of UL joints was similar across older and young adults, the extent of changes at the elbow and shoulder was smaller and less consistent in older adults compared to young participants, especially when trunk motion was involved. These results suggest that older adults can coordinate their UL movements based on task requirements, but that their performance is not as consistent as young adults.

Feasibility and preliminary efficacy of a combined virtual reality, robotics and electrical stimulation intervention in upper extremity stroke rehabilitation.

BACKGROUND: Approximately 80% of individuals with chronic stroke present with long lasting upper extremity (UE) impairments. We designed the perSonalized UPper Extremity Rehabilitation (SUPER) intervention, which combines robotics, virtual reality activities, and neuromuscular electrical stimulation (NMES). The objectives of our study were to determine the feasibility and the preliminary efficacy of the SUPER intervention in individuals with moderate/severe stroke. METHODS: Stroke participants (n = 28) received a 4-week intervention (3 × per week), tailored to their functional level. The functional integrity of the corticospinal tract was assessed using the Predict Recovery Potential algorithm, involving measurements of motor evoked potentials and manual muscle testing. Those with low potential for hand recovery (shoulder group; n = 18) received a robotic-rehabilitation intervention focusing on elbow and shoulder movements only. Those with a good potential for hand recovery (hand group; n = 10) received EMG-triggered NMES, in addition to robot therapy. The primary outcomes were the Fugl-Meyer UE assessment and the ABILHAND assessment. Secondary outcomes included the Motor Activity Log and the Stroke Impact Scale. RESULTS: Eighteen participants (64%), in either the hand or the shoulder group, showed changes in the Fugl-Meyer UE or in the ABILHAND assessment superior to the minimal clinically important difference. CONCLUSIONS: This indicates that our personalized approach is feasible and may be beneficial in improving UE function in individuals with moderate to severe impairments due to stroke. TRIAL REGISTRATION: ClinicalTrials.gov NCT03903770. Registered 4 April 2019. Registered retrospectively.

Effect of post-stroke spasticity on voluntary movement of the upper limb.

BACKGROUND: Hemiparesis following stroke is often accompanied by spasticity. Spasticity is one factor among the multiple components of the upper motor neuron syndrome that contributes to movement impairment. However, the specific contribution of spasticity is difficult to isolate and quantify. We propose a new method of quantification and evaluation of the impact of spasticity on the quality of movement following stroke. METHODS: Spasticity was assessed using the Tonic Stretch Reflex Threshold (TSRT). TSRT was analyzed in relation to stochastic models of motion to quantify the deviation of the hemiparetic upper limb motion from the normal motion patterns during a reaching task. Specifically, we assessed the impact of spasticity in the elbow flexors on reaching motion patterns using two distinct measures of the 'distance' between pathological and normal movement, (a) the bidirectional Kullback-Liebler divergence (BKLD) and (b) Hellinger's distance (HD). These measures differ in their sensitivity to different confounding variables. Motor impairment was assessed clinically by the Fugl-Meyer assessment scale for the upper extremity (FMA-UE). Forty-two first-event stroke patients in the subacute phase and 13 healthy controls of similar age participated in the study. Elbow motion was analyzed in the context of repeated reach-to-grasp movements towards four differently located targets. Log-BKLD and HD along with movement time, final elbow extension angle, mean elbow velocity, peak elbow velocity, and the number of velocity peaks of the elbow motion were computed. RESULTS: Upper limb kinematics in patients with lower FMA-UE scores (greater impairment) showed greater deviation from normality when the distance between impaired and normal elbow motion was analyzed either with the BKLD or HD measures. The severity of spasticity, reflected by the TSRT, was related to the distance between impaired and normal elbow motion analyzed with either distance measure. Mean elbow velocity differed between targets, however HD was not sensitive to target location. This may point at effects of spasticity on motion quality that go beyond effects on velocity. CONCLUSIONS: The two methods for analyzing pathological movement post-stroke provide new options for studying the relationship between spasticity and movement quality under different spatiotemporal constraints.

Stability of reaching during standing in stroke.

Reaching from standing requires simultaneous adjustments of focal and postural task elements. We investigated the ability of people with stroke to stabilize the endpoint trajectory while maintaining balance during standing reaches. Nineteen stroke and 11 age-equivalent healthy subjects reached toward a target (n = 30 trials) located beyond arm length from standing. Endpoint and center-of-mass (COM) trajectories were analyzed using the uncontrolled manifold (UCM) approach, with segment angles as elemental variables. A synergy index (SI) represented the normalized difference between segment angle combinations, leading to endpoint or COM trajectory stabilization (VUCM) and lack of stabilization (in an orthogonal space; VORT). A higher SI reflects greater stability. In both groups, the endpoint SI (SIEND) decreased in parallel with endpoint velocity and returned close to baseline at the end of the movement. The range of SIEND was significantly greater in stroke (median: 0.87; QR:0.54) compared with healthy subjects (median: 0.58; QR: 0.33; P = 0.009). In both groups, the lowest SIEND occurred at the endpoint peak velocity, whereas the minimal SIEND of the stroke group (median: 0.51; QR:0.41) was lower than the healthy group (median: 0.25; QR: 0.50; P = 0.033). The COM SI (SICOM) remained stable in both groups (~0.8). The maintenance of a high SICOM despite a large reduction of SIEND in stroke subjects suggests that kinematic redundancy was effectively used to stabilize the COM position, but less so for endpoint position stabilization. Both focal and postural task elements should be considered when analyzing whole body reaching deficits in patients with stroke.NEW & NOTEWORTHY Reaching from standing requires simultaneous adjustments of endpoint and center-of-mass (COM) positions. We used uncontrolled manifold analysis to investigate the impact of stroke on the ability to use kinematic redundancy in this task. Our results showed that COM position was stabilized, whereas endpoint trajectory was more variable in stroke than healthy subjects. Enhancing the capacity to meet multiple task goals may be beneficial for motor recovery after stroke.

Improving body functions through participation in community activities among young people with physical disabilities.

AIM: To examine the impact of engagement in a self-chosen community-based activity on three relevant body functions (motor, cognitive, and affective) as well as on the performance of the selected activity. METHOD: An individual-based interrupted time series design with multiple baselines was used. Seven young people (four males, three females) aged 15 to 25 years (median 18y; interquartile range 17-20y) with physical disabilities participated in an 8-week community activity of choice (e.g. swimming, playing piano). Change in three relevant body functions, underpinning the specific chosen activity, including motor (e.g. Functional Reach Test, Trunk Impairment Scale, dynamometers), cognitive and affective (Behavior Assessment System for Children), as well as activity performance (Canadian Occupational Performance Measure) were measured repeatedly, providing individual outcome trajectories. Linear and mixed-effects models were used. RESULTS: Significant improvements in at least one aspect of motor function (6 out of 6), cognition (3 out of 3), affect (5 out of 7), and performance (7 out of 7) were observed. Specifically, the intervention had a moderate to large effect on hyperactivity (1.45, 95% confidence interval [CI] 1.0-1.9) with a smaller effect on anxiety (0.21, 95% CI 0.10-0.32) and inadequacy (0.21, 95% CI 0.02-0.39). Concurrently, a notable effect size for activity performance (4.61, 95% CI 0.76-8.46) was observed. Average change across motor outcomes was substantial (3.7 SDs from baseline), yet non-significant. INTERPERTATION: Findings provide initial evidence of the benefits resulting from participation-based interventions, emphasizing the merit of meaningful 'real-life' young people-engaging therapy. WHAT THIS PAPER ADDS: Participation-based interventions can impact body-function level outcomes. Significant improvements in the performance of chosen activities were observed. Significant improvements were also seen in cognitive and affective body functions. Improvements in motor-related outcomes were substantial but not statistically significant.

Development of vertical and forward jumping skills in typically developing children in the context of referent control of motor actions.

The empirically based referent control theory of motor actions provides a new framework for understanding locomotor maturation. Mature movement patterns of referent control are characterized by periods of minimization of activity across multiple muscles (global electromyographic [EMG] minima) resulting from transient matching between actual and referent body configurations. We identified whether locomotor maturation in young children was associated with (a) development of referent control and (b) children's frequency of participation in everyday activities evaluated by parents. Kinematics and EMG activity were recorded from typically developing children (n = 15, 3-5 years) and young adults (n = 10, 18-25 years) while walking, vertical or forward jumping. Presence and location of global EMG minima in movement cycles, slopes of ankle vertical/sagittal displacements, and shoulder displacement ratios were evaluated. Children had fewer global EMG minima compared to adults during specific phases of vertical and forward jumps. Ankle displacement profiles for walking and jumping forward were related to each other in adults, whereas those for walking and vertical jumping were related in children. Higher frequency of participation was significantly correlated with more mature jumping patterns in children. A decrease in the number of global EMG minima and changes in ankle movement patterns could be indicators of locomotor immaturity in typically developing children.

Age differences in arm-trunk coordination during trunk-assisted reaching.

Reaching for an object is a basic motor skill that requires precise coordination between elbow, shoulder and trunk motion. The purpose of this research study was to examine age-related differences in compensatory arm-trunk coordination during trunk-assisted reaching. To engage the arm and trunk, an older and younger group of participants were asked to (1) maintain a fixed hand position while flexing forward at the trunk [stationary hand task (SHT)] and (2) reach to a within-arm's reach target while simultaneously flexing forward at the trunk [reaching hand task (RHT)] (Raptis et al. in J Neurophysiol 97:4069-4078, 2007; Sibindi et al. in J Vestib Res 23:237-247, 2013). Both tasks were completed with eyes closed. Participants completed the two tasks with their dominant and non-dominant arms, and at both a fast and a preferred speed. On average, young and older participants performed in a similar manner in the SHT, such that they maintained their hand position by compensating for trunk movement with modifications of the elbow and shoulder joints. In the RHT, young and older participants had similar endpoint accuracy. This similarity in performance between young and older participants in the SHT and RHT tasks was observed regardless of the arm used or movement speed. However, for both tasks, movements in older adults were significantly more variable compared to younger adults as shown by the larger variability in arm-trunk coordination performance (gain scores) in the SHT and higher movement time variability in the RHT. Thus, results imply that older adults maintain their ability to coordinate arm and trunk movements efficiently during reaching actions but are not as consistent as younger adults.

Referent control of anticipatory grip force during reaching in stroke: an experimental and modeling study.

To evaluate normal and impaired control of anticipatory grip force (GF) modulation, we compared GF production during horizontal arm movements in healthy and post-stroke subjects, and, based on a physiologically feasible dynamic model, determined referent control variables underlying the GF-arm motion coordination in each group. 63% of 13 healthy and 48% of 13 stroke subjects produced low sustained initial force (< 10 N) and increased GF prior to arm movement. Movement-related GF increases were higher during fast compared to self-paced arm extension movements only in the healthy group. Differences in the patterns of anticipatory GF increases before the arm movement onset between groups occurred during fast extension arm movement only. In the stroke group, longer delays between the onset of GF change and elbow motion were related to clinical upper limb deficits. Simulations showed that GFs could emerge from the difference between the actual and the referent hand aperture (Ra) specified by the CNS. Similarly, arm movement could result from changes in the referent elbow position (Re) and could be affected by the co-activation (C) command. A subgroup of stroke subjects, who increased GF before arm movement, could specify different patterns of the referent variables while reproducing the healthy typical pattern of GF-arm coordination. Stroke subjects, who increased GF after arm movement onset, also used different referent strategies than controls. Thus, altered anticipatory GF behavior in stroke subjects may be explained by deficits in referent control.

Vestibular and corticospinal control of human body orientation in the gravitational field.

Body orientation with respect to the direction of gravity changes when we lean forward from upright standing. We tested the hypothesis that during upright standing, the nervous system specifies the referent body orientation that defines spatial thresholds for activation of multiple muscles across the body. To intentionally lean the body forward, the system is postulated to transfer balance and stability to the leaned position by monotonically tilting the referent orientation, thus increasing the activation thresholds of ankle extensors and decreasing their activity. Consequently, the unbalanced gravitational torque would start to lean the body forward. With restretching, ankle extensors would be reactivated and generate increasing electromyographic (EMG) activity until the enhanced gravitational torque would be balanced at a new posture. As predicted, vestibular influences on motoneurons of ankle extensors evaluated by galvanic vestibular stimulation were smaller in the leaned compared with the upright position, despite higher tonic EMG activity. Defacilitation of vestibular influences was also observed during forward leaning when the EMG levels in the upright and leaned position were equalized by compensating the gravitational torque with a load. The vestibular system is involved in the active control of body orientation without directly specifying the motor outcome. Corticospinal influences originating from the primary motor cortex evaluated by transcranial magnetic stimulation remained similar at the two body postures. Thus, in contrast to the vestibular system, the corticospinal system maintains a similar descending facilitation of motoneurons of leg muscles at different body orientations. The study advances the understanding of how body orientation is controlled. NEW & NOTEWORTHY The brain changes the referent body orientation with respect to gravity to lean the body forward. Physiologically, this is achieved by shifts in spatial thresholds for activation of ankle muscles, which involves the vestibular system. Results advance the understanding of how the brain controls body orientation in the gravitational field. The study also extends previous evidence of empirical control of motor function, i.e., without the reliance on model-based computations and direct specification of motor outcome.

Spasticity may obscure motor learning ability after stroke.

Previous motor learning studies based on adapting movements of the hemiparetic arm in stroke subjects have not accounted for spasticity occurring in specific joint ranges (spasticity zones), resulting in equivocal conclusions about learning capacity. We compared the ability of participants with stroke to rapidly adapt elbow extension movements to changing external load conditions outside and inside spasticity zones. Participants with stroke ( n = 12, aged 57.8 ± 9.6 yr) and healthy age-matched controls ( n = 8, 63.5 ± 9.1 yr) made rapid 40°-50° horizontal elbow extension movements from an initial (3°) to a final (6°) target. Sixteen blocks (6-10 trials/block) consisting of alternating loaded (30% maximal voluntary contraction) and nonloaded trials were made in one (controls) or two sessions (stroke; 1 wk apart). For the stroke group, the tonic stretch reflex threshold angle at which elbow flexors began to be activated during passive elbow extension was used to identify the beginning of the spasticity zone. The task was repeated in joint ranges that did or did not include the spasticity zone. Error correction strategies were identified by the angular positions before correction and compared between groups and sessions. Changes in load condition from no load to load and vice versa resulted in undershoot and overshoot errors, respectively. Stroke subjects corrected errors in 1-4 trials compared with 1-2 trials in controls. When movements did not include the spasticity zone, there was an immediate decrease in the number of trials needed to restore accuracy, suggesting that the capacity to learn may be preserved after stroke but masked by the presence of spasticity. NEW & NOTEWORTHY When arm movements were made outside, instead of inside, the range affected by spasticity, there was an immediate decrease in the number of trials needed to restore accuracy in response to a change in the external load. This suggests that motor learning processes may be preserved in patients with stroke but masked by the presence of spasticity in specific joint ranges. This has important implications for designing rehabilitation interventions predicated on motor learning principles.

Referent control of the orientation of posture and movement in the gravitational field.

This study addresses the question of how posture and movement are oriented with respect to the direction of gravity. It is suggested that neural control levels coordinate spatial thresholds at which multiple muscles begin to be activated to specify a referent body orientation (RO) at which muscle activity is minimized. Under the influence of gravity, the body is deflected from the RO to an actual orientation (AO) until the emerging muscle activity and forces begin to balance gravitational forces and maintain body stability. We assumed that (1) during quiet standing on differently tilted surfaces, the same RO and thus AO can be maintained by adjusting activation thresholds of ankle muscles according to the surface tilt angle; (2) intentional forward body leaning results from monotonic ramp-and-hold shifts in the RO; (3) rhythmic oscillation of the RO about the ankle joints during standing results in body swaying. At certain sway phases, the AO and RO may transiently overlap, resulting in minima in the activity of multiple muscles across the body. EMG kinematic patterns of the 3 tasks were recorded and explained based on the RO concept that implies that these patterns emerge due to referent control without being pre-programmed. We also confirmed the predicted occurrence of minima in the activity of multiple muscles at specific body configurations during swaying. Results re-affirm previous rejections of model-based computational theories of motor control. The role of different descending systems in the referent control of posture and movement in the gravitational field is considered.

Validation of reaching in a virtual environment in typically developing children and children with mild unilateral cerebral palsy.

AIM: To compare three reaching movements made in two planes between a low-cost, game-based virtual reality and a matched physical environment in typically developing children and children with cerebral palsy (CP). To determine if differences in kinematics are related to sensory deficits. METHOD: An observational study in which 27 children (typically developing, n=17, mean age 13y, [SD] 2y 2mo, range 9y 3mo-17y 2mo; CP, n=10, mean age 13y 8mo, [SD] 1y 8mo, range 11y 1mo-17y 1mo, Manual Ability Classification System levels I-II) performed 15 trials of three gestures in each of a virtual reality and a matched physical environment. Upper-limb and trunk kinematics were recorded using an electromagnetic system (G4, Polhemus, six markers, 120Hz). RESULTS: Compared to the physical environment, movements in virtual reality made by typically developing children were slower (p=0.002), and involved less trunk flexion (p=0.002) and rotation (p=0.026). Children with CP had more curved trajectories (p=0.005) and used less trunk flexion (p=0.003) and rotation (p=0.005). Elbow and shoulder kinematics differed from 2.8% to 155.4% between environments in both groups. Between groups, there were small, clinically insignificant differences with only the vertical gesture being longer in typically developing children. Children with CP who had greater tactile impairment used more trunk displacement. INTERPRETATION: Clinicians and researchers need to be aware of differences in movement variables when setting goals or designing protocols for improving reaching in children with CP using low-cost, game-based virtual reality systems. WHAT THIS PAPER ADDS: Upper-limb kinematics differed in each group when reaching in physical versus virtual environments. There were small differences in movements made by children with mild unilateral cerebral palsy (CP) compared to typically developing children. Differences in reaching kinematics should be considered when goal setting using virtual reality interventions for children with mild unilateral CP.

Active Video Gaming for Children with Cerebral Palsy: Does a Clinic-Based Virtual Reality Component Offer an Additive Benefit? A Pilot Study.

AIMS: To compare changes in gross motor skills and functional mobility between ambulatory children with cerebral palsy who underwent a 1-week clinic-based virtual reality intervention (VR) followed by a 6-week, therapist-monitored home active video gaming (AVG) program and children who completed only the 6-week home AVG program. METHODS: Pilot non-randomized controlled trial. Five children received 1 hour of VR training for 5 days followed by a 6-week home AVG program, supervised online by a physical therapist. Six children completed only the 6-week home AVG program. The Gross Motor Function Measure Challenge Module (GMFM-CM) and Six Minute Walk Test (6MWT) evaluated change. RESULTS: There were no significant differences between groups. The home AVG-only group demonstrated a statistically and clinically significant improvement in GMFM-CM scores following the 6-week AVG intervention (median difference 4.5 points, interquartile range [IQR] 4.75, p = 0.042). The VR + AVG group demonstrated a statistically and clinically significant decrease in 6MWT distance following the intervention (median decrease 68.2 m, IQR 39.7 m, p = 0.043). All 6MWT scores returned to baseline at 2 months post-intervention. CONCLUSION: Neither intervention improved outcomes in this small sample. Online mechanisms to support therapist-child communication for exercise progression were insufficient to individualize exercise challenge.

Referent control and motor equivalence of reaching from standing.

Motor actions may result from central changes in the referent body configuration, defined as the body posture at which muscles begin to be activated or deactivated. The actual body configuration deviates from the referent configuration, particularly because of body inertia and environmental forces. Within these constraints, the system tends to minimize the difference between these configurations. For pointing movement, this strategy can be expressed as the tendency to minimize the difference between the referent trajectory (RT) and actual trajectory (QT) of the effector (hand). This process may underlie motor equivalent behavior that maintains the pointing trajectory regardless of the number of body segments involved. We tested the hypothesis that the minimization process is used to produce pointing in standing subjects. With eyes closed, 10 subjects reached from a standing position to a remembered target located beyond arm length. In randomly chosen trials, hip flexion was unexpectedly prevented, forcing subjects to take a step during pointing to prevent falling. The task was repeated when subjects were instructed to intentionally take a step during pointing. In most cases, reaching accuracy and trajectory curvature were preserved due to adaptive condition-specific changes in interjoint coordination. Results suggest that referent control and the minimization process associated with it may underlie motor equivalence in pointing. NEW & NOTEWORTHY: Motor actions may result from minimization of the deflection of the actual body configuration from the centrally specified referent body configuration, in the limits of neuromuscular and environmental constraints. The minimization process may maintain reaching trajectory and accuracy regardless of the number of body segments involved (motor equivalence), as confirmed in this study of reaching from standing in young healthy individuals. Results suggest that the referent control process may underlie motor equivalence in reaching.

Perceptuo-motor planning during functional reaching after stroke.

In healthy young adults, reaching movements are planned such that the initial grasp position on the object is modulated based on the final task goal. This perceptuo-motor coupling has been described as the end-state comfort effect. This study aimed to determine the extent to which visuo-perceptual and motor deficits, but not neglect, due to stroke impact end-state comfort measured as the grasp-height effect. Thirty-four older adults (17 controls, 17 chronic stroke) performed a functional goal-directed two-sequence task with each arm, consisting of reaching and moving a cylindrical object (drain plunger) from an initial to four target platform heights, standardized to body height, in a block randomized sequence. Arm motor impairment (Fugl-Meyer Assessment) and visual-perceptual deficits (Motor-Free Visual Perception Test) were assessed in stroke subjects, and arm and trunk kinematics were assessed in all subjects. The primary outcome measure of the grasp-height effect was the relationship between the grasp heights used at the home position and the final target platform heights. Mixed model analysis was used for data analysis. The grasp-height effect was present in all participants, but decreased in stroke subjects with visuo-perceptual impairments compared to controls. In stroke subjects with sensorimotor impairments alone, indicated by altered kinematics, the grasp-height effect was comparable to controls. This first study examining the grasp-height effect in individuals with stroke provides new knowledge of the impact of visuo-perceptual deficits on movement planning and execution, which may assist clinicians in selecting more effective treatment strategies to improve perceptuo-motor skills and enhance motor recovery.

The added value of kinematic evaluation of the timed finger-to-nose test in persons post-stroke.

BACKGROUND: Upper limb coordination in persons post-stroke may be estimated by the commonly used Finger-to-Nose Test (FNT), which is also part of the Fugl-Meyer Assessment. The total movement time (TMT) is used as a clinical outcome measure, while kinematic evaluation also enables an objective quantification of movement quality and motor performance. Our aims were to kinematically characterize FNT performance in persons post-stroke and controls and to investigate the construct validity of the test in persons with varying levels of impairment post-stroke. METHODS: A three-dimensional motion capture system recorded body movements during performance of the FNT in 33 persons post-stroke who had mild or moderate upper limb motor impairments (Fugl-Meyer scores of 50-62 or 32-49, respectively), and 41 non-disabled controls. TMT and kinematic variables of the hand (pointing time, peak speed, time to peak speed, number of movement units, path ratio, and pointing accuracy), elbow/shoulder joints (range of motion, interjoint coordination), and scapular/trunk movement were calculated. Our analysis focused on the pointing phase (knee to nose movement of the FNT). Independent t or Mann-Whitney U tests and effect sizes were used to analyze group differences. Sub-group analyses based on movement time and stroke severity were performed. Within the stroke group, simple and multiple linear regression were used to identify relationships between TMT to kinematic variables. RESULTS: The stroke group had significant slower TMT (mean difference 2.6 s, d = 1.33) than the control group, and six other kinematic variables showed significant group differences. At matched speeds, the stroke group had lower accuracy and excessive scapular and trunk movements compared to controls. Pointing time and elbow flexion during the pointing phase were most related to stroke severity. For the stroke group, the number of movement units during the pointing phase showed the strongest association with the TMT, and explained 60% of the TMT variance. CONCLUSIONS: The timed FNT discriminates between persons with mild and moderate upper limb impairments. However, kinematic analysis to address construct validity highlights differences in pointing movement post-stroke that are not captured in the timed FNT.