Tal Krasovsky

Review: Toward a Better Understanding of Coordination in Healthy and Poststroke Gait:

Locomotor coordination characterizes healthy gait and rehabilitation effectiveness in poststroke individuals. However, despite a large number of clinic-based and laboratory-based measurement options, to date there is no gold standard for measurement of locomotor coordination. A lack of a common definition for locomotor coordination may be a cause of this confusion. Coordination during gait includes both spatial and temporal components that may be measured in extrinsic or intrinsic reference frames. Measurement tools have been used to evaluate one or both aspects of coordination. The authors suggest an operational definition of locomotor coordination and describe how current measures in healthy and poststroke individuals fit with this definition. They define locomotor coordination as an ability to maintain a context-dependent and phase-dependent cyclical relationship between different body segments or joints in both spatial and temporal domains. Advantages and disadvantages of laboratory-based measures, such as cyclograms, discrete and continuous relative phase, power spectral density, and others are summarized and discussed. In addition to the definition, the authors propose a clinically feasible measurement paradigm that accentuates the adaptive component of coordination and that may be useful in merging the clinical and laboratory-based approaches to locomotor coordination.

Stability of gait and interlimb coordination in older adults

Most falls in older adults occur when walking, specifically following a trip. This study investigated the short- and longer term responses of young (n = 24, 27.6 ± 4.5 yr) and older adults (n = 18, 69.1 ± 4.2 yr) to a trip during gait at comfortable speed and the role of interlimb coordination in recovery from tripping. Subjects walked on a self-paced treadmill when forward movement of their dominant leg was unexpectedly arrested for 250 ms. Recovery of center of mass (COM) movements and of double-support duration following perturbation was determined. In addition, the disruption and recovery of interlimb coordination of the arms and legs was evaluated. Although young and older subjects used similar lower limb strategies in response to the trip, older adults had less stable COM movement patterns before perturbation, had longer transient destabilization (>25%) after perturbation, required more gait cycles to recover double-support duration (older, 3.48 ± 0.7 cycles; young, 2.88 ± 0.4 cycles), and had larger phase shifts that persisted after perturbation (older, -83° to -90°; young, -39° to -42°). Older adults also had larger disruptions to interlimb coordination of the arms and legs. The timing of the initial disruption in coordination was correlated with the disturbance in gait stability only in young adults. In older adults, greater initial COM instability was related to greater longer term arm incoordination. These results suggest a relationship between interlimb coordination and gait stability, which may be associated with fall risk in older adults. Reduced coordination and gait stability suggest a need for stability-related functional training even in high-functioning older adults.

Changes in the referent body location and configuration may underlie human gait, as confirmed by findings of multi-muscle activity minimizations and phase resetting

Locomotion is presumably guided by feed-forward shifts in the referent body location in the desired direction in the environment. We propose that the difference between the actual and the referent body locations is transmitted to neurons that virtually diminish this difference by appropriately changing the referent body configuration, i.e. the body posture at which muscles reach their recruitment thresholds. Muscles are activated depending on the gap between the actual and the referent body configurations resulting in a step being made to minimize this gap. This hypothesis implies that the actual and the referent leg configurations can match each other at certain phases of the gait cycle, resulting in minimization of leg muscle activity. We found several leg configurations at which EMG minima occurred, both during forward and backward gait. It was also found that the set of limb configurations associated with EMG minima can be changed by modifying the pattern of forward and backward gait. Our hypothesis predicts that, in response to perturbations of gait, the rate of shifts in the referent body location can temporarily be changed to avoid falling. The rate influences the phase of rhythmic limb movements during gait. Therefore, following the change in the rate of the referent body location, the whole gait pattern, for all four limbs, will irreversibly be shifted in time (long-lasting and global phase resetting) with only transient changes in the gait speed, swing and stance timing and cycle duration. Aside from transient changes in the duration of the swing and/or stance phase in response to perturbation, few previous studies have documented long-lasting and global phase resetting of human gait in response to perturbation. Such resetting was a robust finding in our study. By confirming the notion that feed-forward changes in the referent body location and configuration underlie human locomotion, this study solves the classical problem in the relationship between stability of posture and gait and advances the understanding of how human locomotion involves the whole body and is accomplished in a spatial frame of reference associated with the environment.

Deficits in intersegmental trunk coordination during walking are related to clinical balance and gait function in chronic stroke.

Background and Purpose: Decreased walking speed after stroke may be related to changes in temporal and distance gait factors, endurance, and balance. Functional gait deficits may also be related to changes in coordination, specifically between transverse (yaw) plane trunk movements. Our aim was to determine the relationship between intersegmental coordination during gait and functional gait and balance deficits in individuals with stroke. Methods: Eleven individuals with chronic stroke and 11 age-matched subjects without disability participated in 2 sessions. In Session 1, clinical evaluations of trunk/limb impairment (Chedoke-McMaster Stroke Assessment), functional gait (Functional Gait Assessment), and balance (BesTest) were performed. In Session 2, gait kinematics during eight 30-second walking trials on a self-paced treadmill at 2 speeds (comfortable and equivalent) were recorded. Equivalence of walking speeds was obtained by asking subjects without disability to walk approximately 20% slower and subjects with stroke to walk approximately 20% faster than their comfortable speed. Thorax and pelvis 3-dimensional angular ranges of motion (ROMs) and intersegmental coordination using the continuous relative phase were analyzed. Results: Comfortable walking speed was slower in subjects with stroke (0.78 m/s) than in subjects without disability (1.22 m/s), despite matched cadences. At both comfortable and equivalent walking speeds (0.97–0.98 m/s), participants with stroke used more thoracic ROM than pelvic transverse ROM in comparison with subjects without disability. Transverse thorax-pelvis coordination was similar between groups when walking speeds were equivalent, but there was more in-phase coordination in participants with stroke walking at their comfortable, slower speed. In subjects with stroke, thoracic ROM and continuous relative phase were correlated with several clinical functional gait and balance measures. Discussion and Conclusion: Changes in segmental transverse ROM and coordination were associated with poor gait and with balance abilities in individuals with stroke. Interventions focusing on recovery of these movement characteristics may lead to better clinical outcomes.

Reduced gait stability in high-functioning poststroke individuals

Falls during walking are a major cause of poststroke injury, and walking faster may decrease the ability to recover following a gait perturbation. We compared gait stability between high-functioning poststroke individuals and controls and evaluated the effect of gait speed on gait stability. Ten stroke subjects and ten age-matched controls walked on a self-paced treadmill at two speeds (matched/faster). Movement of the nonparetic/dominant leg was arrested unexpectedly at early swing. Poststroke individuals lowered the perturbed leg following perturbation (58% of cases) while controls maintained the leg elevated (49% of cases; P < 0.01). In poststroke individuals, double-support duration was restored later than in controls (4.6 ± 0.8 vs. 3.2 ± 0.3 strides; P < 0.007), and long-term phase shifts of arm and leg movements were larger and less coordinated on the paretic side. A moderate speed increase (~20%) enhanced the incidence of leg lowering in controls but not in stroke subjects. Faster walkers in both groups had a more coordinated response, limited to the nonparetic side in the stroke group. However, faster walkers were not more stable following perturbation. Our results suggest that gait perturbations can target basic control processes and identify neurological locomotor deficits in individuals with fall risk. Central regulation of body translation in space is involved in recovery of steady-state walking. Impaired descending control (stroke) decreases the ability of the motor system to recover from perturbations and regulate interlimb phase relationships, especially when changing gait speed. However, interlimb coordination may not be a major factor in the recovery of gait stability.

Effects of walking speed on gait stability and interlimb coordination in younger and older adults

Many falls in older adults occur during walking following trips. Following a trip, older adults take longer than younger adults to recover steady-state walking. Although faster gait speed may improve interlimb coordination, it may also increase fall risk in older adults. We hypothesized that older adults would take longer than younger adults to recover from an unexpected perturbation during gait especially when walking faster. Twelve younger (26.3 ± 4.4 years) and 12 older adults (68.5 ± 3.4 years) walked at comfortable, faster and slower speeds when movement of the dominant leg was unexpectedly arrested for 250 ms at 20% swing length. Gait stability was evaluated using the short- and longer-term response to perturbation. In both groups, walking faster diminished the occurrence of elevation and increased that of leg lowering. Older adults took longer than younger adults to recover steady-state walking at all speeds (3.36 ± 0.11 vs. 2.89 ± 0.08 strides) but longer-term recovery of gait stability was not related to gait speed. Arm-leg and inter-arm coordination improved with increasing gait speed in both groups, but older adults had weaker inter-leg coupling following perturbation at all speeds. Although both younger and older adults used speed appropriate responses immediately following perturbation, longer duration of recovery of steady-state walking in older adults may increase fall risk in uncontrolled situations, regardless of gait speed. Recovery from perturbation when walking faster was associated with better interlimb coordination, but not with better gait stability. This indicates that interlimb coordination and gait stability may be distinct features of locomotion.

Development and validation of tele-health system for stroke rehabilitation

Abstract Tele-rehabilitation refers to the use of information and communication technologies to provide rehabilitation services to people in their homes or other environments. The objective of this paper was to present the development, validation, and usability testing of a low-cost, markerless, full-body tracking virtual reality system designed to provide remote rehabilitation of the upper extremity in patients with stroke. The Methods and Results sections present the progress of our work on system development, system validations, and a feasibility/usability study. We conclude with a brief summary of the initial stages of an intervention study and a discussion of our findings in the context of the next steps. The validation study demonstrated considerable accuracy for some outcomes (i.e., shoulder “pitch” angle, elbow flexion, trunk forward, and side-to-side deviation). In addition, positive responses were received from the clients who participated in the feasibility study. We are currently in the process of improving the accuracy of the system and analyzing results from a randomized clinical trial, which assessed the effectiveness of the system to improve upper extremity function post-stroke.

Arm-trunk coordination as a measure of vestibulospinal efficiency.

When arm and trunk segments are involved in reaching for objects within arms reach, vestibulospinal pathways compensate for trunk motion influence on arm movement. This compensatory arm-trunk synergy is characterised by a gain coefficient of 0 to 1. Vestibular patients have less efficient arm-trunk synergies and lower gains. To assess the clinical usefulness of the gain measure, we used a portable ultrasound-based device to characterize arm-trunk coordination deficits in vestibular patients. Arm-trunk coordination without vision was measured in a Stationary Hand Task where hand position was maintained during trunk movement, and a Reaching Task with and without trunk motion. Twenty unilateral vestibular patients and 16 controls participated. For the Stationary Hand task, patient gains ranged from g=0.94 (good compensation) to 0.31 (poor compensation) and, on average, were lower than in controls (patients: 0.67 ± 0.19; controls: 0.85 ± 0.07; p< 0.01). Gains were significantly correlated with clinical tests (Sensory Organization; r=0.62, p< 0.01, Foam Romberg Eyes Closed; r=0.65, p< 0.01). For the Reaching Task, blocking trunk movement during reaching modified hand position significantly more in patients (8.2 ± 4.3 cm) compared to controls (4.5 ± 1.7 cm, p< 0.02) and the amount of hand position deviation was correlated with the degree of vestibular loss in a sub-group (n=14) of patients. Measurement of the Stationary Task arm-trunk gain and hand deviations during the Reaching Task can help characterize sensorimotor problems in vestibular-deficient patients and track recovery following therapeutic interventions. The ultrasound-based portable device is suitable for measuring vestibulospinal deficits in arm-trunk coordination in a clinical setting.

Kinematic features of continuous hand reaching movements under simple and complex rhythmical constraints.

BACKGROUND Auditory cues are known to alter movement kinematics in healthy people as well as in people with neurological conditions (e.g., Parkinsons disease or stroke). Pacing movement to rhythmical constraints is known to change both the spatial and temporal features of movement. However, the effect of complexity of pacing on the spatial and temporal kinematic properties is still poorly understood. The current study investigated spatial and temporal aspects of movement (path and speed, respectively) and their integration while subjects followed simple isochronous or complex non-isochronous rhythmical constraints. Spatiotemporal decoupling was expected under the latter constraint. METHODS Ten subjects performed point-to-point hand movements towards visual targets on the surface of a hemisphere, while following continuous auditory cues of different pace and meter. The spatial and temporal properties of movement were compared to geodesic paths and unimodal bell-shaped speed profiles, respectively. Multiple two-way RM-ANOVAs (pace [1-2 Hz] x meter [duple-triple]) were performed on the different kinematic variables calculated to assess hand deviations from the model data (p< or = 0.05). RESULTS As expected, increasing pace resulted in straighter hand paths and smoother speed profiles. Meter, however, affected only the path (shorter and straighter under triple) without significantly changing speed. Such an effect was observed at the slow pace only. CONCLUSIONS Under simple rhythmic cues, an increase in pace causes spontaneous adjustments in spatial features (straighter hand paths) while preserving temporal ones (maximally-smoothed hand speeds). Complex rhythmical cues in contrast perturb spatiotemporal coupling and challenge movement control. These results may have important practical implications in motor rehabilitation.