W. Zev Rymer

Robot-assisted reaching exercise promotes arm movement recovery in chronic hemiparetic stroke: a randomized controlled pilot study.

Background and purposeProviding active assistance to complete desired arm movements is a common technique in upper extremity rehabilitation after stroke. Such active assistance may improve recovery by affecting somatosensory input, motor planning, spasticity or soft tissue properties, but it is labor intensive and has not been validated in controlled trials. The purpose of this study was to investigate the effects of robotically administered active-assistive exercise and compare those with free reaching voluntary exercise in improving arm movement ability after chronic stroke.MethodsNineteen individuals at least one year post-stroke were randomized into one of two groups. One group performed 24 sessions of active-assistive reaching exercise with a simple robotic device, while a second group performed a task-matched amount of unassisted reaching. The main outcome measures were range and speed of supported arm movement, range, straightness and smoothness of unsupported reaching, and the Rancho Los Amigos Functional Test of Upper Extremity Function.Results and discussionThere were significant improvements with training for range of motion and velocity of supported reaching, straightness of unsupported reaching, and functional movement ability. These improvements were not significantly different between the two training groups. The group that performed unassisted reaching exercise improved the smoothness of their reaching movements more than the robot-assisted group.ConclusionImprovements with both forms of exercise confirmed that repeated, task-related voluntary activation of the damaged motor system is a key stimulus to motor recovery following chronic stroke. Robotically assisting in reaching successfully improved arm movement ability, although it did not provide any detectable, additional value beyond the movement practice that occurred concurrently with it. The inability to detect any additional value of robot-assisted reaching may have been due to this pilot studys limited sample size, the specific diagnoses of the participants, or the inclusion of only individuals with chronic stroke.

Objective quantification of spastic hypertonia: correlation with clinical findings.

To develop a reliable and objective technique for quantifying spastic hypertonia, ten chronically hemiplegic patients with varying degrees of spasticity were studied on three occasions during several weeks. The modified Ashworth scale, a clinical assessment of extremity tone, was performed before and after each of the following objective tests: (1) torque and EMG measurements during ramp and hold angular displacement about the elbow, (2) pendulum test of the lower extremity, and (3) H/M ratio studies of upper and lower extremities. Subject motor function was also quantified using the Fugl-Meyer motor assessment scale. A regression analysis was performed to determine how successfully each of the objective measures correlated with the clinical yardstick, the modified Ashworth scale. A similar correlation between the objective measures and the Fugl-Meyer motor assessment scale was performed. Temporal reproducibility of a test for a given subject was evaluated by performing an ANOVA of repeated measures for each test over the three study sessions in a given subject. We conclude that (1) both the ramp and hold threshold measurements and pendulum test offer acceptable objective measures of spastic hypertonia since they correlate closely with clinical perception, (2) the Fugl-Meyer motor assessment scale also correlates closely with the severity of spastic tone, and (3) objective measures of spastic hypertonia are often surprisingly reproducible when repeatedly applied to a selected group of chronic hemiplegic patients with long-standing spasticity.

Deficits in the coordination of multijoint arm movements in patients with hemiparesis: evidence for disturbed control of limb dynamics.

Abstract. This study provides a detailed analysis of disturbances in the kinematics and dynamics of the acceleration phase of multijoint arm movements in six patients with chronic hemiparesis. Movements of the dominant and nondominant limbs were also examined in three control subjects. Subjects performed rapid movements from a central starting point to 16 targets located equidistantly around the circumference of a circle. Support of the upper limb was provided by an air-bearing apparatus, which allowed very low friction movements in the horizontal plane. We found that patients retained the capacity to modulate, in response to target direction, the initial direction of movements performed with the paretic limb. However, in comparison to the nonparetic limb or control subjects, movements of the paretic limb were misdirected systematically. An inverse dynamics analysis revealed an abnormal spatial tuning of the muscle torque at the elbow used to initiate movements of the paretic limb. Based on electromyographic recordings, similar spatial abnormalities were also apparent in the initial activations of elbow muscles. We argue that these spatial abnormalities result from a systematic disturbance in the control signal to limb muscles that cannot be attributed to previously identified mechanisms such as weakness, spasticity mediated restraint, or stereotypic muscle activation patterns (muscle synergies). Instead, our analysis of movement dynamics and simulation studies demonstrate that the spatial abnormalities are consistent with an impaired feedforward control of the passive interaction torques which arise during multijoint movements. This impaired control is hypothesized to reflect a degradation of the internal representation of limb dynamics that occurs either as a primary consequence of brain injury or secondary to disuse.

Target-dependent differences between free and constrained arm movements in chronic hemiparesis

This study compares the kinematic and kinetic characteristics of constrained and free upper limb movements in eight subjects with chronic hemiparesis. Movements of the dominant and nondominant limbs were also examined in five control subjects. Rapid movements were performed in the horizontal plane from a central starting point to five targets located to require various combinations of flexion/extension rotations at the elbow and shoulder. Support of the upper limb against gravity loading was provided either by a low-friction air-bearing apparatus (constrained condition) or by voluntary generation of abduction and external rotation torques at the shoulder (free condition). Data analysis focused on the peak joint torques generated during the acceleratory phase of movement, and on the net change in joint angles at the elbow and shoulder. We found that movement parameters were broadly invariant with support condition for either limb of control subjects, as well as for the nonparetic limb of hemiparetic subjects. In contrast, support condition had a target-dependent effect on movements of the paretic limb. Relative to the constrained condition, peak torques for free arm movements were significantly reduced for distal targets requiring elbow extension and/or shoulder flexion torques. However, peak elbow flexion and shoulder extension joint torques for proximal targets were relatively unaffected by support condition. Of perhaps more functional importance, free movements were characterized by a target-dependent restriction in the hand’s work area that reflected a reduced range of active elbow extension, relative to constrained movements. The target-dependent effects of support condition on movements of the paretic limb are consistent with the existence of abnormal constraints on muscle activation patterns in subjects with chronic hemiparesis, namely an abnormal linkage between activation of the elbow flexors and shoulder extensors, abductors, and external rotators.

Estimation of muscle forces about the wrist joint during isometric tasks using an EMG coefficient method

A technique for estimating isometric muscle forces based on EMGs and anatomical parameters is presented. In the present study, we record EMGs from five muscles acting at the wrist, during a series of isometric contractions in flexion, extension, ulnar deviation and radial deviation. The method then uses these EMG signals and the necessary anatomical data to estimate individual muscle forces. For one subject, complete anatomical parameters were estimated by MRI reconstruction of muscle moment arms and lines of muscle action. In all subjects, the errors associated with variability in the EMG signals were reduced through the use of signal processing techniques and intensive subject training. These EMG-based force estimates were then validated by evaluations at torque directions in which no mechanical redundancy existed. The stability of the solution space was examined using Monte Carlo simulations. The results of our study show that individual muscle forces at the wrist can be estimated with considerable accuracy, without assuming any control strategy (as is done with optimization theories). However, due to the limited mechanical redundancy of the wrist, it is uncertain whether the method can be used to estimate muscle forces in more highly redundant systems.

Stretch Reflex Adaptation in Elbow Flexors During Repeated Passive Movements in Unilateral Brain-Injured Patients

OBJECTIVE To evaluate the effects of repeated, externally imposed, flexion-extension movements of the elbow on the resulting stretch reflex response in hemiparetic spastic brain-injured patients. These effects were compared within a recording session and across sessions for the same subject to determine the impact of movement history on the quantification of spastic hypertonia using the stretch reflex response. DESIGN Twenty to 30 sequential, constant velocity flexion-extension movements were applied to the impaired elbow of our cohort, with a 10-second hold interposed between flexion and extension. Movements were applied regularly at 1-minute intervals. Changes in stretch reflex responses were monitored during the applied movements. PARTICIPANTS We examined a convenience sample of seven hemiparetic brain-injured subjects between the ages of 26 and 60 yrs, with moderate-to-severe spastic hypertonia of elbow muscles (Ashworth score 2-4/4). Subjects participated in 2 to 9 sessions. MEASURES Elbow torque, position, velocity, and electromyograms of the biceps, brachioradialis, and triceps muscles were recorded for each flexion and extension movement. Stretch reflex torque was calculated by subtracting passive torque from total elbow torque, recorded over large amplitude movements. A linear regression analysis quantified both the initial torque response of the stretch reflex and the ensuing adaptation of the stretch reflex during sequential movements. Intersession variability was characterized both for spastic hypertonia measures and for stretch reflex adaptation. RESULTS Repeated, externally imposed, sequential flexion-extension movements of the elbow decreased the elbow flexor stretch reflex in six of seven subjects. The mean reduction in reflex torque after 30 movements was 50% of the initial torque values (p = .001, t test vs. 0% change). Intersession stretch reflex responses for each subject were found to vary greatly (SDs of reflex torque ranged from 0.1 to 4.0 Nm), and there were also significant variations in the degree of adaptation between subjects. CONCLUSIONS Stretch reflex adaptation must be taken into consideration when spastic hypertonia is quantified using repeated joint motion, as is often the case. The magnitude of intersession variation in spastic hypertonia measures suggests that ideally, such measurements should be made across multiple sessions before conclusions are made regarding the efficacy of spastic hypertonia interventions. This study provides quantitative evidence that repeated joint movements may have a significant short-term beneficial effect on spastic hypertonia.

Quantitative features of the stretch response of extrinsic finger muscles in hemiparetic stroke

Despite its potential importance in hand dysfunction, spasticity in the finger muscles following stroke has not been well described. To explore this area, we assessed the role of finger flexor spasticity, along with that of passive mechanical forces, in resisting finger movement in 13 chronic stroke subjects. Subjects were tested with a device that stretched the extrinsic finger muscles through imposed rotation of the metacarpophalangeal (MCP) joints. Both maintained and constant‐velocity stretches were imposed. For the constant‐velocity stretches, eight of the 13 stroke subjects exhibited strong stretch reflexes, as determined by electromyography and net work. The net work of this reflex response, calculated from the integral of the torque‐angle plots, increased proportionally with increasing velocity, indicating a contribution from flexor muscle spasticity. Conversely, nine of the 13 stroke subjects did not possess distinctly greater passive, mechanical resistance to MCP rotation than control subjects. While extensor spasticity was not observed, stretch of the extrinsic finger flexors also produced some reflex activity in the finger extensors concomitant with reflex excitation of the flexors. These findings suggest that resistance to muscle stretching following stoke is mediated primarily by neurological rather than biomechanical disturbances, although changes in muscle fiber length may exaggerate the resistance.

Flexor reflexes in chronic spinal cord injury triggered by imposed ankle rotation

Hypersensitivity of the flexor reflexes to input from force‐sensitive muscle afferents may contribute to the prevalence and severity of muscle spasms in patients with spinal cord injuries. In the present study, we triggered flexor reflexes with constant‐velocity ankle movements into end‐range dorsiflexion and plantarflexion positions in 8 individuals with spinal cord injuries. We found that all 8 subjects had coordinated increases in flexion torque at the hip and ankle following externally imposed plantarflexion movements at the ankle. In addition, end‐range dorsiflexion movements also triggered flexor reflexes in 3 subjects, although greater loads were required to trigger such reflexes using dorsiflexion movements (compared to plantarflexion movements). These three‐joint reflex torque patterns triggered by ankle movement were broadly comparable to flexion withdrawal responses elicited by electrocutaneous stimuli applied to a toe, although the amplitude of the torque response was generally lower. We conclude that excitation of muscle and joint‐related afferents induced by end‐range movements may be responsible for exaggerated flexion reflex responses in spinal cord injury.

Reflex Torque Response to Movement of the Spastic Elbow: Theoretical Analyses and Implications for Quantification of Spasticity

AbstractA parametric model of the human reflex torque response to a large-amplitude, constant angular velocity elbow extension was developed in order to help quantify spasticity in hemiparetic stroke patients, and to better understand its pathophysiology. The model accounted for the routinely observed leveling of torque (i.e., a plateau) at a mean angular increment of 51°±10° s.d. (n=98) after the initial rise. This torque “plateau” was observed in all eight subjects, and in 98 of 125 trials across 25 experimental sessions. The occurrence of this plateau cannot be explained by decreases in elbow flexor moment arms during elbow extension. Rather, the plateau is attributable to a consistent leveling in muscle activation as confirmed both qualitatively from recordings of rectified, smoothed electromyograph (EMG) activity, and quantitatively using an EMG coefficient model. A parametric model was developed in which the pattern of muscle activation in the stretch reflex response of elbow flexors was described as a cumulative normal distribution with respect to joint angle. Two activation functions, one related to biceps and the other to brachioradialis/brachialis, were incorporated into the model in order to account for observations of a bimodal angular stiffness profile. The resulting model yielded biologically plausible parameters of the stretch reflex response which may prove useful for quantifying spasticity. In addition, the model parameters had clear pathophysiological analogs, which may help us understand the nature of the stretch reflex response in spastic muscles.

Separate Quantification of Reflex and Nonreflex Components of Spastic Hypertonia in Chronic Hemiparesis

OBJECTIVES To isolate and quantify reflex and nonreflex components of the spastic ankle plantarflexors in hemiplegia poststroke and to correlate them with clinical measures of spasticity, which may involve hyperactive stretch reflex and/or increased joint stiffness. DESIGN To investigate reflex and nonreflex properties associated with spasticity in a case-control manner. SETTING Research laboratory in a rehabilitation hospital. PARTICIPANTS Hemiplegic patients (n=17) and the same number of healthy subjects. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Tendon reflexes of spastic muscles were evaluated under an isometric condition, which essentially eliminated passive viscoelastic contributions associated with limb movement. Nonreflex components of spasticity were evaluated by moving the ankle joint slowly, which minimized reflex actions. The reflex and nonreflex measures were investigated and correlated with each other and with clinical measures. RESULTS Compared with healthy subjects, patients with stroke showed a lower reflex threshold, higher electromyographic gains, and torque reflex gains, indicating hyperactive reflexes. For nonreflex properties, ankles of stroke patients showed higher stiffness, reduced range of motion (ROM), and larger resistant torque at comparable positions, reflecting peripheral soft-tissue changes at the ankle of the chronic stroke patients. Furthermore, the clinical reflex score correlated with all of the quantitative reflex measures but not with the nonreflex measures, whereas the dorsiflexion ROM showed a significant correlation with a nonreflex measure. The Modified Ashworth Scale was correlated with all of the reflex measures and 1 of the nonreflex measures. CONCLUSIONS Comprehensive and convenient evaluation of spasticity should be performed quantitatively with the separate measures of reflex and nonreflex components, especially in chronic conditions. With proper simplifications, the current method of separate quantification can potentially be used for convenient clinical evaluations of spasticity.