Modifiability of abnormal isometric elbow and shoulder joint torque coupling after stroke

Abstract

Unlike individuals with mild stroke, individuals with severe stroke are constrained to stereotypical movement patterns attributed to abnormal coupling of shoulder abductors with elbow flexors, and shoulder adductors with elbow extensors. Whether abnormal muscle coactivation and associated joint torque patterns can be changed in this population is important to determine given that it bears on the development of effective rehabilitation interventions. Eight subjects participated in a protocol that was designed to reduce abnormal elbow/shoulder joint torque coupling by training them to generate combinations of isometric elbow and shoulder joint torques away from the constraining patterns. After training, subjects demonstrated a significant reduction in abnormal torque coupling and a subsequent significant increase in ability to generate torque patterns away from the abnormal pattern. We suggest the rapid time-course of these changes reflects a residual capacity of the central nervous system to adapt to a novel behavioral training environment.

Figures

FIGURE 1

Image of the experimental arrangement: A—forearm interface plate mounted directly to load cell; B—fiberglass cast; C— 6-DOF load cell; D—Delrin cast interface ring; E—video feedback monitor.

FIGURE 2

Isometric shoulder flexion (SF), shoulder abduction (AB), and elbow extension (EE) torque indicated by arrows superimposed on the visual feedback display viewed by the right-handed subject.

FIGURE 3

Mean normalized joint torque patterns and standard errors on the first (1) and last (24) training sessions are illustrated for each isometric multi-DOF task. In task 1 (A), the subject attempted to maximize shoulder flexion (SF), shoulder abduction (AB), and elbow extension (EE) torque directions. In task 2 (B), the subject attempted to maximize AB and EE and was blinded to the shoulder flexion/extension DOF. In task 3 (C), the subject attempted to maximize SF and EE and was blinded to the shoulder abduction/adduction (AB/AD) DOF. Significant pre- vs. post-training improvements are indicated, supporting the ability of subjects to generate greater concurrent joint torques away from the abnormal pattern. Asterisk denotes difference between sessions at the 0.05 level of significance.

FIGURE 4

Mean percent improvement and standard error in single-DOF torque directions of shoulder flexion (SF), extension (SE), abduction (AB), adduction (AD), and elbow extension (EE) and flexion (EF) in both the 70° (A) and 90° limb (B) configurations. Asterisk denotes significant difference from zero.

FIGURE 5

Individual-subject (subjects 1– 8) pre- and posttraining spontaneous elbow-flexion (EF) torque (normalized to maximum within session) during maximal shoulder abduction (AB) at 70° (A) and 90° (B) limb configurations. The graphs illustrate the overall reduction in abnormal joint torque coupling in both limb positions after training.