Task-dependent weakness at the elbow in patients with hemiparesis

Objective: To investigate the task dependence of elbow weakness in patients with hemiparesis. Design: Descriptive study based on interlimb comparisons of maximum voluntary torques (MVTs) generated isometrically in elbow flexion and extension under four task conditions: without explicit control of the torques at adjacent joints and in combination with each of three submaximal shoulder abduction adduction torque levels. Setting: Rehabilitation center research laboratory. Patients: Volunteer samples of six patients with chronic hemiparesis and four controls. Main Outcome Measure: Residual strength (RS), defined as the ratio of MVTs for the paretic and nonparetic limbs of patients and nondominant and dominant limbs of controls. Results: For the patient group a significant effect of task condition on RS was found (analysis of variance, p = .0003 and p = .002 for elbow flexion and extension, respectively). With increasing shoulder abduction torque level, elbow flexion RS increased and elbow extension RS decreased. In contrast, for the control group, the effect of task condition on RS was not significant. Conclusion: In hemiparetic patients, weakness of the paretic elbow musculature shows a strong task dependence. This task dependence likely reflects the existence of abnormal synergies between elbow and shoulder muscles of the paretic limb and has important implications for the rehabilitation of motor function following hemiparesis. (C) 1999 by the American Congress of Rehabilitation Medicine ann the American Academy of Physical Medicine and Rehabilitation.