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 volunta ry torques (MVTs) generated isometrically in elbow flexion and extension un der four task conditions: without explicit control of the torques at adjace nt joints and in combination with each of three submaximal shoulder abducti on adduction torque levels. Setting: Rehabilitation center research laboratory. Patients: Volunteer samples of six patients with chronic hemiparesis and fo ur controls. Main Outcome Measure: Residual strength (RS), defined as the ratio of MVTs for the paretic and nonparetic limbs of patients and nondominant and domina nt 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 lev el, elbow flexion RS increased and elbow extension RS decreased. In contras t, for the control group, the effect of task condition on RS was not signif icant. Conclusion: In hemiparetic patients, weakness of the paretic elbow musculat ure shows a strong task dependence. This task dependence likely reflects th e existence of abnormal synergies between elbow and shoulder muscles of the paretic limb and has important implications for the rehabilitation of moto r function following hemiparesis. (C) 1999 by the American Congress of Reha bilitation Medicine ann the American Academy of Physical Medicine and Rehab ilitation.