Comparison of strength measurements under single-joint and multi-joint conditions in hemiparetic individuals

OBJECTIVE: It has been suggested that the measurement of strength is inappropriate in patients with stroke, in large part because of the presence of abnormal synergy patterns. The aim of the present study was to characterize force production during multi-joint maximal exertion involving different combinations of activation between shoulder and elbow flexors and extensors. DESIGN: Cross-sectional study. SETTING: Rehabilitation centre. SUBJECTS: A convenience sample of 16 chronic hemiparetic stroke subjects. MAIN OUTCOME MEASURES: Maximal torques in flexion and extension at the shoulder and the elbow were measured using static dynamometers (single-joint condition). In addition, the maximal forces produced at the wrist were measured in four directions in the sagittal plane requiring different torque combinations between shoulder and elbow flexors and extensors (multi-joint condition). RESULTS: No difference was found across directions for the ratios of maximal forces (paretic/nonparetic) in the multi-joint condition (p = 0.227; mean ratios (+/- SD) for each direction ranging from 0.59+/-0.23 to 0.68+/-0.27), suggesting that the ability to produce force did not change as a function of the required torque combination. In addition, relative torques (% of the maximal torque in the single-joint condition) exerted during the multi-joint exertions were similar on the paretic and the nonparetic side. CONCLUSIONS: These results do not support the assumption that force production is limited by abnormal synergy patterns between flexors and extensors at the shoulder and the elbow in hemiparetic patients.