Inter-limb force coupling is resistant to distorted visual feedback in chronic hemiparetic stroke.

OBJECTIVE Interlimb coupling between impaired and non-impaired limbs after stroke has been a common observation. The aim of this study was to examine interlimb interactions in force production in responses to altered visual gain in hemiparetic stroke survivors. DESIGN prospective clinical study METHODS A convenient sample of 7 hemiparetic stroke subjects (3 women and 4 men; mean age 56.0 years (standard errors 12.8) of age; history of stroke: mean duration 61.6 months (standard errors 53.3)) participated in the study. Subjects performed bilateral elbow flexion to varying total force targets from 3% to 60% maximal contraction forces with normal visual gain (1:1) and to a 10% maximal voluntary contraction target with altered visual gains (1/8, 1/4, 1/2, 2, 4, and 8) for the force of the less-impaired, ipsilesional side. RESULTS Across all conditions, the forces produced by both impaired and non-impaired limb changed proportionally to their maximal voluntary contraction force, such that relative contributions of each limb's force to the total force remained unchanged. In conditions with altered visual gain, high and low, the total force showed errors in the direction of under-shooting. CONCLUSION Our findings indicate that there is a strong interlimb force coupling in hemiparetic stroke, resistant to distorted visual feedback. It may reflect a default sharing pattern dominant after stroke.