Bimanual isometric force control: Asymmetry and coordination evidence post stroke

ObjectiveThis study determined the nature of bimanual deficits during visually-guided isometric force production in chronic stroke.MethodsStroke survivors and age-matched controls performed bimanual isometric wrist/finger extension contractions for 20 s to target submaximal force levels. Force asymmetry was indexed by the proportion of force contributed by the impaired hand to total force. Force coordination was determined by computing time-series cross-correlations and time-lag between force outputs of both hands.ResultsThe stroke group demonstrated greater asymmetry and reduced coordination in force produced by each hand. The extent of asymmetry in the force magnitude remained constant across the three submaximal force levels in both groups. Bimanual force coordination increased at higher forces in controls but not in stroke. Finally, the less-impaired hand forces time-lagged the impaired hand.ConclusionsBimanual motor impairments in chronic stroke are characterized by increased asymmetry and reduced coordination between individual hand forces. Distinct control mechanisms are involved in the production and coordination of forces following stroke.SignificanceAn implication involves rehabilitation protocols that emphasize bimanual coordination for training the hands to produce symmetric forces that are temporally coordinated.

► Stroke leads to increased asymmetry and reduced coordination between hands during a bimanual isometric force control task. ► Stroke survivors show more force control impairments with a smaller proportion of total force contributed by their impaired hand and a greater time-lag between hands during a bimanual task. ► Overall, the findings strongly suggest that movement benefits will accrue when rehabilitation protocols for the upper extremity train symmetry and coordination between hands.