Transient changes in paretic and non-paretic isometric force control during bimanual submaximal and maximal contractions

Purpose The purpose of this study was to investigate transient bimanual effects on the force control capabilities of the paretic and non-paretic arms in individuals post stroke across submaximal and maximal force control tasks. Methods Fourteen chronic stroke patients (mean age = 63.8 +/- 15.9; stroke duration = 38.7 +/- 45.2 months) completed two isometric force control tasks: (a) submaximal control and (b) maximal sustained force production. Participants executed both tasks with their wrist and fingers extending across unimanual (paretic and non-paretic arms) and bimanual conditions. Mean force, force variability using coefficient of variation, force regularity using sample entropy were calculated for each condition. Results During the submaximal force control tasks (i.e., 5, 25, and 50% of maximum voluntary contraction), the asymmetrical mean force between the paretic and non-paretic arms decreased from unimanual to bimanual conditions. The asymmetry of force variability and regularity between the two arms while executing unimanual force control tended to decrease in the bimanual condition because of greater increases in the force variability and regularity for the non-paretic arm than those for the paretic arm. During the maximal sustained force production tasks (i.e., 100% of maximum voluntary contraction), the paretic arm increased maximal forces and decreased force variability in the bimanual condition, whereas the non-paretic arm reduced maximal forces and elevated force variability from unimanual to bimanual conditions. Conclusions The current findings support a proposition that repetitive bimanual isometric training with higher execution intensity may facilitate progress toward stroke motor recovery.