Deficits of predictive grip force control during object manipulation in acute stroke

Anticipatory grip force adjustments when lifting, holding and performing vertical point-to-point movements with a hand-held object were analysed in 11 patients with deficits of fine manual motor performance due to acute ischemic stroke. All patients had mild to moderate paresis and sensory deficits of the affected hand. Grip forces used to stabilise the object in the hand, accelerations of the object and movement-induced loads were measured. Compared with controls, patients produced markedly increased grip forces when lifting, holding and moving the hand-held object. The ratio between grip force and the actual load, which is considered to be a sensitive measure of force efficiency, was significantly elevated in stroke patients indicating a strategic generalisation of grip force increase when cerebral sensorimotor areas are functionally impaired. The temporal coupling between grip and load force profiles revealed only selective impairments during the lifting and movement tasks of stroke patients. The time to reach maximum grip force was prolonged and there were greater time lags between grip and load force maxima during the lifting movements. When healthy controls performed vertical movements with the hand-held object grip force increased early in upward and late in downward movements and grip and load force maxima coincided closely in time. The time lags between maximum grip and load forces were similar for vertical movements performed by patients and controls. However, the time lags between grip force and acceleration onset were larger for upward and smaller for downward movements performed by stroke patients. These findings indicate impaired prediction of the inertial load profiles arising from voluntary arm movements with a handheld object in acute stroke.