Recovery of submaximal upper limb force production is correlated with better arm position control and motor impairment early after a stroke

ObjectiveThis study determined whether recovery of upper limb position control using submaximal force production correlates with an improvement in functional arm impairment during early recovery from stroke.MethodsTen consecutive inpatients were recruited from a stroke unit. Each patient was in early recovery (<8 weeks post-lesion) from their first ever stroke. Evaluations of submaximal continuous force production and position control, maximal force production at the shoulder and a clinical outcome measure of motor impairment (Fugl-Meyer score; FM) were performed 20 days post-stroke as a baseline and then once a week for the following four weeks.ResultsSubmaximal force production and its modulation during a position-holding task improved in early recovery after stroke, whereas maximal force production did not. Better modulation of submaximal force production enabled improved arm position control which was significantly correlated to the changes in FM score of motor impairment during recovery.ConclusionsThis study demonstrated that improvement in submaximal force modulation can operate as a mechanism enabling better motor behaviour such as arm position control during early recovery from a stroke.SignificanceFuture rehabilitation strategies may benefit from adding submaximal force development and modulation to early interventions after stroke.

► Position control during a continuously changing task depends on precise control of submaximal force production and is often disrupted by stroke. ► Continuous time-varying force modulation recovered early after stroke, whereas maximal force production did not. ► Recovery of force modulation led to better position control and this was correlated with changes in upper arm motor impairment.