Speed-dependent reductions of force output in people with poststroke hemiparesis

Background and Purpose. Movement is slow in people with poststroke hemipare sis. Moving at faster speeds is thought by some researchers to exacerbate a bnormal or unwanted muscle activity. The purpose of this study was to quant ify the effects of increased speed on motor performance during pedaling exe rcise in people with poststroke hemiparesis. Subjects. Twelve elderly subje cts with no known neurological impairment and 15 subjects with poststroke h emiparesis of greater than 6 months' duration were tested. Methods. Subject s pedaled at 12 randomly ordered workload and cadence combinations (45-, 90 -, 135-, and 180-J workloads at 25, 40, and 55 rpm). Pedal reaction forces were used to calculate work done by each lower extremity. Electromyographic activity was recorded from 7 lower-extremity muscles. Results. The main fi nding was that net mechanical work done by the paretic lower extremity decr eased as speed increased in all subjects. The occurrence of inappropriate m uscle activity on the paretic side, however, was not exacerbated in that th e vastus medialis muscle on the paretic side did not show a consistent furt her increase in its prolonged activity at higher speeds. The mechanics of f aster pedaling resulted in greater net negative mechanical work because, at higher pedaling rates, the prolonged vastus medialis muscle activity is pr esent during a greater portion of the cycle. Conclusion and Discussion. The lessened force output by the paretic limb is mainly the result of the inhe rent mechanical demands of higher-speed pedaling and not due to exacerbatio n of impaired neural control. [Brown DA, Kautz SA. Speed-dependent reductio ns of force output in people with poststroke hemiparesis.