Background and Purpose - A principle of poststroke rehabilitation is that effort should be avoided since it leads to increased spasticity and produces widespread associated abnormal reactions. Although weakness also contributes to movement dysfunction after a stroke, it has been feared that heightened activity levels during strength training will further exacerbate the abnormal tone imbalance present in spastic hemiplegia. The purpose of this study was to test this hypothesis by quantifying the effects of increased workload on motor performance during different speeds of pedaling exercise in persons with poststroke hemiplegia. Methods - Twelve healthy elderly subjects and 15 subjects with poststroke hemiplegia of greater than 6 months since onset were tested. The experimental protocol consisted of having subjects pedal at 12 randomly ordered workload and cadence combinations (45- J, 90-J, 135-J, and 180-J workloads at 25, 40, and 55 rpm). Pedal reaction forces were measured and used to calculate work done by each leg, including net positive and negative components. An electromyogram was recorded from seven leg muscles. Results - The main finding was that net mechanical work done by the plegic leg increased as workload increased in 75 of 81 instances without increasing the percentage of inappropriate muscle activity. Conclusions - This study provides evidence that persons with hemiplegia increase force output by their plegic limb when pedaling against higher workloads without exacerbation of impaired motor control. Therefore, exertional pedaling exercise is a beneficial intervention for achieving gains in muscular force output without worsening motor control impairments.