In an effort to identify neuromuscular parameters which differentiate between power-type and endurance-type athletes, an investigation was conducted to determine the effects of an isometric exercise task upon patellar and Achilles fractionated reflex time components in a group of weight lifters and long-distance runners. A reflex hammer was used to deliver a tendon tap stimulus to the patellar tendon (sitting position) and the Achilles tendon (prone position). Under resting conditions, no differences in Achilles reflex components existed between the two subject groups. However, patellar reflex latency was significantly shorter in the weight lifters than in the distance runners. Following knee extensor exercise consisting of three bouts of a 50% MVC holding-time task, the power group manifested a marked lengthening in total reflex time and reflex motor time. In the endurance group, reflex time lengthened after the first bout, but became shorter after the last two bouts. A similar Achilles reflex pattern was seen in both groups after plantar flexor exercise--an initial elongation of the peripheral components of reflex time, followed by a trend towards shorter reflex components in the later bouts. It was suggested that several factors may be competing to produce the bi-directional results observed in reflex time components following isometric exercise.