Mechanical work and fatigue: their roles in the development of muscle work capacity

To compare the effects of mechanical work versus fatigue on the improvement of work capacity of muscle, young, healthy men were selected to life a 45-pound weight with their quadriceps for 30 sessions, followed by 5 sessions of testing. The study consisted of two phases. Subjects in the first phase did equal amounts of mechanical work with both quadriceps, but had different amounts of fatigue from side to side because the rate of work was different. Subjects in the second phase fatigued both quadriceps, but one quadriceps was fatigued with a rest period between contraction cycles, and one was fatigued without a rest period, thus allowing the side with the rest cycle to do more mechanical work. To test the relative effects of training, a transfer-of-training design was used in both phases. The results suggest that fatigue, defined operationally as the inability or unwillingness of the subject to continue the prescribed task under given reinforcement conditions, plays a larger role in the development of work capacity of muscle than the amount of mechanical work per se.