Fatigue patterns during second bouts of rhythmic and sustained exercise as a function of intertrial rest

College men (N=72) were assigned at random to four permutations of activity, either 1 min. of sustained maximal grip flexion or 3 min. of rhythmic exercise at a cadence of 42 contractions/min. Each was separated by a rest interval of 5, 10, 20, 40, 80, 160, or 320 sec. All Ss were tested with each interval of inter-bout recovery. Fatigue was evaluated by recording the strength exerted at each 5-sec. interval for the sustained bouts and each 15-sec. interval for the rhythmic bouts. Second-bout fatigue curves revealed that: (1) the rate of fatigue increased as a direct function of the length of intertrial recovery interval, (2) the fatigue pattern was controlled by the type of exercise performed during the session, (3) the asymptotic values toward which fatigue progressed were similar within groups but variant among the four activity permutations, and (4) within each family of curves there was a change in the form of the exponential equations required to describe the patterns of fatigue.