Serial isometric fatigue functions with variable intertrial intervals

The maximum voluntary strength of 60 Ss was measured during 10 successive 25-sec. trials separated by rest periods of 25, 50, or 100 sec. The intertrial intervals within a session were constant. The adjustment to the various work-rest schedules occurred early in the trial series. When the reduction in mean output was taken as 100% for each rest condition, the loss between the first 2 trials was 33%, 35%, and 24% for the 25-, 50, and 100-sec. conditions, respectively. An equation derived by a multiple regression analysis with the number of previous trials, intertrial intervals, and contraction time as independent variables produced a set of predicted values which correlated .99 with the actual means. This analysis indicated that the fatigue functions may be assumed to be identical in form for the various trials at the different intertrial intervals. Strength was significantly correlated with absolute decrement but not with relative decrement.