The hyperbolic relationship between power output (P) and time to exhaustion (t) is described as t = W'/(P-theta PA). The purpose of this study was to determine the stability of estimations of estimates of theta PA and W', said to reflect maximal sustainable power and anaerobic capacity, respectively. Thirteen women and 13 men performed five bouts of cycling exercise to exhaustion. Individual theta PA and W' were calculated from the results of these five bouts (Trial 1). These procedures were repeated (Trial 2). For both sexes, Trial 2 estimates of theta PA were 5 to 6% higher than Trial 1 estimates, but they were highly correlated. Mean W' estimates were the same in Trials 1 and 2, with higher trial-to-trial correlations in the men than in the women.