The purpose of this study was to assess the significance of the velocity at which an individual achieves VO2max in an incremental treadmill test (Vmax) and the time that this velocity can be sustained (Tmax) to evaluate the rationale for using Vmax and Tmax in the prescription of endurance exercise training. Mean (+/- SD) values for VO2max, and Vmax in 13 female track athletes were 52.1 +/- 5.1 ml.kg.min-1 and 271 +/- 18 m.min-1, respectively. Then each athlete performed an exhaustive run at her Vmax. In these runs, VO2max was achieved after 234 +/- 49 s and was maintained for 56 +/- 48 s (range, 10-155 s) which was the last 18 +/- 13% (range, 4-47%) of the total exercise bout. Only one of the 13 subjects reached VO2max in the first 60% of the constant velocity test. Thus, while VO2max was attained during exhaustive exercise at Vmax, the amount of time that it was sustained was quite small (less than 60 s) and highly variable. It was concluded that Vmax is a suitable intensity to elicit VO2max in training. But 60% (or less) of Tmax is not an appropriate duration for training at this intensity because it is too short a time to allow most athletes to reach VO2max.