This study was undertaken to compare the variance in time to fatigue (TF) at intensities expressed relative to VO2max, ventilation threshold 1 (VT1) or 2 (VT2). Two 3-min, 30 Watt incremental tests on the cycle ergometer were used to determine VO2max (50.7 +/- 7.2 ml X kg-1 X min-1), VT1 (51.7 +/- 3.7% VO2max) and VT2 (79.0 +/- 3.7% VO2max) for 16 subjects. At weekly intervals, subjects worked to volitional fatigue at 3 randomly-ordered power outputs that represented 73.1 +/- 2.8, 85.4 +/- 2.8 and 95.0 +/- 3.4% VO2max. A significant quadratic interaction was observed for TF values between VO2max and intensity, suggesting a different magnitude of response related to VO2max. Subject data were then grouped according to VO2max into a low (N = 5, 40-44 ml X kg-1 X min-1), medium (N = 5, 48-52 ml X kg-1 X min-1) or high (N = 6, 56-61 ml X kg-1 X min-1) category. For all groups, a decaying exponential function best described the relationship between TF and intensity. The method of expressing intensity appeared to have only a small effect on the proportion of variance explained by this logarithmic relationship (0.85 less than or equal to r2 less than or equal to 0.93). In contrast, however, a 30% reduction in the standard error of estimate for TF was observed when intensity was expressed relative to both ventilation thresholds as compared to the traditional expression of intensity relative to VO2max.(ABSTRACT TRUNCATED AT 250 WORDS)