V̇O _2max may not be reached during exercise to exhaustion above critical power

Purpose: This study was designed to determine whether V̇O ₂ reaches a maximum, equivalent to that attained in an incremental exercise test to exhaustion, during "submaximal" fatigue-inducing constant-power exercise bouts above critical power (CP). Methods: Nine males (age = 24.6 ± 3.6 yr, height = 182.8 ± 6.9 cm, weight = 77.8 ± 12.1 kg) and four females (age = 29.0 ± 7.3 yr, height = 170.8 ± 3.2 cm, weight = 61.8 ± 8.2 kg) underwent an incremental V̇O _2max test (IET) on a cycle ergometer, followed by four or five randomly assigned constant-power exercise bouts to exhaustion, on separate days. The CP for each subject was estimated using linear and nonlinear regression. Results: IET V̇O _2max averaged 3.55 ± 0.92 L•min (RER = 1.21 ± 0.05, HR = 186 ± 10 bpm, 96.1% ± 6.3% of age-predicted maximum). Mean peak V̇O ₂ (range = 3.32 ± 0.88 to 3.54 ± 0.91 L•min) during the three highest constant-power bouts (two of which were 53 to 82 W less than peak power output attained during IET) was not significantly different from IET V̇O _2max. Eleven of 13 subjects exceeded their IET V̇O _2max during at least one of the constant-power exercise bouts. However, peak V̇O ₂ (3.11 ± 0.79 L•min) during the lowest constant-power exercise bout, which ranged from 10 to 36 W above CP estimated with a two-parameter nonlinear model, was significantly lower than IET V̇O _2max (88.2% ± 9.4% of IET V̇O _2max). Conclusions: At power outputs above CP, V̇O ₂ does not necessarily increase to maximum during constant-power exercise to exhaustion. In addition, the highest V̇O ₂ values measured during a traditional V̇O ₂ "max" test (i.e., IET) may not reflect the highest attainable V̇O ₂ despite V̇O _2max criteria being met.