Phase III VO2 increase does not lead to VO2 values higher than VO2max during prolonged intense exercise in humans

This study tested the hypothesis that maximum O2 uptake (V˙ O2max) sets the uppermost limit to O2 flow. If thisis so, the V˙O2 increase with time during high intensity prolonged exercises (slow component) cannot reach V˙ O2 levels higher than V˙ O2max. To this aim, on 15 amateur cyclists (age, 24±4 years; mean ± S.E.M.) V˙ O2max was measured during graded cycloergometric exercise. On different days, the subjects performed exercises at 80% and 90% of the previously determined V˙O2max up to exhaustion (W˙ 80 and W˙ 90, respectively). Measured variables included time to exhaustion (Tlim), power output, V˙O2, CO2 production (V˙ CO2), ventilation (V˙E) and blood lactate concentration ([La]). V˙ O2max was 4.05±0.08•min-1. At the end of W˙ 80 (Tlim 1649±145 s) and W˙ 90 (Tlim 733±65 s), V˙ O2 was 3.77±0.13 and 4.08±0.12 L•min-1 respectively. V˙O2 at the end of W˙ 90 was similar to V˙O2max, while at the end of W˙ 80 it was significantly lower. [La] was increased at the end of prolonged exercises not only with respect to rest, but also compared to values at exercise minute 5, indicating anaerobic lactic metabolism contribution to energy production. Compensation of lactic acidosis led to significant increases in V˙ E and V˙ CO2 at the end of W˙ 80 and W˙ 90. In conclusion, the present results support the hypothesis that V˙O2max really reflects the individual maximum aerobic power, without being limited by factors intrinsic to the experimental procedures