Phase III V̇O₂ increase does not lead to V̇O₂ values higher than V̇O_2max during prolonged intense exercises in humans

Abstract

This study tested the hypothesis that maximum O₂ uptake (V̇O_2max) sets the uppermost limit to O₂ flow. If this is so, the V̇O₂ increase with time during high intensity prolonged exercises (slow component) cannot reach V̇O₂ levels higher than V̇O_2max. To this aim, on 15 amateur cyclists (age, 24±4 years; mean ± S.E.M.) V̇O_2max was measured during graded cycloergometric exercise. On different days, the subjects performed exercises at 80% and 90% of the previously determined V̇O_2max up to exhaustion (Ẇ₈₀ and Ẇ₉₀, respectively). Measured variables included time to exhaustion (T_lim), power output, V̇O₂, CO₂ production (V̇CO₂), ventilation (V̇E) and blood lactate concentration ([La]). V̇O_2max was 4.05±0.08 L•min^-1. At the end of Ẇ₈₀ (T_lim 1649±145 s) and Ẇ₉₀ (T_lim 733±65 s), V̇O₂ was 3.77±0.13 and 4.08±0.12 L•min^-1 respectively. V̇O₂ at the end of Ẇ₉₀ was similar to V̇O_2max, while at the end of Ẇ₈₀ 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 V̇E and V̇CO₂ at the end of Ẇ₈₀ and Ẇ₉₀. In conclusion, the present results support the hypothesis that V̇O_2max really reflects the individual maximum aerobic power, without being limited by factors intrinsic to the experimental procedures.