Energy balance analysis suggests that lactate is not a direct cause of the slow component of oxygen uptake kinetics

Abstract

Purpose: The mechanisms of oxygen uptake ( $\dot{\text{V}}{\text{O}}_2$ ) slow component in the severe exercise intensity domain are still a matter of debate. We tested the hypothesis that the rate of blood lactate ([La]) accumulation above maximal lactate steady state (MLSS) is a major cause of $\dot{\text{V}}{\text{O}}_2$ slow component.

Methods: On 13 males exercising on a cycle-ergometer, we measured gas exchanges, heart rate, and [La] during maximal incremental exercise test to determine maximal aerobic power ( $\stackrel{.}{\text{w}}$ _max) and at constant power exercise tests at 60%, 65%, 70%, and 80% of $\stackrel{.}{\text{w}}$ _max.

Results: Maximal $\dot{\text{V}}{\text{O}}_2$ was 3.19 ± 0.37 l·min^-1, $\stackrel{.}{\text{w}}$ _max was 283 ± 28 W. At 60% $\stackrel{.}{\text{w}}$ _max all variables attained steady state in all subjects. Power at MLSS was 177 ± 21 W. At 80% $\stackrel{.}{\text{w}}$ _max a clear $\dot{\text{V}}{\text{O}}_2$ slow component was observed in all subjects, exercise lasted 11.3 ± 3.1 min and [La] was 7.4 ± 2.2 mmol at 5 min and 11.5 ± 3.6 mmol at 10 min. The energy balance computed at 80% $\stackrel{.}{\text{w}}$ _max resulted compatible with the principles of the energetics of muscular exercise, if we assume linear [La] increase, and thus constant metabolic power provided by [La] accumulation. Conversely, the metabolic power provided by $\dot{\text{V}}{\text{O}}_2$ slow component increases with time. This contrast is incompatible with the tested hypothesis that consequently must be rejected.

Conclusion: This study excluded [La] accumulation as a main cause of $\dot{\text{V}}{\text{O}}_2$ slow component.

Keywords: Energetics; Exercise; Kinetics; Oxygen consumption; Slow component.