Oxygen uptake plateau occurrence depends on oxygen kinetics and oxygen deficit accumulation

Abstract

We tested the hypothesis that participants with an oxygen uptake ( $\dot{V}{O}_2$ ) plateau during incremental exercise exhibit a lower VO₂ -deficit (VO_2DEF )-accumulation in the submaximal intensity domain due to faster ramp and square wave O₂ -kinetics. Twenty-six male participants performed a standard ramp test (increment: 30 W·min^-1 ), a ramp test with an individualized ramp slope and a two-step (moderate and severe) square wave exercise followed by a $\dot{V}{O}_{2max}$ -verification bout. VO_2DEF was calculated by the difference between individualized ramp test $\dot{V}$ O₂ and $\dot{V}$ O₂ -demand estimated from steady-state $\dot{V}$ O₂ -kinetics. Twenty-four participants verified their $\dot{V}$ O_2max in the verification test. Ten of them showed a plateau in the individualized ramp test. VO_2DEF at the end of this ramp test (4.34 ± 0.60 vs 4.54 ± 0.43 L) was not different between the plateau and the non-plateau group (P > 0.05). The plateau group had a significantly (P < 0.05) lower VO_2DEF 2 minutes before termination of the individualized ramp test (2.24 ± 0.40 vs 2.78 ± 0.33 L). This coincided with a shorter mean response time (43 ± 9 vs 53 ± 7 seconds), a higher increase in $\dot{V}$ O₂ per W (10.1 ± 0.2 vs 9.2 ± 0.5 mL·min^-1 ·W^-1 ) at the individualized ramp test as well as shorter time constants of moderate (36 ± 6 vs 48 ± 7 seconds) and severe (62 ± 9 vs 86 ± 10 seconds) square wave kinetics (all P < 0.05). We conclude that the $\dot{V}$ O₂ -plateau occurrence requires a fast $\dot{V}$ O₂ -kinetics and a low VO_2DEF -accumulation at intensities below $\dot{V}$ O_2max .

Keywords: anaerobic; cardiorespiratory fitness; endurance; exercise testing; levelling-off.