A simple method to determine the severe-extreme intensity exercise domain boundary using the VO₂ kinetic response

The boundary separating the severe intensity exercise domain, wherein the maximal O2 uptake (V.O2max) can be attained, from the extreme intensity exercise domain, wherein V.O2max cannot be attained, is not widely adopted in applied sports sciences due to the labour-intensive nature of its measurement. The aim of this study was to propose an alternative and practical approach to estimate the severe-extreme domain boundary using V.O2 kinetics. Sixteen males completed an incremental exercise test and a series of constant power output exercise tests on a cycle ergometer. The relationship between time to achieve V.O2max and time to task failure during severe-intensity exercise was calculated to estimate the highest power output at which V.O2max was momentarily attained before task failure (PUPPERBOUND). Separately, the highest power output that provided a time to task failure that was equal to or greater than four times the time constant (tau) describing the V.O2 kinetics during severe-intensity exercise (P4-tau) was calculated. The PUPPERBOUND and P4-tau occurred at similar power outputs (379 vs. 380 W; p = 0.62) and were closely related (r:0.99; bias:1 W; SEE:7 W; CV%:1.92%; LoA:-14 W to 16 W). Compared to PUPPERBOUND, the P4-tau method provides a simpler and more time efficient approach to identify the severe-extreme domain boundary.