Establishing the V<scp>o</scp>₂ versus constant-work-rate relationship from ramp-incremental exercise: simple strategies for an unsolved problem

Abstract

The dissociation between constant work rate of O₂ uptake (V̇o₂) and ramp V̇o₂ at a given work rate might be mitigated during slowly increasing ramp protocols. This study characterized the V̇o₂ dynamics in response to five different ramp protocols and constant-work-rate trials at the maximal metabolic steady state (MMSS) to characterize <i>1</i>) the V̇o₂ gain (G) in the moderate, heavy, and severe domains, <i>2</i>) the mean response time of V̇o₂ (MRT), and <i>3</i>) the work rates at lactate threshold (LT) and respiratory compensation point (RCP). Eleven young individuals performed five ramp tests (5, 10, 15, 25, and 30 W/min), four to five time-to-exhaustions for critical power estimation, and two to three constant-work-rate trials for confirmation of the work rate at MMSS. G was greatest during the slowest ramp and progressively decreased with increasing ramp slopes (from ~12 to ~8 ml·min^-1·W^-1, <i>P</i> < 0.05). The MRT was smallest during the slowest ramp slopes and progressively increased with faster ramp slopes (1 ± 1, 2 ± 1, 5 ± 3, and 10 ± 4, 15 ± 6 W, <i>P</i> < 0.05). After "left shifting" the ramp V̇o₂ by the MRT, the work rate at LT was constant regardless of the ramp slope (~150 W, <i>P</i> > 0.05). The work rate at MMSS was 215 ± 55 W and was similar and highly correlated with the work rate at RCP during the 5 W/min ramp (<i>P</i> > 0.05, <i>r</i> = 0.99; Lin's concordance coefficient = 0.99; bias = -3 W; root mean square error = 6 W). Findings showed that the dynamics of V̇o₂ (i.e., G) during ramp exercise explain the apparent dichotomy existing with constant-work-rate exercise. When these dynamics are appropriately "resolved", LT is constant regardless of the ramp slope of choice, and RCP and MMSS display minimal variations between each other.<b>NEW & NOTEWORTHY</b> This study demonstrates that the dynamics of V̇o₂ during ramp-incremental exercise are dependent on the characteristics of the increments in work rate, such that during slow-incrementing ramp protocols the magnitude of the dissociation between ramp V̇o₂ and constant V̇o₂ at a given work rate is reduced. Accurately accounting for these dynamics ensures correct characterizations of the V̇o₂ kinetics at ramp onset and allows appropriate comparisons between ramp and constant-work-rate exercise-derived indexes of exercise intensity.