The V̇O₂ slow component for severe exercise depends on type of exercise and is not correlated with time to fatigue

The purpose of this study was to examine the influence of the type of exercise (running vs. cycling) on the O₂ uptake (V̇O₂) slow component. Ten triathletes performed exhaustive exercise on a treadmill and on a cycloergometer at a work rate corresponding to 90% of maximal V̇O₂ (90% work rate maximal V̇O₂). The duration of the tests before exhaustion was superimposable for both type of exercises (10 min 37 s ± 4 min 11 s vs. 10 min 54 s ± 4 min 47 s for running and cycling, respectively). The V̇O₂ slow component (difference between V̇O₂ at the last minute and minute 3 of exercise) was significantly lower during running compared with cycling (20.9 ± 2 vs. 268.8 ± 24 ml/min). Consequently, there was no relationship between the magnitude of the V̇O₂ slow component and the time to fatigue. Finally, because blood lactate levels at the end of the tests were similar for both running (7.2 ± 1.9 mmol/1) and cycling (7.3 ± 2.4 mmol/l), there was a clear dissociation between blood lactate and the V̇O₂ slow component during running. These data demonstrate that 1) the V̇O₂ slow component depends on the type of exercise in a group of triathletes and 2) the time to fatigue is independent of the magnitude of the V̇O₂ slow component and blood lactate concentration. It is speculated that the difference in muscular contraction regimen between running and cycling could account for the difference in the V̇O₂ slow component.