Oxygen uptake kinetics during severe intensity running and cycling

The purpose of this study was to investigate the effect of exercise mode on the characteristics of the oxygen uptake ( V̇O2) response to exercise within the severe intensity domain. Twelve participants each performed a treadmill running test and a cycle ergometer test to fatigue at intensities selected to elicit a mode-specific V̇O2max and to cause fatigue in ~5 min. The tests were at 234 (30) m·min−1 and 251 (59) W, and times to fatigue were 297 (15) s and 298 (14) s, respectively. The overall rapidity of the V̇O2response was influenced by exercise mode [ V̇O2max was achieved after 115 (20) s in running versus 207 (36) s in cycling; p<0.01]. V̇O2 responses were fit to a three-phase exponential model. The time constant of the primary phase was faster in treadmill tests than in cycle ergometer tests [14 (6) s versus 25 (4) s; p<0.01], and the amplitude of the primary phase was greater in running than in cycling when it was expressed in absolute terms [2327 (393) ml·min−1 versus 2036 (301) ml·min−1; p=0.02] but not when it was expressed as a percentage of the total increase in V̇O2 [86 (6)% versus 82 (6)%; p=0.09]. When quantified as the difference between the end-exercise V̇O2 and the V̇O2 at 2 min, the amplitude of the slow component was ~40% smaller in running [177 (92) ml·min−1 versus 299 (153) ml min−1; p=0.03]. It is concluded that exercise modality affects the characteristics of the V̇O2 response at equivalent intensities in the severe domain.