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 (V) over dot O-2) 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 (V) over dot O-2 max and to cause fatigue in similar to5 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 (V) over dot O(2)response was influenced by exercise mode [(V) over dot O(2)max was achieved after 115 (20) s in running versus 207 (36) s in cycling; p<0.01]. (V) over dot O-2 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 I terms [2327 (393) ml.min(-1) versus 2036 (30 1) ml.min(-1); p = 0.02] but not when it was expressed as a percentage of the total increase in (V) over dot O-2 [86 (6)% versus 82 (6)%; p = 0.09]. When quantified as the difference between the end-exercise (V) over dot O-2 and the (V) over dot O-2 at 2 min, the amplitude of the slow component was similar to40% 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 (V) over dot O-2 response at equivalent intensities in the severe domain.