Aim: VO2peak can be achieved over the range of intensities that define the severe intensity domain. The purpose of this study was to help characterize the VO2 response during constant-load exercise in this domain.
Methods: Twelve participants performed cycle ergometer tests at 267+/-52 W, 238+/-45 W, and 216+/-37 W, which were individually selected to elicit VO2peak and to cause fatigue in 3 min, 5 min, and 7 min, respectively.
Results: Times to fatigue were 201+/-16 s, 301+/-20 s, and 448+/-51 s, respectively. VO2 responded faster at higher work rates, with VO2peak reached after 154+/-25 s, 193+/-35 s, and 206+/-24 s, respectively. Extrapolation of the times to reach VO2peak revealed that 300 W was the highest power, and 151 s was the shortest time, for which VO2peak could be elicited. TheVO2 response was described using a three-component model. Exercise intensity did not affect the speed of the primary response, with time constants of 22+/-3 s, 23+/-4 s, and 23+/-4 s, respectively. However, the size of the primary phase was greater at higher intensities, with amplitudes of 1,798+/-200 mlxmin-1, 1,739+/-267 mlxmin-1, and 1,677+/-254 mlxmin-1, respectively. The amplitude of the slow component was correspondingly smaller at higher intensities. Extrapolation of the slow component amplitudes revealed that 299 W was the highest intensity, and 152(-1)53 s was the shortest time, for which a slow component would be engendered.
Conclusion: VO2peak is attained faster at higher intensities because the amplitude of the primary response is greater, not because the response is faster. There is a slow component to the VO2 response at all intensities within the severe domain, but not at higher intensities, in the extreme domain, where fatigue occurs before VO2peak can be elicited.