title: VO2 response profiles in severe intensity exercise.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Kinesiology, Health Promotion, and Recreation, University of North Texas, Denton, TX 76203-0769, USA. dhill@unt.edu
authors.forename: D W
authors.initials: DW
authors.lastname: Hill
authors.forename: E C
authors.initials: EC
authors.lastname: Stevens
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005221:Fatigue / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D010807:Physical Endurance; D011446:Prospective Studies; D013997:Time Factors