title: Respiratory muscle power and the slow component of O2 uptake.
abstract: OBJECTIVE
  The slow component of O2 uptake (V˙O2sc) represents a progressive decline in work efficiency during strenuous, constant work rate cycling. Although most of this "excess" O2 uptake can be explained by factors intrinsic to the exercising muscles, it has been proposed that respiratory muscle work rate may also contribute to the V˙O2sc response. To date, however, no study has provided a comprehensive analysis of the mechanical power of breathing (Pb) in relation to the V˙O2sc while performing strenuous exercise.
  
  
  METHODS
  The mechanical Pb was measured in 12 recreational cyclists (24 ± 1 yr, 70.9 ± 3.9 kg) during heavy- and severe-intensity cycling. The resistive and elastic components of Pb were quantified using the modified Campbell diagram.
  
  
  RESULTS
  Total Pb significantly increased (P < 0.05) over the V˙O2sc phase during both heavy (Δ13 ± 2 J·min) and severe work rate transitions (Δ219 ± 56 J·min). The magnitude of this increase was relatively greater during severe cycling trials (P < 0.05). The greater "slow component" rise in total Pb during severe work rate transitions was consequent to relatively larger increases in the inspiratory and expiratory resistive Pb and inspiratory elastic Pb (P < 0.05).
  
  
  CONCLUSIONS
  The findings of this investigation support the thesis that the energetic contribution from respiratory muscles to the V˙O2sc amplitude is disproportionately higher during severe- compared with that during heavy-intensity exercise.
authors.affiliation: 1Heart Foundation Research Centre, Griffith Health Institute, Griffith University, Queensland, AUSTRALIA; 2Faculty of Human Movement Sciences, VU University Amsterdam, Amsterdam, THE NETHERLANDS; and 3School of Kinesiology, University of British Columbia, Vancouver, British Columbia, CANADA.
authors.forename: Troy J
authors.initials: TJ
authors.lastname: Cross
authors.forename: Caroline
authors.initials: C
authors.lastname: Winters
authors.forename: A William
authors.initials: AW
authors.lastname: Sheel
authors.forename: Surendran
authors.initials: S
authors.lastname: Sabapathy
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D008297:Male; D053580:Muscle Strength; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D015656:Respiratory Mechanics; D012132:Respiratory Muscles / Q000502:physiology*; D014797:Vital Capacity; D014939:Work of Breathing / Q000502:physiology*; D055815:Young Adult