title: Attenuated relationship between cardiac output and oxygen uptake during high-intensity exercise.
abstract: OBJECTIVE
  Recent findings have challenged the belief that the cardiac output (CO) and oxygen consumption (VO(2) ) relationship is linear from rest to maximal exercise. The purpose of this study was to determine the CO and stroke volume (SV) response to a range of exercise intensities, 40-100% of VO(2max), during cycling.
  
  
  METHODS
  Ten well-trained cyclists performed a series of discontinuous exercise bouts to determine the CO and SV vs. VO(2) responses.
  
  
  RESULTS
  The rate of increase in CO, relative to VO(2) , during exercise from 40 to 70% of VO(2max) was 4.4 ± 1.4 L L(-1). During exercise at 70-100% of VO(2max) , the rate of increase in CO was reduced to 2.1 ± 0.9 L L(-1) (P = 0.01). Stroke volume during exercise at 80-100% of VO(2max) was reduced by 7% when compared to exercise at 50-70% of VO(2max) (134 ± 5 vs. 143 ± 5 mL per beat, P = 0.02). Whole body arterial-venous O(2) difference increased significantly as intensity increased.
  
  
  CONCLUSIONS
  The observation that the rate of increase in CO is reduced as exercise intensity increases suggests that cardiovascular performance displays signs of compromised function before maximal VO(2) is reached.
authors.affiliation: Human Performance Laboratory, Department of Kinesiology and Health Education, The University of Texas at Austin, USA. joel.trinity@utah.edu
authors.forename: J D
authors.initials: JD
authors.lastname: Trinity
authors.forename: J F
authors.initials: JF
authors.lastname: Lee
authors.forename: M D
authors.initials: MD
authors.lastname: Pahnke
authors.forename: K C
authors.initials: KC
authors.lastname: Beck
authors.forename: E F
authors.initials: EF
authors.lastname: Coyle
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001642:Bicycling; D002302:Cardiac Output; D015444:Exercise; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption; D012123:Pulmonary Ventilation; D013997:Time Factors; D055815:Young Adult