title: Non-linear relationships between central cardiovascular variables and VO2 during incremental cycling exercise in endurance-trained individuals.
abstract: OBJECTIVE
  The purpose of this study was to examine the relationships between the central cardiovascular variables (cardiac output, stroke volume and heart rate) and oxygen uptake (VO2) during continuous, incremental cycle exercise to maximal aerobic capacity (VO2max).
  
  
  METHODS
  Twenty-one moderately to highly trained males (n=19) and females (n=2) participated in the study. A baseline maximal exercise test was performed to measure VO2max. Following the initial VO2max test, cardiac output was measured (CO2 rebreathing technique) at rest and 3 times during each of 4 exercise trials (2 submaximal tests to 90% VO2max and 2 maximal tests). Stroke volume and arteriovenous O2 difference were calculated using standard equations.
  
  
  RESULTS
  Significant non-linear relationships were found between all central cardiovascular variables and VO2 (P<0.01). A plateau in cardiac output at VO2max was identified in 3 subjects. Stroke volume plateaued at an average of 37+/-12.5% of VO2max in 18 subjects and increased continuously to VO2max in 3 subjects. The arteriovenous O2 difference progressively increased to VO2max in 17 subjects and revealed a plateau response in 4 subjects.
  
  
  CONCLUSIONS
  Our data suggest that there is a significant non-linear relationship between the central cardiovascular variables and VO2 during incremental exercise to VO2max. Furthermore, depending on the person, VO2max may be limited by cardiac output (evidence of cardiac output[Q] plateau) or peripheral factors (continued increase in Q).
authors.affiliation: Exercise Physiology Laboratories, The University of New Mexico, Albuquerque, NM, USA. cvella@utep.edu
authors.forename: C A
authors.initials: CA
authors.lastname: Vella
authors.forename: R A
authors.initials: RA
authors.lastname: Robergs
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D017711:Nonlinear Dynamics; D010101:Oxygen Consumption / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D011446:Prospective Studies