Purpose: The purpose of the present study was to determine whether maximal cardiac output (Q) is affected by the duration of the maximal exercise test. Methods: Nine healthy men (N = 6) and women (N = 3) performed three separate maximal treadmill exercise tests, separated by at least 24 h, and underwent a body composition assessment by hydrostatic weighing, all within a 2-wk period. A baseline maximal exercise test was performed to establish VO2max. The second and third tests, assigned randomly, were designed to elicit the subjects' predetermined VO2max in either 6 or 12 min. Heart rate (HR), blood pressure (BP), minutes of ventilation, and oxygen consumption (VO2) were measured during all tests. At the end of the 6- and 12-min tests, Q was measured using an acetylene rebreathing technique. Stroke volume (SV), mean arterial pressure (MAP), total peripheral resistance (TPR), and arteriovenous O2 difference were calculated using standard equations. Results: Repeated-measures ANOVA indicated that there were no significant differences in HR and VO2max between the baseline, 6-min, and 12-min tests. Paired t-tests revealed significantly greater Q (25.1 ± 5.6 vs 23.7 ± 5.2 L·min-1) and SV (138.3 ± 31.5 vs 130.5 ± 31.2 mL) in the 6- versus 12-min tests, respectively. There were no significant differences in systolic BP, diastolic BP, MAP, TPR, or arteriovenous O2 difference. Conclusions: Despite there being no difference in VO2max between the two tests, the 6-min maximal exercise test resulted in a significantly greater Q than the 12-min test, because of a significantly greater SV. Thus, there was a disassociation between VO2 and Q during maximal exercise.
- Acetylene rebreathing
- Exercise testing
- Stroke volume
ASJC Scopus subject areas
- Orthopedics and Sports Medicine
- Physical Therapy, Sports Therapy and Rehabilitation