Chest
Clinical InvestigationsCan Maximal Cardiopulmonary Capacity be Recognized by a Plateau in Oxygen Uptake?
Section snippets
Methods
Five healthy male subjects and one healthy female subject (mean [±SD] age, 33±6 years) participated in the study. None was taking any medication or had any remarkable medical history. All had at least average fitness; the mean (±SD) maximal oxygen uptake was 50.0±12 ml O2/kg/min.
Results
Differences between measurements made on day 1 and day 2 of heart rate, gas exchange, and perceptual responses are presented in Table 1. The slope of the change in oxygen uptake for subject 1 on day 1 and day 2 are illustrated in Figures 2 and 3, respectively.
The mean maximal oxygen uptake of the subjects was 50.0±11.7 ml/kg/min on day 1 and 49.6±11 ml/kg/min on day 2. This difference was not significant (NS). Accordingly, treadmill time was not different between day 1 (9.0±1.4 minutes) and day
Discussion
An important observation made from the present data was the variability in the slope of the change in oxygen uptake throughout progressive exercise, despite a constant, consistent change in external work and the use of large, averaged samples. A slope, in the present context, is defined as the change in oxygen uptake for a given sample associated with a unit change in external work. Thus, a slope not different from zero at peak exercise suggests that oxygen uptake was not increasing
Conclusion
Intuitively, the body's cardiorespiratory and metabolic systems must reach some finite limit beyond which oxygen uptake can no longer be increased. The factors that limit exercise capacity are not entirely clear, however, exercise capacity depends on disease, fitness, and the type and duration of exercise. The traditional interpretation of the plateau concept assumes oxygen delivery always limits exercise capacity. However, this may not be the case under all conditions.1 This may explain the
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Manuscript received February 16; revision accepted June 12.