Difference in Physiological Components of VO(2 Max) During Incremental and Constant Exercise Protocols for the Cardiopulmonary Exercise Test

[Purpose] VO(2) is expressed as the product of cardiac output and O(2) extraction by the Fick equation. During the incremental exercise test and constant high-intensity exercise test, VO(2) results in the attainment of maximal O(2) uptake at exhaustion. However, the differences in the physiological components, cardiac output and muscle O(2) extraction, have not been fully elucidated. We tested the hypothesis that constant exercise would result in higher O(2) extraction than incremental exercise at exhaustion. [Subjects] Twenty-five subjects performed incremental exercise and constant exercise at 80% of their peak work rate. [Methods] Ventilatory, cardiovascular, and muscle oxygenation responses were measured using a gas analyzer, Finapres, and near-infrared spectroscopy, respectively. [Results] VO(2) was not significantly different between the incremental exercise and constant exercise. However, cardiac output and muscle O(2) saturation were significantly lower for the constant exercise than the incremental exercise at the end of exercise. [Conclusion] These findings indicate that if both tests produce a similar VO(2) value, the VO(2) in incremental exercise would have a higher ratio of cardiac output than constant exercise, and VO(2) in constant exercise would have a higher ratio of O(2) extraction than incremental exercise at the end of exercise.