Difference in Physiological Components of VO2 Max During Incremental and Constant Exercise Protocols for the Cardiopulmonary Exercise Test

[Purpose] VO2 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, VO2 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] VO2 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 VO2 value, the VO2 in incremental exercise would have a higher ratio of cardiac output than constant exercise, and VO2 in constant exercise would have a higher ratio of O-2 extraction than incremental exercise at the end of exercise.