The slow component of VO2 kinetics in very heavy and fatiguing square-wave exercise

We hypothesized that oxygen consumption (VO2) rises incrementally in very heavy and fatiguing exercise where the slow component gain increases with higher work rates. Fight trained males completed a graded exercise test and bouts of square-wave cycle ergometry at 40% and 60% of the difference between the estimated lactate threshold (LT) and VO2peak (designated 40%D and 60%D). Exhaled gases were collected and analyzed every breath using models that allowed for a linear slow component or a slow component with one or more exponential increments. All subjects were able to complete 30 min at 40%D but not at 60%D. The slow component was generally best fit with two increments at 40%D and two or three increments at 60%D. In further, our results question the reliability of determining parameters of multiple slow component increments when repeated bouts are averaged together. This study demonstrates that VO2 can continue to rise incrementally beyond the onset of the slow component in very heavy and fatiguing exercise. These results support the concept of a recurring mechanism underlying the slow component Of VO2 kinetics during square-wave exercise and suggest that the dynamics (time of onset, rate of development, magnitude) of this mechanism may vary from day to day.