A detailed comparison of oxygen uptake kinetics at a range of exercise intensities

Aim: The aim of this study was to comprehensively examine oxygen uptake (VO2) kinetics during cycling through mathematical modeling of the breath-by-breath gas exchange responses across eight conditions of unloaded cycling to moderate to high-intensity exercise. Methods: Following determination of GET and V O2peak, eight participants (age: 24±8y; height: 1.78±0.09m; mass: 76.5±10.1kg; V O2peak: 3.89±0.72 L.min-1) completed a series of square-wave rest-to-exercise transitions at; -20%∆ (GET minus 20% of the difference in V O2 between that at GET and VO2peak), -10%∆, GET, 10%∆, 20%∆, 30%∆, 40%∆, and 50%∆. The V O2 kinetic response was modelled using mono- and bi-exponential non-linear regression techniques. The difference in the standard error of the estimates (SEE) for the mono- and bi-exponential models, and the slope of V O2 vs time (for the final minute of exercise) were analysed using paired and one-sample t-tests, respectively. Results: The bi-exponential model SEE was lower than the mono-exponential model across all exercise intensities (p0.05). The modelled slow component time constants, typical of literature reported values, indicated that the V O2 kinetic response would not be completed during the duration of the exercise. Conclusion: It was shown that the addition of the more complex bi-exponential model resulted in a better model fit across all intensities (notably including sub-GET intensities). The slow component phase was incomplete in all cases, even when the investigation of slopes indicated that a steady state had been achieved.