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

Abstract

The aim of this study was to comprehensively examine oxygen uptake (V O 2) 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 O 2peak , eight participants (age: 24±8y; height: 1.78±0.09m; mass: 76.5±10.1kg; V O 2peak : 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 O 2 between that at GET and VO 2peak),-10%∆, GET, 10%∆, 20%∆, 30%∆, 40%∆, and 50%∆. The V O 2 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 O 2 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 monoexponential model across all exercise intensities (p<0.05), indicating a better model fit. Steady-state V O 2 was achieved across all exercise intensities (all V O 2 vs. time slopes; p>0.05). The modelled slow component time constants, typical of literature reported values, indicated that the V O 2 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.