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

It is believed that exercise performed in the heavy intensity exercise (above Gas Exchange Threshold (GXT)) domain will reach a steady state (albeit delayed). However reported modelled time constants for the slow component indicate the VO² response would not be complete within the duration of the exercise performed. This raises important questions regarding the concept of heavy intensity exercise and the suitability of current exponential models to describe the slow component of VO². .The purpose of this study was; to comprehensively describe the relationship between exercise intensity and the slow component of VO², and to investigate whether a steady-state in VO² was achieved during constant work-rates above the gas exchange threshold (GXT). Eight recreationally active male participants volunteered for this study (age: 24±8 y; Stature: 1.78±0.09 m; mass: 76.5±10.1 kg; VO²peak: 3.89±0.72 L.min-1). The participants were required to visit the laboratory on nine occasions for testing. The first visit involved determination of GXT and VO²peak with a progressive ramp exercise test. The following tests involved multiple laboratory visits, with the participants performing a square wave transition from rest to one of eight exercise intensities; -20%Δ (minus 20% of the difference in VO² between that at GXT and VO2peak), -10%Δ, GXT, 10%Δ, 20%Δ, 30%Δ, 40%Δ and 50%Δ. The VO² response was modelled using both mono and bi exponential non-linear regression techniques. Difference in the SEE for the mono and bi exponential models were analysed using a paired samples t-test, and the slope of VO² vs Time (for the final minute of exercise) was analysed using a one-sample t-test. A slow component of VO² was found for all exercise intensities. The SEE’s were significantly lower in the bi vs. mono exponential model across all exercise intensities (p<0.05). The slope was not different from 0 (p<0.05) for the final minute of any exercise intensity, indicating that a steady-state was achieved. The modelled slow component time constants are typical of literature reported values, but would indicate that VO² would not be achieved during the duration of the exercise. These findings demonstrate that VO² was in steady-state for all exercise intensities for the final minute of exercise. These findings also demonstrate that using a bi exponential model, a slow component can be modelled even below GXT and that the time constant of the slow component would be too long to result a steady-state.