A comparison of modelling techniques used to characterise oxygen uptake kinetics during the on-transient of exercise

We compared estimates for the phase 2 time constant (tau) of oxygen uptake (V(over dot)(O2)) during moderate- and heavy-intensity exercise, and the slow component of V(over dot)(O2) during heavy-Intensity exercise using previously published exponential models. Estimates for tau and the slow component were different (P < 0.05) among models. For moderate-intensity exercise, a twocomponent exponential model, or a mono-exponential model fitted from 20 s to 3 min were best. For heavy-intensity exercise, a three-cornponent model fitted throughout the entire 6 min bout of exercise, or a two-component model Etted from 20 s were best. When the time delays for the two- and three-component modelswere equal the best statistical fit was obtained; however, this model produced an inappropriately low DeltaV(over dot)(O2)/Delta WR, (WR, work rate) for the projected phase 2 steady state, and the estimate of phase 2 tau was shortened compared with other models. The slow component was quantified as the difference between V(over dot)(O2) at end-exercise (6 min) and at 3 min (DeltaV(over dot)(O2(6-3 min)); 259 ml min(-1)), and also using the phase 3 amplitude terms (truncated to end-exercise) from exponential fits (409-833 ml min(-1)). Onset of the slow component was identified by the phase 3 time delay parameter as being of delayed onset similar to2 min (vs. arbitrary 3 min). Using this delay DeltaV(over dot)(O2(6-2 min)) was similar to 400 ml min(-1). Use of valid consistent methods to estimate tau and the slow component in exercise are needed to advance physiological understanding.