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 (τ) of oxygen uptake (V̇ O2 ) during moderate‐ and heavy‐intensity exercise, and the slow component of V̇ O2 during heavy‐intensity exercise using previously published exponential models. Estimates for τ and the slow component were different (P < 0.05) among models. For moderate‐intensity exercise, a two‐component exponential model, or a mono‐exponential model fitted from 20 s to 3 min were best. For heavy‐intensity exercise, a three‐component model fitted throughout the entire 6 min bout of exercise, or a two‐component model fitted from 20 s were best. When the time delays for the two‐ and three‐component models were equal the best statistical fit was obtained; however, this model produced an inappropriately low ΔV̇ O2 /ΔWR (WR, work rate) for the projected phase 2 steady state, and the estimate of phase 2 τ was shortened compared with other models. The slow component was quantified as the difference between V̇ O2 at end‐exercise (6 min) and at 3 min (ΔV̇ 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 ∼2 min (vs. arbitrary 3 min). Using this delay ΔV̇ O2 (6‐2 min) was ∼400 ml min −1 . Use of valid consistent methods to estimate τ and the slow component in exercise are needed to advance physiological understanding.