Bi-exponential modelling of [Formula: see text] reconstitution kinetics in trained cyclists

PURPOSE: The aim of this study was to investigate the individual [Formula: see text] reconstitution kinetics of trained cyclists following repeated bouts of incremental ramp exercise, and to determine an optimal mathematical model to describe [Formula: see text] reconstitution. METHODS: Ten trained cyclists (age 41 ± 10 years; mass 73.4 ± 9.9 kg; [Formula: see text] 58.6 ± 7.1 mL kg min(−1)) completed three incremental ramps (20 W min(−1)) to the limit of tolerance with varying recovery durations (15–360 s) on 5–9 occasions. [Formula: see text] reconstitution was measured following the first and second recovery periods against which mono-exponential and bi-exponential models were compared with adjusted R(2) and bias-corrected Akaike information criterion (AICc). RESULTS: A bi-exponential model outperformed the mono-exponential model of [Formula: see text] reconstitution (AICc 30.2 versus 72.2), fitting group mean data well (adjR(2) = 0.999) for the first recovery when optimised with parameters of fast component (FC) amplitude = 50.67%; slow component (SC) amplitude = 49.33%; time constant (τ)(FC) = 21.5 s; τ(SC) = 388 s. Following the second recovery, W′ reconstitution reduced by 9.1 ± 7.3%, at 180 s and 8.2 ± 9.8% at 240 s resulting in an increase in the modelled τ(SC) to 716 s with τ(FC) unchanged. Individual bi-exponential models also fit well (adjR(2) = 0.978 ± 0.017) with large individual parameter variations (FC amplitude 47.7 ± 17.8%; first recovery: (τ)(FC) = 22.0 ± 11.8 s; (τ)(SC) = 377 ± 100 s; second recovery: (τ)(FC) = 16.3.0 ± 6.6 s; (τ)(SC) = 549 ± 226 s). CONCLUSIONS: W′ reconstitution kinetics were best described by a bi-exponential model consisting of distinct fast and slow phases. The amplitudes of the FC and SC remained unchanged with repeated bouts, with a slowing of W′ reconstitution confined to an increase in the time constant of the slow component.