Beyond a Single Time Constant: Evaluating the Cross- Protocol Transferability of τW′ in Cyclists

Abstract

The quantification of W′ reconstitution kinetics (τ_W′) is central to W′ balance (W′_BAL) modelling, yet whether an individualized τ_W′ can be transferred across different intermittent exercise structures remains unclear. This study examined the cross-protocol transferability of a reference τW′ derived from a 60 s - 30 s high intensity interval training (HIIT) protocol. Six trained male cyclists completed baseline testing and four exhaustive HIIT protocols: 60 s–30 s HIIT, short HIIT (S-HIIT), long HIIT (L-HIIT), and decreasing power output HIIT (DPO-HIIT). The τ_W′ required to yield W′_BAL = 0 kJ at task failure during 60 s - 30 s HIIT was defined as Ref-τ_W′ and subsequently applied to the other protocols. End-exercise W′_BAL differed across protocols (p<0.001). Ref-τ_W′ produced the smallest bias and root mean square error during S-HIIT (3.3 and 4.3 kJ), whereas larger errors were observed during L-HIIT (6.5 and 7.0 kJ) and DPO-HIIT (6.8 and 7.4 kJ). Protocol-specific τ_W′ values also differed (p<0.001), with no differences between 60 s - 30 s and S-HIIT or between L-HIIT and DPO-HIIT. These findings indicate that τ_W′ is protocol dependent and that a single individualised value may not accurately transfer across distinct HIIT structures. Transferability therefore appears greater between protocols with similar work and recovery characteristics.