Original W′‐balance models do not transfer to high‐intensity interval training in trained adult runners: Proposal of a single‐coefficient linear alternative

Abstract

This study evaluated the off‐the‐shelf predictive accuracy of four original W′‐balance recovery models (Morton and Billat linear, W′ _BAL‐INT , W′ _BAL‐ODE and W′ _BAL‐CAEN ) and proposed a single‐coefficient modified linear formulation (Linear _{_mod} ) for predicting high‐intensity interval training (HIIT) performance with passive recovery in trained runners. Twenty‐seven trained runners completed a 9/3‐min running critical power (CP) test and two open‐ended HIIT sessions to volitional exhaustion at 108% CP with a 2:1 work: rest ratio. Work intervals were individualized so that energy expenditure above CP equalled 40% (HIIT40%) or 60% (HIIT60%) of W′. The original models were applied using their published parameters. All substantially over‐predicted the number of intervals completed (pooled MAE 26.4–72.4 intervals; bias +20.1 to +72.4). Linear _{_mod} with its default recovery coefficient ( R  = 1) achieved a MAE of 4.85 intervals. Optimizing R at the population level ( R  = 1.63) reduced MAE to 2.85 intervals, while athlete‐specific optimisation ( R  = 1.54 ± 0.29) reduced MAE to 0.55 intervals. Individual R values were stable between protocols (within‐subject CV = 9.9%). Original W′‐balance models did not accurately predict running HIIT performance, whereas Linear _{_mod} provided high predictive accuracy using a single athlete‐specific recovery coefficient.