W' reconstitution modelling during intermittent exercise performed to task failure

W' balance (W'_BAL) modelling is becoming an important tool to monitor intermittent cycling performance. This study assessed the ability of different time constant (τ_W') equations for W' reconstitution (W'_rec) to predict exhaustion during intermittent exercise and the relationship between parameters of W'_rec with established determinants of endurance performance.

Thirteen cyclists performed cycling performance tests to determine: lactate threshold (LT), critical power (CP), W', V̇O_2max, maximal aerobic power (MAP) and maximal sprint power (P_max). Participants subsequently performed three intermittent W' depletion trials to volitional exhaustion involving different work and recovery periods: 20:10; 3 × 20 s intervals separated by 10 s recoveries before a final continuous effort, 60:30; 3 × 60 s intervals separated by 30 s recoveries before a final continuous effort, 20:10_TE; repeated 20 s intervals each separated by 10 s recoveries. W'_BAL was determined via five different τ_W' equations and an individualised equation (τ_W'INDV) calculated from the 20:10_TE under the assumption that the point of task failure represents 0 kJ.

Current τ_W' equations failed to predict exhaustion during intermittent exercise protocols to exhaustion. Total work done above CP for the 20:10_TE (W'_total20:10_TE) was positively correlated with absolute and relative LT, CP, V̇O_2max, MAP, and P_max (r = 0.64-0.80; P < 0.05). The τ_W'INDV was negatively correlated with relative CP (r = - 0.69), and LT₁ (r = - 0.58), and W'_total20:10_TE (r = - 0.63).

Individualised τ_W' should be utilised for the accurate prediction of W'_BAL. W'_rec is influenced primarily by aerobic performance parameters, including LT₁ and CP.