Rate of utilization of a given fraction of W′ (the curvature constant of the power–duration relationship) does not affect fatigue during severe-intensity exercise

What is the central question of this study? Does the rate of utilization of W’ (the curvature constant of the power–duration relationship) affect fatigue during severe-intensity exercise? What is the main finding and its importance? The magnitude of fatigue after two severe-intensity exercises designed to deplete the same fraction of W’ (70%) at two different rates of utilization (fast versus slow) was similar after both exercises. Moreover, the magnitude of fatigue was related to critical power (CP), supporting the contention that CP is a key determinant in fatigue development during high-intensity exercise. Thus, the CP model is a suitable approach to investigate fatigue mechanisms during high-intensity exercise. The depletion of W’ (the curvature constant of the power–duration relationship) seems to contribute to fatigue during severe-intensity exercise. Therefore, the aim of this study was to determine the effect of a fast versus a slow rate of utilization of W' on the occurrence of fatigue within the severe-intensity domain. Fifteen healthy male subjects performed tests to determine the critical power, W' and peak torque in the control condition (TCON) and immediately after two fatiguing work rates (THREE and TEN) set to deplete 70% W’ in either 3 (TTHREE) or 10 min (TTEN). The TTHREE and TTEN were significantly reduced (F = 19.68, P = 0.01) in comparison to TCON. However, the magnitude of reduction in peak torque (TTHREE = −19.8 ± 10.1% versus TTEN = −16.8 ± 13.3%) was the same in the two fatiguing exercises (t = −0.76, P = 0.46). There was a significant inverse relationship between the critical power and the reduction in peak torque during both THREE (t = −0.49, P = 0.03) and TEN (t = −0.62, P = 0.02). In contrast, the W was not significantly correlated with the reduction in peak torque during both THREE (t = −0.14, P = 0.33) and TEN (t = −0.30, P = 0.10). Thus, fatigue following severe-intensity exercises performed at different rates of utilization of W’ was similar when the same work was done above the critical power (i.e. same amount of W’ used)