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INTRODUCTION: Changes in the parameters of the power-time relationship (critical power (CP) and W') during endurance exercise would have important implications for performance. We tested the hypotheses that CP and W', estimated using the end-test power (EP) and the work done above EP (WEP), respectively, during a the 3-min all-out test (3MT), can be reliably determined, and would be lower, after completing 2 h of heavy-intensity exercise. METHODS: In study 1, six cyclists completed a 3MT immediately after 2 h of heavy-intensity exercise on two occasions to establish the reliability of EP and WEP. In study 2, nine cyclists completed a control 3MT, and a fatigued 3MT and constant power output tests to 30 min or the limit of tolerance (Tlim) below and above F-EP after 2 h of heavy-intensity exercise. RESULTS: In study 1, EP (273 ± 52 vs 276 ± 58 W) and WEP (12.4 ± 4.3 vs 12.8 ± 4.3 kJ) after 2 h of heavy-intensity exercise were not different (P > 0.05) and were highly correlated (r = 0.99; P F-EP and Tlim was shorter than 30 min during exercise <F-EP (18.2 ± 10.7 min). CONCLUSIONS: The EP and WEP may be reliably determined after 2-h heavy-intensity exercise. The 8% and 20% reductions in EP and WEP, respectively, have important implications for performance during endurance exercise. The physiological characterization of EP (and, by extension, CP) may differ in a fatigued compared with a rested state.
Clark et al. (Fri,) studied this question.