Comparison of the critical power estimated by the best fit method and the maximal lactate steady state; [Comparaison entre la puissance critique estimée par la méthode bien-être et l’état d’équilibre maximal du lactate]

Aims: Maximal lactate steady state (MLSS) is accepted as the gold standard method to determine the upper boundary of heavy exercise domain, while critical power (CP) is one of the most practical ways to estimate the lower boundary of severe exercise domain. However, it has been recently discussed that the upper boundary of heavy-intensity exercise domain does not equal to lower boundary of severe-intensity exercise domain. Conversely, the best individual fit method (CPfit) has recently been suggested as an accurate estimation of CP. However, there has not been a comparative evaluation of CPfit versus MLSS. The aim of this study was, therefore, to focus on the comparison of CPfit with MLSS. Methods: Eleven well-trained male cyclists participated in this study. Following the determination of maximal oxygen uptake, MLSS was determined through the performance of standard 30-minute constant work rate exercises performed on separate days. Cyclists performed four constant-load exercises lasting 2–15 minutes on different days. The data were then fitted to mathematical models to obtain CPfit. Bland-Altman plot with 95% limits of agreement (LoA) was used to measure agreement between CPfit and MLSS. Results: According to the findings, CPfit overestimated the work rate corresponding to MLSS (300 ± 38 W vs. 265 ± 39 W; P = 0.001; effect size = 3.28). Bland-Altman results showed high LoA (14 to 55.9 W) and very high bias (bias = 35 ± 10.7 W; P = 0.001; r: 0.96) between CPfit and MLSS. Conclusion: CPfit was not identical for MLSS.