Utility of the Respiratory Compensation Point for Estimating Critical Power: Insights From Normoxia and Hypoxia

Abstract

We examined the validity of the respiratory compensation point (RCP) in estimating critical power (CP) by determining the relative agreement between them following an acute intervention, hypoxia, which reduces RCP and CP. RCP and CP were determined in normoxia (N: FiO2 = 0.21) and hypoxia (H: FiO2 = 0.13) with RCP converted to a power output (W) via linear regression of the V̇O2–time relationship with correction for the mean response time. RCP and CP were lower in hypoxia compared to normoxia (p < 0.001), but there was no difference between CP and RCP in N or H (N: 174 ± 26 (CP) vs. 178 ± 30 (RCP) W; H: 133 ± 19 (CP) vs. 139 ± 22 (RCP) W, p = 0.53). In both N (r = 0.32, p = 0.31) and H (r = 0.00, p = 0.99), RCP was not correlated with CP. Moreover, the 95% limits of agreement (LOA) were unacceptably wide (N: 3 ± 64 W; H: 7 ± 57 W). There was no correlation between the change in RCP and the change in CP caused by hypoxia (W: r = 0.32), with similarly poor 95% LOA (W: −3 ± 62 W). The weak correlations and wide LOA within and between conditions suggest little practical values in using RCP to estimate CP.