The influence of sex, hemoglobin mass, and skeletal muscle characteristics on cycling critical power


Critical power (CP) represents an important threshold for exercise performance and fatiguability. We sought to determine the extent to which sex, hemoglobin mass (Hbmass), and skeletal muscle characteristics influence CP. Prior to CP determination (i.e., 3-5 constant work rate trials to task failure), Hbmass and skeletal muscle oxidative capacity (τ) were measured and vastus lateralis muscle biopsy samples were collected from 12 females and 12 males matched for aerobic fitness relative to fat-free mass (mean (SD); V̇O2max: 59.2 (7.7) vs. 59.5 (7.1) mL·kg FFM-1·min-1, respectively). Males had a significantly greater CP than females in absolute units (225 (28) vs. 170 (43) W; p=0.001) but not relative to body mass (3.0 (0.6) vs. 2.7 (0.6) W·kg BM-1; p=0.267) or FFM (3.6 (0.7) vs. 3.7 (0.8) W·kg FFM-1; p=0.622). Males had significantly greater W′ (p ≤ 0.030) and greater Hbmass (p ≤ 0.016) than females, regardless of the normalization approach; however, there were no differences in mitochondrial protein content (p=0.375), τ (p=0.603), or MHC I proportionality (p=0.574) between males and females. Whether it was expressed in absolute or relative units, CP was positively correlated with Hbmass (0.444≤r≤0.695; ptextless0.05), mitochondrial protein content (0.413≤r≤0.708; ptextless0.05), and MHC I proportionality (0.506≤r≤0.585; ptextless0.05), and negatively correlated with τ when expressed in relative units only (-0.588≤r≤-0.527; ptextless0.05). Overall, CP was independent of sex but variability in CP was related to Hbmass and skeletal muscle characteristics. The extent to which manipulations in these physiological parameters influence CP warrants further investigation to better understand factors underpinning CP.

Journal of Applied Physiology