Figure 1.

Changes with age in whole-body VO₂ peak (A), skeletal muscle citrate synthase activity (B), mtDNA copy number in skeletal muscle (C) and blood (D), protein levels of total oxidative phosphorylation muscle proteins (E) PGC-1α expression (F), cytochrome c oxidase protein content (G), and activity (H). These data show significant correlation of age to oxidative capacity measured at the level of the whole-body (beta = −3.225; p < 0.001) and skeletal muscle (beta = 0.536; p < 0.001). There was significant correlation of age with muscle mtDNA (beta = −0.095; p = 0.009), but not with blood mtDNA (beta = 0.088; p = 0.54). Skeletal muscle expression levels of oxidative phosphorylation proteins were significantly correlated to age (beta = −1.153; p = 0.013) but not that of PGC-1α protein levels and age (beta = −0.063; p = 0.39). Beta represents the estimated change in each measurement per 10-year increase in age and is estimated from a hierarchal linear model with a random intercept for each family unit.