Fig. 3. Transcriptional basis of the tuning of oxidative capacity by endurance training. (A) Normalized maximal (V_O2_max) consumption, mitchondrial volume and mitochondrial RNA levels of various respiratory proteins in m. vastus lateralis of endurance runners vs untrained subjects. mRNA levels are relative to levels of 28S rRNA. (B) Differences in concentration of transcripts in tibialis anterior muscle between untrained and endurance-trained subjects relative to 18S rRNA. Values are means ± s.e.m. Black boxes denote those mRNAs being encoded by mitochondrial DNA. Trained subjects had been exposed to years of endurance training and competition. Significant differences between values from endurance-trained vs untrained subjects are indicated: *P<0.05; P<0.10. For enzymes, see List of abbreviations.