A, Venn diagrams illustrating the overlap in number of exercise-responsive genes in gastrocnemius muscle between WT and ERRα-KO mice. B, The number of exercise-responsive genes associated with various biological processes identified by IPA are shown for WT and ERRα-KO gastrocnemius. *P < .05. C–E, qRT-PCR analysis of genes identified in B. Data are normalized to Rplp0 levels and expressed as means ± SEM. *, P < .05 by unpaired t test. F, CD31 staining and quantification of WT and ERRα-null gastrocnemius cross-sections. *, P < .05 by unpaired t test.