RNA was extracted from the left ventricle of the heart, taken from a single 15 week old inbred rat that was maintained under specific pathogen free conditions. Target cRNA was prepared using the Enzo Bioarray High Yield RNA Transcript Labeling Kit (Enzo Diagnostics, Farmingdale, NY), purified on a column (Rneasy mini kit, Qiagen), and hybridized to commercially available Affymetrix rat GeneChips arrays according to protocols recommended by the manufacturers. Data was analyzed using the GeneChip Expression Analysis Software (Affymetrix). Keywords = quantitative real-time RT-PCR Keywords = insulin receptor substrate 2 (Irs2) Keywords = phosphatidylinositol 3-kinase Keywords = regulatory subunit 1 Keywords = (Pik3r1) Keywords = endurance running Keywords = treadmill running