(A, B) Agonists to melanocortin receptors 4 and 5 (MC4R, MC5R) microinjected into the paraventricular nucleus of the hypothalamus (PVN) induced significant increases in short-term (3h) daytime physical activity levels in rats. No differences were found between high-capacity runners (HCR) and low-capacity runners (LCR). (C, D) Antagonists to MC4R and MC5R in the PVN did not suppress nighttime (12h) physical activity levels in either HCR or LCR. N= 6–9 per group, data represent mean plus SEM, *significant change from vehicle, **HCR>LCR within treatment (p<0.05).