Phosphorus-31 magnetic resonance spectroscopy (31P-MRS) is unique in its ability to study, continuously and non-invasively, the biochemical pathways for the supply and utilization of energy in muscle. The post-exercise recovery rate of skeletal muscle phosphocreatine (PCr) is a validated index of mitochondrial oxidative capacity in vivo. In a preliminary study, we measured PCr recovery kinetics following exercise, using 31P-MRS before and after initiating statin therapy and found that the return to metabolic equilibrium was longer after 4 weeks of statin therapy, suggesting mitochondrial impairment. i