cientists found that shutting down two genes in the muscle tissue of lab rat severely limited their ability to run, two genes control the synthesis of a protein called AMPK in lab rat  skeletal muscle, the muscle that controls movement  These genes allow muscles to make energy from sugar, and if this process is disrupted, the mitochondria, which make energy in muscles, are at lower levels and the muscles do not function properly
Turning off the gene that makes the AMPK protein limits the rar's ability to run.
 So scientists think the differences between couch potatoes and Olympians may all be genetic