“The explanation may be that gene activity in our muscles changes when the muscles don’t contract for long periods of time. In one experiment, researchers at the University of Massachusetts asked a group of healthy young men to walk around using crutches such that the muscles in their left legs never contracted. After only two days of inactivity, the scientists biopsied muscles in both legs. In the left leg, the DNA repair mechanism had been disrupted, insulin response was dropping, oxidative stress was rising, and metabolic activity within individual muscle cells was slowing.”