The Principle of Use or Disuse implies that your exercise gains will go away when you do not maintain them. This means that you become deconditioned and muscles atrophy when not in use. Muscle strength tends to go at about 1/8 of starting strength per week, with larger and stronger fast twitch muscle fibers decreasing faster than slow twitch fibers. Over time muscles become shorter and less limber with disuse. When we move gravity forces our muscles to contract and pump blood back to our hearts and it’s easier to breath since our postures tend to be better when exercising. Exercise stimulates our metabolism, the formation of new bone cells, glucose tolerance and an overall sense of well being. So enjoy every step, rep, set, lap or mile. Know that it’s worth every minute.