All hard work done to get up to the point of being in shape and then you take a break off and stop and go back to your old ways is called reversibility because it'll then be as if you never worked out in the first place.
Principle of Reversibility is the decline of skill and fitness level due to taking a break from exercise or being inactive.
It is called such because all the result of hardwork and labor done to achieve and maintain one's skill and fitness level will be reversed because said fitness regime is not maintained; making the body lax, eventually declining in skill performance and fitness level.
