Principle of Disuse (Reversibility / "Use It or Lose It")

"Use it or lose it" is true of any exercise program. Even among trained athletes, the beneficial effects of years of prior training are reversible when training stops for a season. For this reason, it is highly recommended that a strength athlete begin a reconditioning program of several weeks to offset the loss of strength during the lay-off period.

This is the conceptual counterpart of the overload principle: just as overloading raises the strength threshold, underloading or disuse lowers it. The physiological wasting that accompanies disuse — muscle atrophy — is covered as a physiology topic (see muscle-atrophy): atrophy is the wasting away or decrease in the size of muscle tissue from lack of use or through immobilization.

• "Use it or lose it" — training benefits are reversible.
• Even years of prior training reverse when training stops for a season.
• A several-week reconditioning program is recommended to offset strength loss after a lay-off.
• Underloading/disuse lowers the strength threshold (mirror image of overload).

• progressive-overload — disuse is the reverse: the threshold drops when load is removed.
• rebuilding-time — an over-long rest period shades into reversibility/detraining.
• muscle-atrophy — the physiological mechanism (wasting from lack of use/immobilization).
• frequency — sufficient training frequency prevents reversibility.