Training effects are not permanent. The motor system adapts to the level (overload) and type (specificity) of stress that is imposed on it. If the stress is removed, and training ceases, the motor system will again adapt to the new, now lower, level of stress, and detraining will occur. This transient nature of training adaptation is known as the reversibility principle (Thorstensson, 1977; Enoka, 1994)