1. Overload-refers to the observation that the body must be exercised at a level beyond which it is accustomed in order for training effect to occur. The system or tissue gradually adapts to this overload. The typical variables that constitute the overload include the intensity, duration and frequency of exercise.
2. Reversibility-The corollary of the overload principle,the principle of reversibility simply indicates that the gains are quickly lost when the overload is removed.
3. Specificity- training effect is specific and limited to the muscle fibers involved in the activity. In addition, the muscle fibers adapts specifically to to the type of activity: mitochondrial and capillary adaptation to endurance training, and contractile protein adaptation to resistive weight training.