Based on observation of professional athletes, certain principles have been evolved empirically which have been found to help maintain and increase function and, to some extent, to counteract the effects of aging. These principles are:
1. Repetition to the point of exhaustion of a muscle, if done against a fixed load, will result in stretching of ligaments and joint instability, especially in the knee. Any exercise doing this should be avoided.
2. Exercise against resistance which is fixed or exercise through a limited range of motion will result in functional shortening of the muscle and limitation of its usefulness for athletic endeavor.
3. When exercise is performed, the joint must carry out a full range of motion to achieve maximum athletic function.
4. The load or resistance should increase as the mechanical advantage of the muscle increases in association with movement of the joint.
5. Enduring athletic ability depends on maintaining in all joints the full range of joint motion peculiar to a particular athlete.
6. Endurance is best achieved and maintained by repetitious motion against light resistance.
7. There are specific anatomical areas and ranges of motion peculiar to various sports and various activities in those sports. The standard for each athlete is an individual one.