The clinical practices of the future depend upon the experimental findings of today. Because of the uniqueness of connective tissue, animal experimentation will be essential for advances in this field. During the last decade, the improvements in technology and the increased interest of basic scientists and research clinicians on the effects of physical activity has markedly enhanced the amount of information available to practicing physicians. Studies spanning the appearances of structure to the changes in the crosslinks of collagen, clearly demonstrate that limb immobilization (inactivity) is deleterious to all structures involved whether evaluated anatomically, physiologically, or biomechanically. Furthermore, when surgical repair is included, there are stages when the deleterious processes become accelerated with or without immobilization. Hence, clinical immobilization must be utilized in a prudent and careful manner. There is sufficient experimental evidence for clinicians to utilize motion and mechanical stimuli as a means to improve the structure and function of tendons, ligaments, and joints. However, the unresolved issues are the mode, time of initiation, or the intensity of application. Even when used with repair, recovery of normal structures and function is protracted. The primary or secondary mechanisms associated with these effects of physical activity are unknown and virtually uninvestigated at the present time.
