For tissue to increase in strength and efficiency, it must be subjected to a force that exceeds its normal capability, or overload. Adaptation of tissue to overload results in the training effect. If, however, the force acting on tissue is too great or is applied too often, the tissue fails to repair and adapt. In adult recreational athletes, overuse injuries usually develop after an average of 2 years of regular training, during which workouts usually increase in duration and intensity. The muscle-tendon unit is the most common site of overuse injury.
Bone is the second most frequent site.
When bone is overused, a stress fracture results. Less common are overuse injuries to ligaments and joints. Since the muscle-tendon unit is the site most often affected, I have limited my remarks to this injury. Overuse injury of a muscle. Rather, the process becomes one of focal degeneration within the tendon, the possible cause of which is relative tissue hypoxia.