Overuse injuries are generally caused by repeated microscopic injuries to the musculo-skeletal system. Tissues can withstand great loads but there is a critical limit to this capacity, which varies greatly between individuals.

There are many intrinsic and extrinsic factors that make tissues susceptible to injury:

Intrinsic. - Such as malalignment of the leg, muscle imbalance and other anatomical factors.

Extrinsic - Such as training errors, faulty technique, incorrect equipment and surfaces, poor conditions.

In adults, overuse injuries are more prevalent after 2 years of regular daily training. With reference to the type of sport involved, 80 percent of overuse injuries occur in endurance sports, such as long distance running, or individual one man sports that require skilled technique and repetitive movements, such as tennis, gymnastics, and weight-lifting.

About 80 percent of these injuries occurred at the lower extremities of the body, most frequently at the knee (28 percent) and the ankle, foot and heel (21 percent).

Inflammation represents the body's response to tissue injury caused by pressure, friction, repeated load or overload and external trauma. Trauma is associated with some degree of bleeding, which in turn causes swelling and increased pressure. Both extrinsic and intrinsic factors contribute to the inflammatory reaction in tendons, tendon and muscle attachments, bursae and the periosteum. Common combinations of frequency and loading causing overuse injuries, are:

• normal load at high frequency
• heavy load at normal frequency
• heavy load at high frequency

Whatever the nature of the underlying cause, the inflammatory response leads to impaired and painful mobility of the affected part and so enforces rest. If it affects gliding surfaces, such as those of tendons and their sheaths, crepitus or 'creaking' might develop. If inflammation goes unchecked, scar tissue will develop and, for this reason, early intensive treatment is recommended.