The Achilles tendon is the connection between the heel and the most powerful muscle group in the body. This has long been known as a site which is prone to disabling injury. Forces up to 12 times body weight (9kN) may arise during sprinting.

The tendon can swell and may cause pain. This condition is common in athletes, runners and patients who have calf tightness. Achilles tendinitis may occur in the middle of the tendon. This is known as mid-substance Achilles Tendinitis. It may also occur at the point where the tendon connects to the heel bone.