Achilles tendinitis is an overuse injury of the Achilles tendon, the band of tissue that connects calf muscles at the back of the lower leg to your heel bone.

Achilles tendinitis most commonly occurs in runners who have suddenly increased the intensity or duration of their runs. It's also common in middle-aged people who play sports, such as tennis or basketball, only on the weekends.

The pain associated with Achilles tendinitis typically begins as a mild ache in the back of the leg or above the heel after running or other sports activity. Episodes of more-severe pain may occur after prolonged running, stair climbing or sprinting. You might also experience tenderness or stiffness, especially in the morning.