The Achilles tendon is the largest and strongest tendon in the human body. Connecting the calf muscles to the heel, your Achilles tendon is what allows you to push off the ball of your foot when engaged in physical activity. It is a thick, elastic, and fibrous band of tissue that is able to withstand great force. The immense and repetitive force that it is subject to during athletic activity also makes it vulnerable to injury. With repetitive stress and overuse, the Achilles can undergo micro tearing of the fibers which leads to structural changes including thickening and hardening of the tendon. This weakens the tendon and makes it less elastic causing irritating pain and inflammation known as tendonitis.