Tendons, or sinews, connect muscle to bone. The bones in a person's skeleton enable him or her to walk, run, jump, roll, lift, carry, drop, and do other important physical activities. Without the ability of tendons to connect the muscles and bones that are responsible for controlling these actions, it would be impossible for the body to move in the way it does. Since tendons are important for the body to move, it is important to keep them strong, healthy, and free from harm.

The composition of tendons is much like gelatin, but harder and not as elastic. They are made of special cells called tenocytes, water, and fibrous collagen proteins. Millions of these collagen proteins weave together to form the strong strand of flexible tissue called a tendon. Tendons grow into the bone and form a tough mineralized connection. This connection creates a permanent bond that is extremely tough to break.

Despite their incredible strength, tendons can be damaged if overstrained or improperly cared for. Overuse can cause the collagen fibers in the tendon to form small tears, a condition called tendonitis. Damage to tendons most often occurs in the knee, ankle, shoulder, wrist, bicep, calf, and back of the heel -- which is called the Achilles tendon.

The Achilles tendon is the most well known of the tendons. It was named after the mythological figure, Achilles, who was killed when an arrow struck him in the back of his heel. The Achilles tendon connects the heel to the back of the calf. Since it is used so frequently, it is one of the most commonly damaged tendons.

Tendons cannot easily heal from damage, which makes medical intervention necessary when one is injured. If tendons are damaged, anti-inflammatory drugs are used to bring the swelling down. Complete rest for a long period of time is generally mandatory. If tendons tear completely, surgical intervention is necessary to reconnect the tissue to the bone.

Strength training can help ensure tendons remain tough and less susceptible to damage. As a person ages, the tendons in the body also age, and excess weight and activity can slowly weaken tendons over time. Studies show gradual strength training can help keep tendons healthy and strong.