Muscles are attached to bones by tendons. Tendons are strong, fibrous cords of connective tissue that connect muscles to bones. They are made up of collagen fibers that are able to withstand the tensile forces created when muscles contract and pull on bones. When a muscle contracts, it pulls on the tendon, which in turn pulls on the bone, causing it to move. This is how muscles are able to control movement of the body. Without tendons, muscles would not be able to effectively transmit their forces to the bones, making movement difficult or impossible.