Muscle fibers are composed of microscopic proteins and other molecules that allow a muscle to contract. These fibers are what are injured and then repaired in a muscle strain. In addition, another kind of tissue is present in muscle which does not contract but helps support the overall structure of the muscle. This is connective tissue and, as the most abundant of the primary tissues of the human body, is present in many forms and has a wide variety of functions. As we will see later, damaged connective tissue has been implicated as one of the causes of delayed onset muscle soreness.
Muscle fibers make up the bulk of a muscle.
In order to attach to bones, they often blend into a different type of tissue which makes up tendons. Tendons generally cross a joint and help facilitate movement. For example, the quadriceps muscle on the front of the thigh has a large tendon that attaches to the shin bone. When this muscle contracts, the knee is straightened. A tendon is different from a ligament, which generally attaches from one bone to another bone and mainly serves to stabilize a joint.