A strain is the tearing of muscle fibers. Muscle fibers are the individual units that make up your muscles.
When you call upon the muscle to perform strong or repeated contractions, you may suffer a strain. To further confuse the layperson, strains are classified into grades I, II, and III. Another way to think of these grades is mild (grade I), moderate (grade II), severe (grade III).
A grade I strain is a mild disruption of the muscle fibers. There may be mild swelling, mild tenderness, and it may be painful to stretch and use the injured muscle.
A grade II muscle strain indicates moderate muscle fiber damage. The pain is moderate to severe, it definitely hurts to use and stretch the injured muscle, and ecchymosis may be present. Ecchymosis (commonly called bruising) indicates that there was internal damage to blood vessels that resulted in bleeding within and around the muscle. This bleeding is often visible under the skin as a purple, blue, red, yellow, and even green in color.
A grade III strain is the most severe. It is the complete tearing of a muscle into two pieces, or separation of the muscle from its associated tendon. There is severe pain, complete loss of muscle strength, swelling is normally present with ecchymosis, and there may be a palpable “indentation” where the muscle is torn. Medical intervention is usually necessary. Typically, an orthopaedist (musculoskeletal specialist) will evaluate your condition and surgical repair may be necessary.