A muscle strain, also known as a pulled muscle, is an injury to a muscle or a tendon, which is the fibrous tissue that connects muscles to bones. Minor injuries may only overstretch a muscle or tendon, while more severe injuries may involve partial or complete tears in these tissues. Strains commonly occur in the lower back and in the muscles at the back of the thigh (hamstrings). The difference between a strain and a sprain is that a strain involves an injury to a muscle or to the band of tissue that attaches a muscle to a bone, while a sprain injures the bands of tissue that connect two bones together.

Muscle strains can be caused by one event, such as using poor body mechanics to lift something heavy, or by repetitive injuries when you stress a muscle by doing the same motion over and over. Gripping sports, such as gymnastics or golf, can increase your risk of muscle strains in your hands, while elbow strains are often caused by throwing sports and racquet sports.

The key symptoms of a muscle strain are sudden pain that worsens while contracting the muscle, swelling and bruising, loss of strength, and range of motion. In mild cases, only a few muscle fibers are stretched or torn, and the muscle remains intact and strong. In severe cases, however, the strained muscle may be torn and unable to function properly. There are three grades of muscle strain to indicate how severe they are:

• Grade I strain: This strain stretches the muscle or tendon but doesnt tear it. Symptoms include pain, tenderness, and mild swelling, but you can still move the muscle.
• Grade II strain: This strain partially tears the muscle or tendon. Symptoms include pain, swelling, and weakness in the muscle, and you may have difficulty moving the affected area.
• Grade III strain: This strain tears the muscle all the way through, causing complete loss of muscle function, as well as considerable pain, swelling, tenderness, and discoloration. Because Grade III strains usually cause a sharp break in the normal outline of the muscle, there may be an obvious "dent" or "gap" under the skin where the ripped pieces of muscle have come apart.

Initial treatment for a muscle strain includes rest, ice, compression, and elevation. People often report the sensation of pain as the feeling of being "stabbed." When muscle is initially injured, significant in...