Or you're playing catch with the grandchildren when you suddenly feel a pull in your shoulder. These injuries are examples of muscle strains, often called muscle pulls.
Strains are tears or stretches in the muscle fibers or the tendons that connect muscles to bones.
Strains can range from relatively mild injuries, with some muscle fibers being torn, to large muscle tears with swelling and bleeding present. Muscle fatigue, which places additional stress on the muscle and connective tissue. The more active you are, the greater your risk of injury. Poorly conditioned people also are at risk when they do strenuous activity without proper pre-conditioning. It's therefore important to take the time to adequately prepare for your activity.