A Muscle strain is an excessive stretch or tearing of muscle fibers and related tissues. It can occur at one of the attachment sites or at any point along the length of the muscle. They are classified as either 1st, 2nd, or 3rd degree depending on the severity.
Excessive stretching or minor tearing of a few muscle fibers. The pain can often be localized with one finger. Some stiffness and weakness will also be present. If exercise is attempted, the pain and stiffness may decrease during the activity, but return after, often with much greater intensity.
Moderate tearing of muscle fibers with pain generally covering a larger area than the 1st degree strain. Stiffness and weakness will be felt and the painful area may appear black and blue due to bleeding within the injured muscle.
A complete tear of the muscle. Wide-spread bruising will be present and a "balling up" of the muscle may be seen or felt with your hand.