Sport physicians and other medical personnel are frequently called on to evaluate soft-tissue injuries, particularly those involving the muscle-tendon unit. This should not be surprising, given that skeletal muscle constitutes the largest tissue mass in the body, comprising up to 45% of the total body weight. Skeletal muscle consists of individual muscle fibers, organized networks of nerves and blood vessels, and an extracellular connective tissue matrix. Each of these structures can be damaged, and the clinician must always keep this in mind when evaluating an injury.