Peter A. Huijbregts, PT, OCS, FAAOMPT
Abstract: This article reviews relevant muscular anatomy and describes the metabolic, temperature, and mechanical hypotheses as possible mechanisms of muscle injury. It describes the four stages of muscle injury, regeneration, and repair: Ca2+-overload, autolysis, phagocytosis, and regeneration/repair. The article concludes with some likely clinical implications for prevention and treatment of muscle injury.
Key Words: Muscle, Injury, Regeneration, Repair
A plethora of information is available in physical therapy literature on injury, regeneration, and repair of the connective tissues. This is understandable: after all, the different types of connective tissue (CT) make up a large part of the body. Knowledge of CT physiology and pathophysiology forms the basis for prevention and treatment of many injuries. In contrast, information on muscle injury, regeneration, and repair is not as readily available to physical therapists, yet muscle injury is common. It can be the result of mechanical forces; excessive tension may be generated during a passive stretch or a contraction, especially a lengthening or eccentric contraction1-4. Excessive mechanical force is also the reason for muscle injury due to contusions2, 4-10 and lacerations9, 10. Muscle injury can result from thermal stress, such as extreme heat or cold1, 6,7. Myotoxic agents can cause muscle injury. The local anesthetics marcaine6 and lidocaine in combination with epinephrine10 have been shown to cause muscle fiber necrosis. Excessive doses of corticosteroids10 and certain snake and bee venoms are also myotoxic1. Prolonged ischaemia also disrupts muscle; clinically this may be seen in compartment syndromes but also after the tourniquet application commonly used to create a bloodless field for surgical procedures4, 6,9-11.
The goal of this article is to increase the therapist’s understanding of muscle injury, regeneration, and repair. An increased understanding of the process of muscle injury and subsequent regeneration or repair can provide us with a theoretical basis for more appropriate prevention and treatment of muscle injuries. In this article relevant anatomy is reviewed. This will better allow for a discussion of possible causative mechanisms and the stages of muscle injury, regeneration, and repair. A review on the effectiveness of interventions to prevent or treat muscle injury is outside the scope of this article, but some possible clinical implications of the information will be discussed.