Delayed muscle soreness. The inflammatory response to muscle injury and its clinical implications
Delayed onset muscle soreness (DOMS) is a sensation of discomfort that occurs 1 to 2 days after exercise. The soreness has been reported to be most evident at the muscle/tendon junction initially, and then spreading throughout the muscle. The muscle activity which causes the most soreness and injury to the muscle is eccentric activity. The injury to the muscle has been well described but the mechanism underlying the injury is not fully understood. Some recent studies have focused on the role of the cytoskeleton and its contribution to the sarcomere injury. Although little has been confirmed regarding the mechanisms involved in the production of delayed muscle soreness, it has been suggested that the soreness may occur as a result of mechanical factors or it may be biochemical in nature. To date, there appears to be no relationship between the development of soreness and the loss of muscle strength, in that the timing of the two events is different. Loss of muscle force has been observed immediately after the exercise. However, by collecting data at more frequent intervals a second loss of force has been reported in mice 1 to 3 days post-exercise. Future studies with humans may find this second loss of force to be related to DOMS. The role of inflammation during exercise-induced muscle injury has not been clearly defined. It is possible that the inflammatory response may be responsible for initiating, amplifying, and/or resolving skeletal muscle injury. Evidence from the literature of the involvement of cytokines, complement, neutrophils, monocytes and macrophages in the acute phase response are presented in this review. Clinically, DOMS is a common but self-limiting condition that usually requires no treatment. Most exercise enthusiasts are familiar with its symptoms. However, where a muscle has been immobilised or debilitated, it is not known how that muscle will respond to exercise, especially eccentric activity.