Postexercise muscle soreness, also known as delayed-onset muscle soreness (DOMS), is defined as the sensation of discomfort or pain in the skeletal muscles following physical activity, usually eccentric, to which an individual is not accustomed.
The incidence of DOMS is difficult to calculate, because most people who experience it do not seek medical attention, instead accepting DOMS as a temporary discomfort. Every healthy adult most likely has developed DOMS on countless occasions, with the condition occurring regardless of the person’s general fitness level. However, although it is experienced widely, there are still controversies regarding the origin, etiology, and treatment of DOMS.
Eccentric muscle contractions
Exercise involving eccentric muscle contractions results in greater disruption or injury to the muscle tissues than does concentric exercise. Thus, any form of exercise with eccentric muscle contractions causes more DOMS than does exercise with concentric muscle contractions. Ample evidence from histologic studies, electron microscopic examination, and serum enzymes of muscular origin supports this notion.
To produce a given muscle force, fewer motor units are activated in an eccentric contraction than in a concentric contraction. In eccentric contractions, the force is distributed over a smaller cross-sectional area of muscle. The increased tension per unit of area could cause mechanical disruption of structural elements in the muscle fibers themselves or in the connective tissue that is in series with the contractile elements; however, it has not been proven that injury to muscle cells or to connective tissue is the causative factor in DOMS.
Muscle pain mechanism
The sensation of pain in skeletal muscle is transmitted by myelinated group III (A-delta fiber) and unmyelinated group IV (C-fiber) afferent fibers. Group III and IV sensory neurons terminate in free nerve endings. The free nerve endings are distributed primarily in the muscle connective tissue between fibers (especially in the regions of arterioles and capillaries) and at the musculotendinous junctions. The larger myelinated group III fibers are believed to transmit sharp, localized pain. The group IV fibers carry dull, diffuse pain.
The sensation of DOMS is carried primarily by group IV afferent fibers. The free nerve endings of group IV afferent fibers in muscles are polymodal and respond to a variety of stimuli, including chemical, mechanical, and thermal. Chemical substances that elicit action potentials in muscle group IV fibers in order of effectiveness are bradykinin, 5-hydroxytryptamine (serotonin), histamine, and potassium.
Only temporary morbidity (pain, soreness, reduced muscle performance) is associated with DOMS. Diminished performance results from reduced voluntary effort due to the sensation of soreness and from the muscle’s lowered inherent capacity to produce force.
No evidence exists to support the idea that DOMS is associated with long-term damage or reduced muscle function. Animal studies indicate that injured muscles regenerate during the period following exercise and that the process essentially is completed within 2 weeks.
Sex- and age-related demographics
Stupka and colleagues showed that muscle damage following unaccustomed eccentric exercise is similar in males and females; however, the inflammatory response is attenuated in women.
MacIntyre and coauthors found that the patterns of DOMS and torque differed between males and females after eccentric exercise.
In a study by Dannecker and colleagues, no sex differences were detected, except that higher affective ratios were reported by men than by women.
DOMS generally is not reported in children. Adults of all ages can experience DOMS.
With regard to lab studies, the serum creatine kinase (CK) level usually is elevated in DOMS, but it is nonspecific.
The diagnostic efficacy of imaging studies in DOMS has also been investigated. In a study by Dierking and colleagues, diagnostic ultrasonography, when used in the diagnosis of DOMS, was not sensitive enough to detect changes in a cross-sectional muscle area.
Magnetic resonance imaging (MRI) can detect muscle edema in DOMS but is not indicated clinically for the diagnosis. In a prospective evaluation of DOMS, abnormalities found in MRI persisted up to 3 weeks longer than did symptoms.
The patient needs to be educated concerning a specific progressive exercise training program before engaging in a heavy, unaccustomed exercise, particularly one that involves eccentric muscle contractions. For patient education information, see Muscle Strain.
Consultation with the patient’s athletic trainer and coach may be indicated.