The soreness is felt most strongly 24 to 72 hours after the exercise. After such exercise, the muscle adapts rapidly to prevent muscle damage, and thereby soreness, if the exercise is repeated. The soreness is perceived as a dull, aching pain in the affected muscle, often combined with tenderness and stiffness. The pain is typically felt only when the muscle is sore throat muscle and joint pain, contracted or put under pressure, not when it is at rest.
Although there is variance among exercises and individuals, the soreness usually increases in intensity in the first 24 hours after exercise. It peaks from 24 to 72 hours, then subsides and disappears up to seven days after exercise. The soreness has been attributed to the increased tension force and muscle lengthening from eccentric exercise. This increases the risk of broadening, smearing, and damage to the sarcomere. This build-up of lactic acid was thought to be a toxic metabolic waste product that caused the perception of pain at a delayed stage.
This theory has been largely rejected, as concentric contractions which also produce lactic acid have been unable to cause DOMS. Additionally, lactic acid is known from multiple studies to return to normal levels within one hour of exercise, and therefore cannot cause the pain that occurs much later. Although delayed onset muscle soreness is a symptom associated with muscle damage, its magnitude does not necessarily reflect the magnitude of muscle damage. Soreness is one of the temporary changes caused in muscles by unaccustomed eccentric exercise. Other such changes include decreased muscle strength, reduced range of motion, and muscle swelling. It has been shown, however, that these changes develop independently in time from one another and that the soreness is therefore not the cause of the reduction in muscle function. Soreness might conceivably serve as a warning to reduce muscle activity so as to prevent further injury.
However, further activity temporarily alleviates the soreness, even though it causes more pain initially. Continued use of the sore muscle also has no adverse effect on recovery from soreness and does not exacerbate muscle damage. It is therefore unlikely that soreness is in fact a warning sign not to use the affected muscle. After performing an unaccustomed eccentric exercise and exhibiting severe soreness, the muscle rapidly adapts to reduce further damage from the same exercise. This is called the «repeated-bout effect».
As a result of this effect, not only is the soreness reduced, but other indicators of muscle damage, such as swelling, reduced strength and reduced range of motion, are also more quickly recovered from. The effect is mostly, but not wholly, specific to the exercised muscle: experiments have shown that some of the protective effect is also conferred on other muscles. The magnitude of the effect is subject to many variations, depending for instance on the time between bouts, the number and length of eccentric contractions and the exercise mode. It also varies between people and between indicators of muscle damage.