Delayed onset muscle soreness

Overview
Delayed Onset Muscle Soreness (DOMS) is the pain or discomfort often felt 24 to 72 hours after exercising and subsides generally within 2 to 3 days. Once thought to be caused by lactic acid buildup, a more recent theory is that it is caused by tiny tears in the muscle fibers caused by eccentric contraction, or unaccustomed training levels. Since lactic acid disperses fairly rapidly, it could not explain pain experienced days after exercise.

Although the precise cause is still unknown, the type of muscle contraction seems to be a key factor in the development of DOMS. Exercises that involve many eccentric contractions, such as downhill running, will result in the most severe DOMS. This has been shown to be the result of more muscle cell damage than is seen with typical concentric contractions, in which a muscle successfully shortens during contraction against a load.

Some research claims that DOMS is not caused by the pain from damaged muscle cells, but from the reinforcement process. The muscle responds to training by reinforcing itself up to and above its previous strength by adding new sarcomeres—the segments in the muscle fibrils. This reinforcement process causes the cells to swell and put pressure on nerves and arteries, causing DOMS.

Training with DOMS
DOMS typically causes stiffness, swelling, strength loss and pain. Continued exertion of sore muscles can cause further swelling and pain, and lengthen the period of muscular soreness. There is some scientific evidence that further training—a so-called second bout—has no negative effect on the reinforcement process. Training in a state of constant soreness would be uncomfortable, although one may be able to adapt to it. The relationship between muscular soreness, the rest required and hypertrophy is a contentious topic in bodybuilding. Claims that perpetual muscular soreness assures muscle growth are opposed by reports of stagnation through overtraining.

Stretching before and after exercising have been suggested as ways of reducing DOMS, as has warming up before exercise, cooling down after, and gently warming the area, though there is also evidence that the effect of stretching on muscle soreness is negligible.