Delayed onset muscle soreness (DOMS)
Evidence: moderate
The soreness that peaks one to three days after unfamiliar or hard running is caused by microscopic muscle and connective-tissue damage, not lactic acid. It is normal and self-limiting, a single bout protects you against the next one (the repeated-bout effect), and no recovery modality reliably removes it. Soreness is a poor guide to either training quality or injury.
Delayed onset muscle soreness is the dull ache and stiffness that sets in the day after unaccustomed or unusually hard exercise. It is at its worst when the work involved a lot of eccentric (lengthening) muscle action: downhill running, heavy strength work, plyometrics, or simply a harder or longer session than the body is used to.
It is not lactic acid
The popular explanation, that lactic acid builds up in the muscle and causes the soreness, is wrong. Lactate is cleared within an hour or two of stopping, long before soreness appears, and it is a fuel the body reuses, not a waste product. DOMS instead reflects microscopic damage to the muscle fibres and the connective tissue around them, followed by an inflammatory response and sensitisation of the local pain receptors (Cheung, Hume & Maxwell 2003). This is the same exercise-induced muscle damage that drives part of the muscular adaptation to training, which is why it is a normal feature of progressing, not a fault to be eliminated.
The time course
Soreness follows a consistent curve: it appears around 12 to 24 hours after the session, peaks between 24 and 72 hours, and resolves within five to seven days (Cheung, Hume & Maxwell 2003). Alongside the ache, the muscle is temporarily weaker and stiffer and the range of motion is reduced, all of which recover on a similar timeline. This is distinct from the sharp, localised, often sudden pain of a muscle strain: DOMS is diffuse, both-sided when the load was symmetrical, and comes on the next day rather than during the run.
The repeated-bout effect
The most useful thing to know about DOMS is that it protects against itself. A single bout of damaging exercise makes the muscle markedly more resistant to damage and soreness from the next similar bout, an adaptation called the repeated-bout effect that lasts weeks to months (Hyldahl, Chen & Nosaka 2017). In runners, a second bout of downhill running produced about half the strength loss of the first, with smaller soreness and a smaller rise in creatine kinase, a blood marker of muscle damage (Khassetarash et al. 2021). The protection comes from several adaptations together, chiefly neural changes, altered muscle mechanics and remodelling of the connective-tissue matrix, rather than from a quieter inflammatory response (Hyldahl, Chen & Nosaka 2017).
The practical lesson is to introduce new stressors gradually and then repeat them. The first downhill session, the first set of fast reps, or the first week back after a layoff will hurt; the same work a week or two later will not. This is why progressions in training load should be gradual, and why a single unaccustomed session is a poor reason to panic about fitness.
Soreness is a poor guide
DOMS tempts two mistakes. The first is reading soreness as a measure of a session’s quality, chasing the ache as proof of a good workout. Soreness tracks how unaccustomed the work was, not how productive it was: a well-judged threshold run that drives real adaptation may leave no soreness at all, while a novel movement that does little for running fitness can leave you wrecked. The second is reading it as the size of the damage, when in fact soreness correlates poorly with markers of actual muscle damage (Cheung, Hume & Maxwell 2003). Use it as a rough signal that the work was new, not as a training target.
What actually helps
Honestly, not much, and nothing that abolishes it. No treatment reliably removes DOMS; most give inconsistent or only short-term symptomatic relief (Cheung, Hume & Maxwell 2003). The recovery modalities commonly sold for it, massage, foam rolling and compression, ease the feeling of soreness modestly without speeding the underlying repair. Active recovery, light easy movement, eases stiffness while it is being done. Cold water immersion reduces soreness but at the cost of blunting some of the training adaptation, so it is the wrong tool after a session whose point was to adapt.
How to handle it
Keep moving rather than resting completely, drop the intensity for a day or two until strength and coordination return, and let the repeated-bout effect do the real work by reintroducing new stressors gradually. If pain is sharp, localised, one-sided, or present during the run rather than the day after, treat it as a possible injury, not as DOMS.