DOMS, short for Delayed Onset Muscle Soreness, is the muscle stiffness and tenderness that shows up 24 to 48 hours after unusually hard or unfamiliar exercise, like a long run or a race. It's a normal response to muscle stress, not an injury, and it usually eases within a few days.
Microscopic strain to muscle fibres, especially from downhill running, a long race, or a new type of workout, triggers an inflammatory response as muscles repair. This is what produces the soreness and stiffness a day or two later.
Typically 2 to 4 days, peaking around 24 to 48 hours after the run and fading gradually from there. If soreness lingers well beyond that or gets worse, it's worth getting checked rather than assuming it's still just DOMS.
Light movement, gentle stretching, hydration, and sleep all help. There's no instant fix, but easy activity like walking or a slow recovery run often feels better than staying completely still.
Light, easy running is usually fine and can even ease the stiffness. Sharp, one-sided, or joint pain is different from general muscle soreness, so see a doctor or physiotherapist if something feels off rather than just sore.
No, on its own it's a normal training response, not damage that needs treatment. Persistent pain, swelling, or pain that doesn't fit the usual DOMS pattern is worth having a professional look at.