delayed-onset muscle soreness
/ DOMS /
You try a new workout, feel fine that evening, then wake up a day or two later with muscles that ache and feel stiff every time you move. The puzzle is the delay — the soreness peaks long after the exercise is over. This familiar experience is delayed-onset muscle soreness, or DOMS.
DOMS is the dull, tender ache that appears roughly 12 to 24 hours after unaccustomed or intense exercise, peaks around 24 to 72 hours, and fades within a few days. It follows exercise that involves muscles lengthening under load — the lowering phase of a movement, like walking downhill or easing down from a squat — which causes tiny disruptions in the muscle fibres and a low-grade inflammatory, repair response that sensitizes the area. It is a normal part of adaptation, not an injury, and after the muscle recovers it is more resistant to the same soreness next time (the 'repeated-bout effect').
In rehabilitation, recognising DOMS matters in two ways. First, it lets clinicians and patients tell ordinary post-exercise soreness apart from warning signs of real injury — DOMS is diffuse, symmetrical, eases with gentle movement, and resolves on schedule, whereas a sharp, localized, or worsening pain does not. Second, it argues for starting gently and progressing gradually: a deconditioned patient pushed too hard on day one may be too sore to participate for days, derailing the plan. Reassuring an anxious patient that this ache is expected and harmless can be the difference between them continuing and quitting.
Eager on his first day of rehab, a patient does far more leg work than usual. Two mornings later his thighs are so sore he can barely sit down — a textbook case of DOMS that a slower start would have avoided.
DOMS is normal adaptation, but overdoing day one can sideline a patient for days.
DOMS is not caused by lactic-acid build-up — a stubborn myth; lactate clears within an hour or two, while DOMS appears the next day and reflects muscle micro-damage and repair, not acidity.