Why Do Muscles Hurt After Training? Understanding DOMS
That sore, aching feeling in your muscles a day or two after a hard workout — especially after trying something new or intense — is one of the most universal experiences in exercise. It has a formal name: delayed onset muscle soreness (DOMS). Understanding what it is (and is not) helps you train smarter and avoid unnecessary worry.
What causes DOMS
DOMS is caused by microscopic damage to muscle fibers — particularly from eccentric contractions, where the muscle lengthens under load (the lowering phase of a bicep curl, downhill running, squats). This micro-damage triggers a local inflammatory response, fluid accumulation, and sensitivity of pain receptors. It typically peaks 24-72 hours after exercise and resolves within 3-7 days.
What helps
- Light movement: gentle walking or cycling increases blood flow and can temporarily reduce the ache.
- Massage or foam rolling: may provide short-term relief from soreness.
- Cold water immersion: can reduce soreness, though (as with other recovery tools) it should be timed sensibly relative to training goals.
- Sleep and nutrition: adequate protein and sleep give the body what it needs to repair the micro-damage.
- Gradual progression: the best "treatment" is prevention — progress volume and intensity gradually, especially when starting something new.
What DOMS is NOT
- Not a reliable marker of a good workout: you can have a highly effective session with little or no soreness, and vice versa. Soreness mostly reflects unfamiliarity and eccentric load, not muscle growth.
- Not a reason to stop training: training through mild DOMS is generally fine; the soreness itself is not damage that requires rest.
When to worry
Seek medical evaluation if pain is sharp rather than achy, is one-sided or localized to a specific spot, is accompanied by swelling, bruising, or weakness, or if you have dark urine after very intense exercise (a possible sign of rhabdomyolysis — rare but serious). These are signs of injury or overexertion beyond normal DOMS.
This article is for general educational purposes and is not a substitute for individualized medical advice.
Helpful products
- Foam roller — a simple tool for self-massage relief of muscle soreness.
Source: ACSM & exercise physiology literature
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