Why do muscles get sore after exercise?
Muscles often get sore a day or two after hard or new exercise because of tiny injuries to muscle fibers and the inflammation that follows. This is called delayed onset muscle soreness, or DOMS.
DOMS usually starts 12 to 24 hours after exercise and peaks around 24 to 72 hours. It is most common after exercises that involve lengthening a muscle under load, such as running downhill, lowering weights or doing squats. The body repairs the small tears, and the muscle becomes stronger and more resistant to damage.
For a long time, people blamed lactic acid for muscle soreness. Scientists now know that lactate is cleared from muscles within an hour or so after exercise, so it does not cause soreness days later. The burning feeling during intense exercise is a separate effect.
Easing soreness
Soreness usually goes away on its own within a few days. Gentle movement, light stretching, massage and rest can help. Increasing exercise gradually reduces soreness. Sharp pain, swelling or pain that lasts more than a week may signal an injury and should be checked by a doctor.
Did You Know?
The repeated bout effect means muscles adapt quickly. Doing the same exercise again a week later usually causes much less soreness.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.