Why Your Muscles Ache a Day or Two After Exercise

You try a new exercise class, go for your first long walk in months, or spend a day moving furniture. You feel fine that evening. Then the next morning, getting out of bed is a struggle, and walking down the stairs is worse.

This delayed ache is so common it has a name: delayed onset muscle soreness, or DOMS.

What DOMS feels like

DOMS usually:

• Starts 12 to 24 hours after exercise.
• Peaks between 24 and 72 hours later.
• Fades within about five to seven days without any treatment.

The muscles feel tender, stiff and weaker than usual, and they hurt most when you stretch or use them. It is different from the sharp, sudden pain of an injury such as a pulled muscle, which you usually notice at the time.

What causes it

DOMS happens when muscles are asked to do something they aren’t used to, either a new kind of movement or more effort than usual.

It is especially linked to eccentric movements, where a muscle lengthens while it is working. Examples include lowering a weight slowly, walking or running downhill, and the downward part of a squat. These movements put a lot of strain on individual muscle fibres.

The strain causes tiny areas of damage in the fibres and the tissue around them. Over the next day or two, the body responds with inflammation as it clears up and repairs the damage. This process makes nerve endings in the muscle more sensitive, which is why the soreness builds up gradually rather than straight away.

The ache is a sign of repair, not of a fitter workout.

It isn’t lactic acid

Many people still believe that soreness is caused by lactic acid building up in the muscles. It isn’t.

During hard exercise, muscles produce lactate. It can contribute to the burning feeling you get during intense effort. But lactate levels return to normal within about an hour of stopping, long before DOMS begins. Studies also show that exercises that produce a lot of lactate, such as cycling uphill, cause less soreness than downhill running, which produces less.

The repeated bout effect

The good news is that DOMS gets much milder with practice. After one session of an unfamiliar exercise, muscles adapt quickly. Doing the same exercise again a week or two later usually causes far less soreness, even at the same effort. Scientists call this the repeated bout effect.

That’s why soreness is worst when you start something new or return after a long break, and why building up gradually is the best way to avoid it.

What helps

There is no instant cure, but some things make DOMS easier to live with:

• Gentle movement. Light walking, cycling or swimming eases stiffness for a while. Complete rest isn’t necessary.
• Massage. A 2018 review of 99 studies found that massage was one of the most effective ways to reduce soreness and feelings of fatigue after exercise.
• Time. DOMS goes away on its own.
• Painkillers, if needed. Follow the instructions on the pack, and ask a pharmacist if you aren’t sure which suits you.

Some things are less useful than people think:

• Stretching. A Cochrane review of 12 studies found that stretching before or after exercise made very little difference to soreness, a reduction of about one or two points on a 100-point scale.
• Ice baths. Some studies show a small reduction in soreness, but others suggest that regular cold baths after strength training may slightly reduce muscle gains over time.

Should you exercise when sore?

Light exercise is fine and can help. It’s usually better to avoid hard training of the very sore muscles until the worst has passed, because they are weaker and you may be more likely to strain them. You can work other muscle groups instead.

When to get medical help

Normal DOMS is uncomfortable but harmless. Rarely, very intense or unusual exercise can cause serious muscle breakdown called rhabdomyolysis, where damaged muscle releases substances that can harm the kidneys.

Get urgent medical help if, after exercise, you have:

• Severe muscle pain that is much worse than normal soreness, or doesn’t improve after a few days.
• Swelling in the muscles.
• Dark urine, like tea or cola, or passing much less urine than usual.

Also see a doctor if pain is sharp and started suddenly during exercise, or affects a joint rather than a muscle.