Sore Muscles After a Workout: The Science of DOMS

The first workout of a new program often feels fine. It’s the next morning, or the morning after that, when you discover that stairs have become your enemy. This delayed soreness is so common that it has its own name: delayed onset muscle soreness, or DOMS.

What DOMS is

DOMS is the pain and stiffness you feel in your muscles from about one to five days after exercise you aren’t used to. It comes with a loss of strength, but that loss is temporary, and DOMS causes no permanent harm^[1]. It ranges from mild tenderness to pain that makes everyday movements hard, and it’s most common when you start a new kind of exercise or return to training after a break. It can also change how you move: soreness can reduce your range of motion and force, and leaning on other muscles to compensate may raise the risk of injury if you push hard too soon^[2].

Physiologists have studied it since at least 1902, when Theodore Hough, working at the Massachusetts Institute of Technology and the Boston Normal School of Gymnastics, published “Ergographic Studies in Muscular Soreness” in the American Journal of Physiology^[3]. More than a century later, the exact mechanism is still not settled^{[1, 2]}, but one popular explanation has been ruled out.

It isn’t lactic acid

The explanation you’ll hear most often is a buildup of lactic acid. It’s one of several theories researchers have proposed^[2], but the evidence points elsewhere. In a 1983 study, volunteers ran for 45 minutes on two occasions: once on level ground at a harder effort, and once down a 10% slope at an easier one. Only the downhill run caused significant soreness, in the glutes, the thighs, and the lower legs, along with a 351% rise the next day in creatine kinase, a blood marker of muscle damage. The harder level run caused no significant soreness at all^[4]. If lactic acid were to blame, the harder run should have hurt more.

The real trigger: lowering under load

What made the downhill run different was the type of muscle work. Running downhill, your thigh muscles spend much of each stride braking: contracting while they’re being stretched. This is called an eccentric contraction. Concentric contractions shorten a muscle to start a movement; eccentric ones lengthen it to slow a movement down^[5]. In the gym, lowering a weight under control is eccentric work, like lowering the bar in a Romanian deadlift while your hamstrings stretch.

In people who aren’t used to it, eccentric exercise damages muscle fibers and leaves them stiff and sore the next day. The leading explanation is that some of the tiny contractile units inside the fibers, called sarcomeres, get overstretched and disrupted^[5]. A widely cited model describes what follows: the damage disturbs the fibers’ calcium balance, the injured tissue breaks down over about two days, and substances released as the body clears the damage stimulate pain-sensing nerve endings in the muscle. That is what you feel as soreness^[1].

Why the second workout hurts less

The good news is that muscles adapt quickly. A single bout of eccentric exercise protects the same muscles against damage from the next one, a phenomenon called the repeated bout effect^[6]. Repeat the same exercise a week later and there’s much less damage^[5], and training regularly at the activity that made you sore reduces the soreness^[1]. Researchers think several changes play a part: in how the nervous system recruits the muscle, in the muscle’s stiffness, and in the fibers themselves, which may add sarcomeres so that each one is stretched less^[6].

Does soreness mean your workout worked?

It’s tempting to treat soreness as proof of a good workout. It isn’t. In a 2016 study, researchers followed volunteers through ten weeks of strength training, measuring muscle damage and muscle protein building in the first, third, and tenth weeks. In the first week, damage was at its highest, and so was protein building, but neither was related to how much muscle the volunteers eventually gained. Growth tracked protein building later in training, after the damage had faded^[7].

In other words, the soreness of your first weeks mostly reflects your muscles meeting a new challenge. As you keep training, the soreness fades while the gains continue.

What helps, and what doesn’t

A 2018 meta-analysis compared recovery methods and found that active recovery, massage, compression garments, water immersion, contrast water therapy, and cryotherapy all reduced DOMS, by small to large amounts. Massage worked best^[8]. Gentle exercise helps too, though only while you’re doing it: moving the sore muscles eases the pain, but it returns afterward^{[1, 2]}.

Stretching, on the other hand, barely helps. A Cochrane review of 12 studies found that stretching before exercise reduced next-day soreness by about half a point on a 100-point scale, and stretching afterward by about one point^[9]. If you’re very sore, the simplest approach is to go easier for a day or two: a review of DOMS advises athletes who train daily to reduce the intensity and duration of their exercise for one to two days after a session that causes intense soreness^[2].

When soreness is a warning sign

Ordinary DOMS is uncomfortable but harmless. Rarely, extreme exertion can cause rhabdomyolysis, a serious breakdown of muscle tissue; researchers describe exertional rhabdomyolysis as the extreme form of DOMS^[1]. Its symptoms include dark, red, or cola-colored urine, passing less urine than usual, and weakness, along with muscle pain, stiffness, and tenderness. Severe exertion, such as marathon running, is one known cause^[10]. If you notice these symptoms, contact a doctor. Pain that is sharp, sudden, or centered on a joint rather than spread through a muscle is also worth getting checked, since it may be an injury rather than DOMS.

Putting it into practice

• Start lighter than you think you need to. Begin a new program or exercise with fewer sets or lighter weights, and build up over the first few weeks as the repeated bout effect kicks in. Our guide to how many sets and reps to do has starting points.
• Don’t skip the lowering phase. It’s a big part of what makes lifting work: the 2026 American College of Sports Medicine review found that emphasizing it, known as eccentric overload, enhanced muscle growth^[11]. The 3D workout guides show a controlled lowering for every lift.
• Keep moving. Light activity and massage ease soreness better than rest or stretching^{[1, 8, 9]}.
• Don’t chase soreness. Track your weights and reps instead. Steady progress, not pain, is the sign your training works. Read more about progressive overload.