Why Do Your Muscles Start To Ache Days After Working Out?

Exercise can be amazing for you: regularly getting active can reduce your risk of a whole host of ailments, such as heart attacks and strokes, and simply getting out for a walk can reduce your risk of death (although the infamous 10,000 steps goal is pretty arbitrary). Indeed, the World Health Organization states that those who don’t work out enough have a 20-30 percent increased chance of death. But if exercise is so good for you, why can it hurt so much – and why can the pain commence days after you’ve staggered out of the gym?

Picture the scene: You’re bashing out the squats, bench press reps, or whatever your exercise of choice is, and you’re really feeling the burn in your muscles. You finish your set, and the pain dissipates relatively quickly. Pleased with yourself, you head home – only for those very same muscles to start aching a couple of days later. What’s up with that?

The acute pain experienced during exercise is thought to be due to the byproducts of the cell’s production of energy building up and altering the environment within the muscle, activating pain receptors. Of course, pain that you suspect is caused by an injury is a sign to stop immediately.

That other, more delayed kind of pain has a name: Delayed Onset Muscle Soreness (DOMS). “Symptoms are often pain and tenderness in the affected muscles that are worse during movement,” Dr Tom Clifford, senior lecturer in physiology and nutrition at Loughborough University, told IFLScience.

Physician Theodore Hough is often cited as the first to describe DOMS. In a paper published in March 1902, Hough noted two different kinds of muscular soreness: “The first is very marked during work and may be noticeable for three or four hours afterward; it then passes away entirely,” he wrote. “The second kind, on the contrary, is not noticed at all at the time of [exercise] nor for sometime afterwards; it usually begins about eight hours after the work, increases to a maximum which may occur from ten to twenty-four, or even more hours later; indeed this soreness may not make its appearance until the second day after.”

Hough attributed the first kind to “the same causes as those which produce fatigue, namely the presence of the diffusible waste products of activity,” but on the other hand wrote that “there are reasons for thinking that the second kind of soreness is fundamentally the result of ruptures within the muscle.”

How far has our knowledge of DOMS come since Hough’s day?

Although it was once thought that DOMS could be caused by lactic acid buildup in the muscles, this is no longer thought to be the case. It’s often said that painful DOMS symptoms following strenuous, unfamiliar exercise are caused by micro-tears in muscle fibers. However, there is “still no general consensus on what the chief mechanism of DOMS is,” Clifford explained. Symptoms peak around 24-72 hours after exercise, “but typically you don’t know about it all immediately after or for a few hours after exercise. Hence, it seems to be caused by a delayed biochemical response.”

DOMS is “likely caused by a combination of skeletal muscle damage (structural damage to the proteins), disruptions to calcium homeostasis and inflammation, which ultimately sensitizes nociceptors,” which are sensory neurons that respond to potentially harmful stimuli, leading to pain, Clifford explained. “Key stimuli thought to cause the soreness are nerve growth factor, bradykinin, prostaglandin E2, and histamine.”

Bradykinin is a peptide hormone that plays a role in inflammation and pain control, and nerve growth factor (NGF) is a protein that has a role in the healing of injured tissue and how neurons transmit pain signals. One 2010 study in rats examining the role of the two in DOMS concluded that “bradykinin triggers development of muscular mechanical hyperalgesia and NGF serves in its maintenance by sensitizing muscle C-fiber receptors to mechanical stimulation.”

Prostaglandin E2 (PGE2) is a lipid that has hormone-like effects. A 2020 study indicated that bradykinin induces PGE2 release, and this could “provide a possible explanation for the role of bradykinin in inflammatory diseases, such as DOMS.” Histamine regulates the inflammatory response, and has also been associated with the uncomfortable symptoms of DOMS.

Clifford added that it’s “also suggested that DOMS stems more from the fascia surrounding the muscle than the muscle belly itself but [there’s] not lots of evidence to support either.”

The fascia is connective tissue that holds all your internal bits in place, and also has nerve endings. The authors of a 2021 review paper wrote that evidence suggesting a major role of this connective tissue in the development of DOMS is accumulating, and that “strain forces associated with eccentric contraction may cause micro-ruptures and inflammation of the deep fascia.”

Eccentric contractions, where the muscle is lengthened as it is contracted, are often pointed towards as the main cause of DOMS. One example of an eccentric contraction is the lowering part of a bicep curl. However, Clifford noted: “More recent research suggests that unaccustomedness to the exercise is more of a factor than eccentric contractions. You can get DOMS after concentric contractions too,” where the muscle shortens as it contracts. “It is possible that eccentric contractions are less familiar in everyday actions, hence they often result in more DOMS.”

Can DOMS be prevented or managed?

Can nutrition help manage the symptoms of DOMS? “Possibly – some studies show that phytochemical supplements derived from fruits and vegetables such as cherries and curcumin may help attenuate pain symptoms. But the effects are quite small and the studies not without limitations,” explained Clifford. “Essential fatty acids, like omega-3 fatty acids, may also attenuate symptoms of DOMS. There is a better mechanistic underpinning for why they may have analgesic effects, linked to the resolvins that help resolve inflammation.”

One 2018 review article looked at 99 studies on recovery techniques for DOMS, indicating that massage was the most effective method for reducing the symptoms. The authors also pointed towards water immersion and compression garments, but found that these had less of an effect.

Plenty of people stretch before and/or after exercise in the hopes that limbering up will help prevent soreness post-workout. However, while stretching has benefits, a 2011 Cochrane review suggests that preventing DOMS is not one of them. The review looked at 12 studies and found “very consistent findings” throughout: “There was little or no effect of stretching on the muscle soreness experienced in the week after the physical activity.”

If you’ve over-exerted yourself and feel the need to push through DOMS and get another session in, could this come with risks? It’s “possible that exercising when DOMS are severe that gait patterns change,” Clifford explained, “and this increased injury risk or that low-grade inflammation stemming from DOMS increases the risk of overtraining syndrome. But this is an understudied area, and these are more speculations.”

If you notice that your muscles tend to ache more after trying out a new workout, there’s a reason: for DOMS, the “main cause is [being] unaccustomed to the exercise,” Clifford said. “The more accustomed to the exercise [the] person is, or the more well-trained they are, the less DOMS they typically experience. Essentially, being fitter but especially stronger likely means you experience less DOMS.”

So if you want to avoid DOMS, don’t be afraid to exercise, but it’s a good idea to know your limits.

The content of this article is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of qualified health providers with questions you may have regarding medical conditions.

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.  

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