What Causes Sore Muscles After Exercise?

Last week (and much of the week before) I’ve been unable to keep up on my posts, due to an ongoing home construction project. I won’t chatter on about the details, but suffice it to say, the project involved a lot of shoveling dirt and digging trenches. So, now that I’m finally able to return to my blog, I’ll talk about something I’ve experienced since the last time I posted – muscle soreness!

Most of you have probably felt it at some point, whether you’re a casual gardener or a professional athlete – you feel great, if a little tired, right after a new workout, but a day or two later, your muscles grow stiff and sore, only to return to normal again within the week. So what’s going on here? Why do you feel fine right after working out, but sore hours later?

This phenomenon is called “delayed-onset muscle soreness” (abbreviated as DOMS), and there are actually a number of proposed explanations. It occurs most frequently after strenuous, unfamiliar exercise, especially if muscles have been undergoing “eccentric” movement, in which muscle fibers are being stretched despite trying to contract at the same time.

One popular – and probably untrue – explanation for DOMS that you might have heard bandied about is lactic acid buildup. While it’s true that lactic acid builds up in muscles during strenuous exercise (it’s a byproduct of anaerobic respiration, which happens when muscles aren’t getting enough oxygen), the body clears that away relatively quickly; therefore, lactic acid buildup doesn’t explain soreness that persists days after exercise. In addition, lactic acid buildup also occurs in non-“eccentric”-type muscle movements, which don’t usually result in DOMS.

The most likely explanation for DOMS is actually a combination of several proposed explanations: muscle damage, movement of enzymes out of muscle cells, and inflammation. According to this hypothesis, muscle tissue is damaged by new or unfamiliar “eccentric” movements, which tear some membranes within and around the cells, allowing enzymes and other molecules such as calcium to leak into the surrounding area. This stimulates an inflammatory response from the body, which leads to the pain, stiffness, and weakness you might feel a few days after an unfamiliar workout.

DOMS doesn’t pose much of a problem in and of itself, since the soreness will go away and damage will heal on its own within a few days, but you should be careful about exercising sore muscles. DOMS can cause temporary muscle weakness, so your usual level of activity becomes proportionately more intense, putting you at greater risk for a more serious muscle strain. That’s not to say that muscle soreness should stop you from exercising – it’s just wisest to be careful.

Several review articles have looked over possible ways to treat or prevent DOMS, but they found no clear standout treatment strategy. There have been a lot of studies looking into various treatments, but on the whole, these studies have been plagued by small sample sizes, shoddy research methods, and conflicting results. Applying ice and compression might help somewhat; the jury is still out on whether NSAIDs (non-steroidal anti-inflammatory drugs) are useful; massage, stretching, and nutritional supplements probably won’t do anything. Interestingly, the most effective treatment by far is light exercise, which will lessen the soreness and stiffness (though only for a little while). Furthermore, repetition of the same “eccentric” muscle movements will decrease DOMS over time, meaning that you might feel less sore after doing the same muscle movements in future workouts.

So if you feel stiff and sore from, say, spending a week shoveling dirt, then you might feel better if you went outside and shoveled a little more.

Cheung, Karoline, Patria A. Hume, Linda Maxwell. “Delayed Onset Muscle Soreness.” Sports Medicine Volume 33, Issue 2, pp. 145-164 (2003).
Connolly, Declan A.J., Stephen P. Sayers, Malachy P. McHugh. “Treatment and Prevention of Delayed Onset Muscle Soreness.” Journal of Strength and Conditioning Research Volume 17, Issue 1, pp. 197-208 (2003).


One thought on “What Causes Sore Muscles After Exercise?

  1. Pingback: Sore Muscles??? | Fit and Fab Life!

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