Muscle Soreness

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Author: Richard Weil, MEd, CDE
Medical Editor: Jay W. Marks, MD

For some individuals, sore muscles are a reward after a hard workout. In fact, some people aren't happy unless they're sore after their workout, while others could live without it. Either way, all of us have probably experienced muscle soreness at one time or another. In this article, I'll review the causes, treatment, and prevention of muscle soreness.

What Causes Muscle Soreness?

One of the consequences of vigorous exercise—heavy weight lifting, a tough day of speed work on the track, or the stairclimber at the gym—is an accumulation of lactic acid in the muscles. Lactic acid is a normal byproduct of muscle metabolism, but it can irritate muscles and cause discomfort and soreness. Muscle soreness associated with exercise is known as delayed onset muscle soreness or DOMS. DOMS can make it difficult to walk, reduce your strength, or make your life uncomfortable for a couple of days.

But lactic acid isn't the only culprit in DOMS. In fact, lactic acid is removed from muscle anywhere from just a few hours to less than a day after a workout, and so it doesn't explain the soreness experienced days after a workout. What is it then that causes DOMS for days after exercise? The answer is swelling in the muscle compartment that results from an influx of white blood cells, prostaglandins (which are antiinflammatory), and other nutrients and fluids that flow to the muscles to repair the "damage" after a tough workout. The type of muscle damage I am referring to is microscopic (it occurs in small protein contractile units of the muscle called myofibrils) and is part of the normal process of growth in the body called anabolism. It is not the type of damage or injury that you see your doctor about. The swelling and inflammation can build up for days after a workout, and that's why muscle soreness may be worse two, three, or even four days after a workout (it can take up to five days for muscles to heal completely depending on the intensity of the workout).

In 1983, in one of the first studies of the causes of DOMS, subjects ran level or downhill on a treadmill (downhill running causes more muscle damage than level running due to eccentric muscle contractions), and then afterward, subjects' perception of soreness, lactic acid levels, and muscle swelling was measured. Results showed approximately equal levels of lactic acid in both groups, but greater swelling in the downhill runners, and only downhill runners reported soreness. Since only the downhill runners were sore and the only difference between the level- and downhill-runners was the swelling, the investigators concluded that it was the swelling that caused the delayed onset muscle soreness and not the lactic acid, a finding consistent with the idea that lactic acid clears the muscle soon after exercise and is not responsible for DOMS.

Is Soreness a Prerequisite for Growth?

I'm occasionally asked if soreness after a workout is necessary to get results. Although there's no evidence to support this idea and individuals certainly get stronger even if they don't get sore, some people just aren't satisfied with their workout unless they're sore, and there may be some rationale for this logic. Remember, there must be microscopic damage to muscle fibers before there can be growth, so if you're sore, it means there was damage and thus growth must not be far behind. But again, there's no evidence that soreness is necessary for growth, and until we understand more about the process, it's probably enough to say that soreness could be a potential marker or predictor of how much growth there will be. In the meantime, I've included three tips for increasing muscle growth, and increasing the likelihood of soreness for those of you who crave it.