Ask Well: Why Do Muscles Ache a Day or Two After Exercise?

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Welcome to the equivocal effects of delayed onset muscle soreness, the scientific term for aches that accumulate and intensify a day or two after a strenuous workout. Usually, D.O.M.S. involves not just pain but also “loss of strength and range of motion in the affected area,” said Scott Sailor, a professor of kinesiology at Fresno State University in Fresno, Calif., and the president of the National Athletic Trainers’ Association.

D.O.M.S. commonly occurs after exercise that involves lengthening muscles while they contract, Dr. Sailor said, such as running downhill. But it can develop after any exertion that is more intense or prolonged than is normal for you.

Such strenuous workouts can cause multiple slight tears to the muscle tissue, after which a variety of cells and substances migrate to these muscles to help them start healing.

Interestingly, these substances are not necessarily the same as those that arrive after a more severe muscle injury. Molecules that promote inflammation and swelling, for instance, tend to predominate in tissues affected by a serious injury, but can be absent in tissue affected by D.O.M.S., recent studies show.

Similarly, “there was a time when we attributed the muscle soreness to lactic acid,” Dr. Sailor said. “We have now learned that lactic acid leaves the muscle so quickly” that it cannot be involved in causing D.O.M.S.

In essence, researchers remain puzzled about what cellular reactions cause D.O.M.S.

Likewise, there is controversy about how best to treat it.

“Various treatments have been attempted over the years,” said Dr. Sailor, including massage, icing and anti-inflammatory painkillers. “At best, they have decreased the perception of pain,” he said, but only temporarily. No treatment yet has been shown to actually reduce the length of time that muscles remain sore and weak.

So if you do develop D.O.M.S., accept that, for the next five to seven days, you are going to be sore. Refrain from strenuous exercise during this time, Dr. Sailor said, although gentle walking is fine.

And, if it is any consolation, your muscles should be stronger after they recover.

In your future workouts, Dr. Sailor said, increasing the duration or intensity gradually should increase strength and fitness to limit the potential of experiencing the effects of D.O.M.S.