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Every January gym memberships spike and the wait to get on the treadmill gets longer. This happens because about 40 percent of Americans make New Year’s resolutions, the most common of which are exercising more and improving fitness. Some people may believe in the concept of “no pain no gain,” but it’s a common misconception that if your muscles don’t feel sore then you are not working out hard enough. Many athletes reach for nonsteroidal anti-inflammatory drugs (NSAIDs) to ease the aches and pains of a hard workout. Naproxen and ibuprofen are two commonly used NSAIDs that are available over the counter. Studies estimate that up to 75 percent of long-distance runners take NSAIDs before, after or during training.

Microscopic tears in the muscles cause soreness following strenuous exercise. In response to injury, the body produces compounds called prostaglandins, which play an important role in healing. NSAIDs reduce pain by slowing the production of prostaglandins, which reduces inflammation. The problem is that inflammation also plays an important role in healing damaged muscle as well as helping the muscle growth that occurs with regular exercise. In other words, taking NSAIDs after a workout may not necessarily be a good thing.

A recent study in mice found that levels of a specific prostaglandin increased after minor muscle injury. This particular prostaglandin stimulated regeneration of new muscle stem cells to repair the damage. But when the mice were given NSAIDs their bodies produced fewer active stem cells, leading to weaker muscles even after the injuries had healed.

Other negative effects, such as kidney injury, have been associated with NSAIDs. In one study, elite athletes took either 400 milligrams of ibuprofen or a placebo every four hours during a 50-mile race. At the end of the race, more than 40 percent of the runners tested high for creatinine, a marker of kidney injury. Runners who took ibuprofen instead of the placebo were more likely to develop kidney injury and their degree of injury tended to be worse. The study did not explain why ibuprofen may cause kidney injury in elite athletes, and it’s not clear whether the risks are similar in people participating in less-intense workouts. More studies are needed to examine the effects of ibuprofen following different types of exercise.

If exercising is one of your New Year’s resolutions, start off slow to avoid muscle pain. If you do overdo it, try easing your aches with a warm heating pad before reaching for the ibuprofen.

John Chatham, DPhil, FAPS, is a professor of pathology and director of the Division of Molecular and Cellular Pathology at the University of Alabama at Birmingham.