Most fitness advice urges people to squeeze in more workouts. That’s reasonable, considering government data show that only about a quarter of American adults meet the current guidelines for adequate physical activity: 150 minutes of moderate or 75 minutes of vigorous aerobic activity per week, plus two bouts of muscle-strengthening exercise.

Meeting these guidelines is important, since getting enough exercise can improve an individual’s physical and mental health. But when it comes to exercise, it is possible to have too much of a good thing. In fact, research suggests taking strategic time off from your workout routine can maximize the benefits of physical activity, and minimize the risks.

“Rest and recovery absolutely are necessary,” says Hunter Paris, an associate professor of sports medicine at Pepperdine University in California. “Fatigue, to a degree, is beneficial [because it signifies progress]. But there comes a point where fatigue can accumulate and overwhelm a bit.”

Studies back that up. One published in 2018 argues that there’s a “Goldilocks Zone” for exercise—that is, a sweet spot between getting too little physical activity (which is linked to a higher risk of heart disease and cancer, among other chronic illnesses) and too much (which, especially for middle-aged and older adults, can increase the risk for heart issues and premature death by placing too much strain on the body). The paper advises against doing more than four or five hours of vigorous exercise per week, and recommends at least one rest day.

Other research from 2017 suggests taking days off can protect against bone loss—which is of particular concern for women—and excess inflammation, a risk factor for many chronic diseases. Working out too much could even make you sick, one 2016 study suggests. In the small study, athletes who did intense workouts on back-to-back days saw a drop in proteins that help the immune system fight disease. Over-training also robs your muscles of the time they need to recover.

Paris hesitates to offer a one-size-fits-all prescription for rest. An Olympic-level athlete will have different recovery needs than someone who walks for exercise; similarly, some people might feel best when they take a full day off, while others may prefer active recovery (like stretching or lower-intensity exercise) to keep their momentum going. Rather than rigid rules, he says he recommends people take stock of how they’re feeling physically—things like fatigue, soreness and drops in performance—and mentally, and use that information to honestly decide whether more exercise will help or hurt.

It’s also important, Paris says, to recover with intention. “It’s possible for one to rest and recover while exercising,” he says, “and certainly it’s possible for one to not be exercising and also not be resting and recovering.” Skipping a workout to wake up extra-early and run errands, for example, might not help an athlete regain energy, while trading a high-impact workout for yoga might help gym-goers return to their normal routine feeling loose and refreshed.

Serial exercisers who feel guilty or restless on days off may benefit from reframing how they define physical activity, Paris says. Numerous studies show that activities not traditionally thought of as “exercise”—such as walking, cleaning, gardening and taking the stairs—can help prolong a person’s lifespan and reduce their risk of chronic disease. “If you’ve only got 30 seconds or one minute to get up and walk to the water cooler, that counts, he says. “That matters.”

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Write to Jamie Ducharme at jamie.ducharme@time.com.