Kate Gosselin feels best when she runs 10 miles every other day, according to Us Weekly. But what the 37-year-old mother of eight doesn’t know is that when it comes to vigorous exercise, more isn’t always better. Turns out, people who work out too hard for too long may be less healthy than sedentary people, and are more likely to die than moderate exercisers, according to an editorial recently published in the British journal Heart.

The editorial authors reviewed decades’ worth of research on the effects of endurance athletics. They found numerous studies that showed that moderate exercise was good, but excessive exercise was damaging. For instance, in one German study published in European Heart Journal, researchers compared the hearts of 108 chronic marathoners and sedentary people in a control group. Surprisingly, the runners had more coronary plaque buildup, a risk factor for heart disease.

In another observational study, researchers tracked over 52,000 people for 30 years. Overall, runners had a 19 percent lower death risk than non-runners. However, the health benefits of exercise seemed to diminish among people who ran more than 20 miles a week, more than six days a week, or faster than eight miles an hour. The sweet spot appears to be five to 19 miles per week at a pace of six to seven miles per hour, spread throughout three or four sessions per week. Runners who followed these guidelines reaped the greatest health benefits: their risk of death dropped by 25 percent, according to results published in the journal Medicine & Science in Sports & Exercise.

Forget about chaffing and sore muscles: excessive exercise can cause even more serious wear and tear on your body. During a strenuous workout, your body works hard to burn sugar and fat for fuel. And just like burning wood in a fire, this creates smoke. The “smoke” that billows through your system is actually free radicals that can bind with cholesterol to create plaque build up in your arteries, and damage your cells in a process known as oxidative stress.

“Your body is designed to deal with oxidative stress that comes from exercise for the first hour,” says cardiologist James O’Keefe, MD, Director of Preventative Cardiology at the Saint Luke’s Mid America Heart Institute in Kansas City, and author of the Heart editorial. “But prolonged intense exercise causes excessive oxidative stress, which basically burns through the antioxidants in your system and predisposes you to problems.”

However, O’Keefe insists that this is no excuse to trash your running shoes and take to the couch. “Exercise may be the most important component of a healthy lifestyle, but like any powerful drug you’ve got to get the dose right,” he says. It’s true: exercise—in moderation—can reduce your risk of heart disease, high blood pressure, type 1 diabetes, Alzheimer’s, dementia, obesity, and premature aging. Regular workouts can also promote muscular health, skeletal health, and boost your mood. Overdo it, though, and many of these health benefits practically vanish.

Researchers are still working to define the safe limits for vigorous exercise. The bottom line: if you work out to promote your long-term health and well-being, doing vigorous exercise for longer than an hour isn’t necessary, and is actually counterproductive, says O’Keefe. Use these tips to maximize the benefits of moderate exercise:

If you like to work out every day: Don’t do hard endurance exercise for more than one hour per day, and listen to your body: if your muscles are sore, consider building in a day of “rest” and swap hard-core cardio for walking or stretching.

If you want to work out longer than 60 minutes a day: After the first 45 to 60 minutes of vigorous exercise, switch it up by doing yoga, strength training, or lighter activity like swimming—and don’t race.

If you’re already training hard: Researchers don’t know for sure whether cutting back on sustained endurance exercise (i.e., running more than 25 miles a week for the past ten years) can undo the damage done, and improve a person’s health. (O’Keefe’s guess is yes, though, based on related animal studies with promising results.) If you typically wake up with low energy, see no improvement in your fitness, have you lost your appetite, or have begun to think of workouts as a chore, you might have reached your personal threshold. Use common sense and cut back; like your muscles, your heart may need a day off from daily vigorous exercise. You don’t need to lay around, but stick to walking or yoga instead of your regular workout for one extra day each week.

If you want a work out that helps you live longer: Sprint for 20 to 40 seconds, then let your heartbeat return to normal, and repeat five to eight times. According to O’Keefe, high-intensity interval training can improve your fitness without taking a long-term toll on your health.

If “run a marathon” is on your bucket list, no matter what: “People do a lot of things for reasons besides living longer, like jumping out of airplanes and racing cars. We’re not saying those are bad, but they’re not for your health,” says O’Keefe. The same goes for marathon running. There’s no firm information that running a few marathons is going to hurt you. Just know that competing regularly (i.e., running one race per year for a decade) won’t promote longevity.

More from WH:
Quiz: Are You Setting Yourself Up For Running Injuries?
Running for Beginners
Best Workouts for a Total Body Transformation

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