Should You Exercise Less?

Maybe you’re a running junkie who can’t resist the lure of another marathon. Or maybe you just live in a city where climbing stairs—from the subway, to the office, to your walk-up apartment—is essentially unavoidable. Don’t get us wrong: All that activity is terrific for your health. It just might not be so great for your knees, finds new research.

Over a four-year period, researchers at the University of California, San Francisco tracked the activity levels of 200 healthy men and women between the ages of 45 and 60, none of whom had any history of knee pain. At the end of the study period, experts used MRI scans to measure the swelling in participants' knees. The results were clear: Compared to their moderately active counterparts, adults with the highest levels of physical activity were more likely to have knee-joint swelling, a classic sign of cartilage degeneration. 

Similar to oil that lubricates the cogs of a machine, cartilage is an elastic substance that covers your joints and allows them to move smoothly. It’s also been identified as one of the primary tissues responsible for the prevention of osteoarthritis, a painful joint disorder. Some degree of age-related cartilage degeneration is normal—but lose too much, and regular activities like bending, climbing stairs, and even walking can become more difficult. What’s more, “once cartilage is gone, there’s nothing you can do to repair or regrow it,” says study author Thomas Link, MD, PhD, Chief of the Musculoskeletal Imaging Section in the Department of Radiology and Biomedical Imaging at UCSF.

More from Prevention: Considering A Joint Replacement?

But don’t swear off workouts just yet: Study participants with the lowest levels of physical activity also experienced cartilage degeneration, because movement is necessary to circulate joint fluid that keeps cartilage healthy. So what types of exercise score top marks for knee health? And how often should you do them? Here’s how it breaks down:

Proceed with caution Three or more hours a week of high-impact activities like running, skiing, basketball, or soccer will likely hasten cartilage degeneration. Everyday activities that require you to bend your knees can do damage, too: Climbing more than 10 flights of stairs per day, kneeling or squatting for more than 30 minutes per day, or regularly lifting objects that weigh more than 25 pounds all increase stress on your knees, upping your chance of cartilage damage, Dr. Link says. 

Move (more) gently The activities that many of us find most the most relaxing are also the easiest on our knees. Walking, swimming, or bicycling will boost your heart rate while minimizing the impact on your joints. “An hour a day is fine,” Dr. Link advises. (To supercharge that stroll, find out how you can Burn More Calories Walking.)