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LINDA WERTHEIMER, host:

This is MORNING EDITION from NPR News. I'm Linda Wertheimer.

RENEE MONTAGNE, host:

And I'm Renee Montagne. Good morning.

Today in "Your Health," a technique that might ease the pain in your back. First, let's hear about something that might not be causing the pain in your knees -jogging. It's a clich� among runners that eventually, jogging breaks down the knee joint. Researchers say that's not true. NPR's Patti Neighmond explains why.

(Soundbite of running footsteps)

PATTI NEIGHMOND: Paul Rider loves to run on Mulholland Drive in Hollywood.

Mr. PAUL RIDER: Fantastic view. Had a lot of rain, so you can see the whole San Fernando Valley. It's beautiful. It's a great place to run.

NEIGHMOND: Rider doesn't just run for exercise.

Mr. RIDER: It's a nice emotional release. Quite a nice stress release.

NEIGHMOND: Rider runs a seven- to eight-minute mile. His wife, Lyra, runs a little slower, but pretty much for the same reasons.

Ms. LYRA RIDER: I do enjoy running. I like getting out. It always feels great when you've done it.

NEIGHMOND: Lyra and Paul Rider are in their mid-40s, about the age when health experts used to say...

Dr. DAVID FELSON (Boston University School of Medicine): That if you jogged and jogged and ran and ran, that you'd be doing in your knees.

NEIGHMOND: Dr. David Felson, at Boston University School of Medicine, says the concern was degeneration of the knee, and arthritis. But when researchers actually studied the impact of running on knees, that's not what they found.

Dr. FELSON: When we look at people with knee arthritis, we don't find much of a previous history of running. And when we look at runners and follow them over time, we don't find that their risk of developing osteoarthritis is increased anymore than would be expected.

NEIGHMOND: So from both types of studies, the message is the same: Running won't hurt the knees even when you're older. And a new analysis of 28 studies from around the world, which included nearly 10,000 people, concluded the same thing.

In one study, researchers from Sweden found it may be even beneficial. They looked at exercise, including running, to see what happened to cartilage - that gooey substance which connects bones and muscle. Dr. Felson.

Dr. FELSON: They took people at risk of osteoarthritis - and took one group and exercised it; and the other group, and didn't. And they did imaging of the joint that looks at the biochemistry of cartilage, where the disease may start.

And they found that the biochemistry, which was abnormal at the beginning, actually improved a little bit in those who were running, suggesting that running was healthy to the joint.

NEIGHMOND: It could be the impact of the body weight, when the foot hits the ground, stimulates production of certain proteins in the cartilage, which make it stronger in the same way exercise like running makes bones and muscles stronger. And cartilage health may turn out to be really important.

Dr. NANCY LANE (University of California Davis Center for Healthy Aging): We are now starting to understand that there is some loss of cartilage annually.

NEIGHMOND: Dr. Nancy Lane is a rheumatologist at the University of California. She did some of the first studies of runners and knee arthritis.

Dr. LANE: If you have a relatively normal knee, and you're jogging five to six times a week at a moderate pace, then there's every reason to believe that your joints will remain healthy.

NEIGHMOND: But there are some caveats. If you've had a significant knee injury -especially one that required surgery - then, Lane says, running can increase your risk of arthritis. So can running really fast - like a five- or six-minute mile, for example - or lots of really long runs, like marathons. Best advice, says Lane - running in moderation, about 40 minutes a day, an eight- to 10-minute mile.

And if you're more than 20 pounds overweight, Lane says don't start suddenly running. All that extra weight can cause real damage - inflammation, bony spurs, and cartilage thinning.

Dr. LANE: If somebody is heavy and they want to start exercising, I don't have them go off running. I have them walk and walk until they're to a point where I think that their body mass is reduced enough that it won't traumatize their joints.

NEIGHMOND: So for Paul and Lyra Rider, who aren't overweight and hope to run the rest of their lives, scientists agree: Just go for it.

Patti Neighmond, NPR News.

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