TERRY GROSS, HOST:

Whether you're jogging or just walking around the office in high heels, you've got to watch out for your feet and your legs. We're going to hear Part Two of our interview with Gretchen Reynolds, who writes the "Phys Ed" column for the New York Times blog Well. She also has a new book about the latest research about exercise. It's called "The First 20 Minutes." Reynolds is an avid runner and in Part One of our interview, she explained that although running, when done right, can be good for you, most runners will eventually have to deal with a running-related injury.

What injuries have you had as a runner?

GRETCHEN REYNOLDS: Well recently, I hurt my iliotibial band, which runs along the outside of the knee. And I also hurt my Achilles tendon, which I had never done before. And I did that, I must admit, when I tried barefoot running.

GROSS: Mm. Why did you try that?

REYNOLDS: I tried it because everyone was talking about it. And there was very little science about whether it was a good idea or a bad idea. It's certainly a very popular idea, and a lot of people are now trying barefoot running without preparation, without knowledge of what happens when you take off your running shoes. And I was one. And what often happens is exactly what happened to me - which is that you almost immediately hurt your Achilles tendon.

GROSS: Is that because of the pressure, or the position of the foot?

REYNOLDS: Well, it's because - many people have heard that we are born to run, and that may or may not be anthropologically accurate. But we definitely have been brought up to wear shoes, and your body adjusts to what it is used to. So every muscle in your leg, every tendon, every ligament is used to how you land with shoes on. If you've been doing that for 40 years - which many of us have, if we're 40 - then your body is very used to that movement - to how you hit the ground with shoes on. The forces of the - of hitting the ground move up your leg in a very specific way.

You take off your shoes and even if, in theory, it's healthier, you're not used to it. And most of us who try barefoot running - and this is quite common - take off our shoes and do the same amount of running as we did with shoes on. The result is, our legs are not ready for it. The tissues, the tendons are not ready; and injuries are very common.

GROSS: Have you recovered yet?

REYNOLDS: Not completely. But I have returned to wearing shoes.

GROSS: So are you running again yet?

REYNOLDS: I am. And I'm running slowly. I'm running carefully. I'm running a little smarter, and that's certainly something that all runners need to be aware of - is, if you hurt yourself, you then have to be a little smarter. The single biggest risk factor for a running injury is a prior running injury. So if you've hurt yourself in the past, you probably need to change a little bit about how you run. You may need to warm up a little more. Some people like to switch to trails. There's not actually much science showing that the surface matters, but it definitely matters how many miles you do. And I'm running a fewer miles now, than I was.

GROSS: Now, what about the pros and cons of running when it comes to hips and knees?

REYNOLDS: Well, the science is very encouraging - in terms of both, as a matter of fact. There's a very strong myth that running will ruin your knees. And anyone who has run for as many years as I have has had people say to them, you're going to ruin your knees. Well that, scientifically, is just not true. The science actually shows that if you have a healthy knee to start with, running tends to increase the amount of cartilage that you produce. It prompts the cartilage cells - which are the shock absorbers in your knee - it prompts them to divide and produce more cartilage. So in theory, running is actually healthy for your knees.

There have been some very good studies showing that people with healthy knees, who run for decades, have no greater incidence of arthritis than people who don't run. The problem comes in if you've ever had a knee injury - and especially if you've ever torn your ACL, the little ligament that helps stabilize the knee. And ACL tears are very, very common. They're very common among young athletes nowadays. And what appears to happen is if you've ever torn your ACL, your knee is unstable. When you run, you start rubbing one part of the knee against another. You rub away cartilage. And so if you've had a prior injury and run, you can develop knee osteoarthritis very quickly; certainly, within a decade.

The same - very same process appears to happen in the hip. The hip is really important to running, and many people ignore it. It starts to hurt; they ignore it, and keep running. Again, if you have an unstable knee joint and run on it, you will probably cause arthritis. If your knee is healthy and you run on it, it will be good for the knee. It's a rather unfortunate catch-22.

GROSS: Let's talk a little bit about running shoes - and walking shoes, too. Some of the common wisdom about running shoes, apparently, is being disproven.

REYNOLDS: Yes. As in so many things, when they are actually put to the test in a laboratory, many of our beliefs about running shoes are being overturned. Many of us have been told we pronate a lot - that means our foot turns in - and that we need to stop that. There was a vogue for motion-control shoes, which are fairly heavy running shoes with all these features that control how your foot moves and essentially, tried to keep it from moving. The science is now suggesting that that doesn't help, and probably hurts. There are some very good studies showing that people who wear heavy motion-control shoes tend to get injured more often than people who wear any other type of shoe. It doesn't matter if they do pronate, or if they don't pronate. They get injured more if they wear a heavy running shoe.

GROSS: Is that because of the weight, or because of the control? Or both?

REYNOLDS: Almost certainly - it's not completely clear yet, but it almost certainly is because it keeps your foot from moving the way it actually should. Our foot is a beautiful instrument. It's got all of these bones and tissues that are designed to move and stabilize our body. When you encase it in this big, heavy brick of a shoe, what you do is, you take away all of the ability of the foot to stabilize your body.

That's why many people believe barefoot running is great for you. And for some people, it may be really good. It does allow the foot to completely control how your body is stabilized against the ground. For many of us, a much more lightweight shoe, something that protects our foot from the ground, that gives us a little bit of cushioning - whether we walk or run - does seem to be the best compromise between these really heavy, motion-control running shoes and going barefoot.

I now am starting to run in a - sort of a racing flat shoe, which is very light but it gives me a little bit of support; and definitely, my Achilles tendon doesn't hurt as much.

GROSS: So does this have any implications for orthotics?

REYNOLDS: The science on orthotics is very mixed, which is quite interesting. There's another, very entrenched myth that orthotics will keep people from getting injured; that if you go and see someone and they fit you with a customized orthotic, that you can run or walk or do any sort of exercise, and you'll never hurt yourself.

GROSS: And you'll never develop plantar fasciitis. That's another thing.

REYNOLDS: Exactly. Well, it's just not true. When they actually put people in custom orthotics or over-the-counter orthotics or nothing, there's very little difference in the injury rates. There seems to be a pretty strong placebo effect. People who get custom-made orthotics think that they're going to get less injured. Perhaps that will keep some of them from getting injured. But there's not very good science that orthotics will actually protect you from something like plantar fasciitis, whereas that is one instance where stretching almost certainly will help. Plantar fasciitis is caused by shortening of the tendon that runs under your foot and up your leg. And that, you probably need to stretch, especially as we get older.

GROSS: So in talking about shoes and orthotics, we should talk about high heels. You had a column about that recently. And what are some of the things that you learned about the stresses put on the foot, and the leg, from high heels?

REYNOLDS: Well, high heels are essentially a very exaggerated version of shoes. Most of us wear shoes - if we don't wear heels - that have some heel, but not a lot of heel. Even wearing shoes with a small amount of heel, it does affect the tissues in your leg. If you increase that heel, you exaggerate those effects.

What you start getting is a pretty significant shortening of the Achilles tendon. You get changes in all the tissues that run through your foot. You get changes in how your foot is oriented to the ground. If you wear high heels for five or six hours a day - and I don't know how anyone does, but they do - you pretty dramatically change how your foot is oriented.

And then, when you take high heels off, your foot is not ready for that. It honestly does not know how, essentially, to come into contact with the ground. Women who wear high heels all the time and then walk without them, walk completely differently than women who do not wear heels. And they probably increase their risk of a whole host of injuries.

GROSS: What's the difference between how women who frequently wear high heels walk, compared to those who don't?

REYNOLDS: Well, women who frequently wear high heels - again, the Achilles tendon shortens, and that changes how forces move up your leg. Your foot moves differently with each stride that you take. You can't move the forces as efficiently up your leg, so you get more forces moving up through the tendons than you would if you did not wear high heels.

If you don't wear high heels, your foot impacts the ground in a way that makes the forces move up through the bones, which are much better able to handle those forces. So if you wear high heels and then you walk without them, you get more forces moving up through the very soft tissues in your leg, and that definitely increases the chance of injury.

GROSS: You know, I sometimes ask somebody - ask a woman, like, gosh, how do you wear high heels like that? And they'll say to me, well, I'm actually more comfortable wearing heels than wearing flats. And from what you're saying, it sounds like it's because their foot is so trained to wearing heels, that it's difficult for the foot to adjust to contact with the ground.

REYNOLDS: Yes. That's definitely true. It actually is uncomfortable. Because you have a shortened tendon, it will feel tighter when you walk barefoot, or even in flats, if you are used to wearing high heels. So if you have been wearing high heels for years and years and decide that you want to go to flats, then you need - as with someone switching to barefoot running - you need to do it gradually.

You need to retrain the tissues in your leg to walk differently. And it will take some time. But it will definitely, ultimately be healthier for your leg.

GROSS: So let's talk about dealing with muscle soreness, the kind of soreness that can set in with overexertion or with, you know, a rigorous workout routine.

I was surprised to read in your book that taking a non-steroidal anti-inflammatory - you know, ibuprofen, something like that - can help you with the pain in the short term, but it's not necessarily going to help you with healing and, in fact, it might be counterproductive.

REYNOLDS: That actually surprised me. I hang around with a lot of athletes, and there are many athletes who take that non-steroidal ibuprofen every day. They take it before they work out because they hope that it will have a prophylactic effect; that it will keep them from getting sore after they work out.

And many professional athletes take three, four of these ibuprofen pills before every match, before every workout. The science actually shows that ibuprofen blunts the training response. It actually makes it harder for your muscles to adjust after exercise. So you actually get a little less muscle healing, and you get less muscle adaptation.

So if you take ibuprofen to try and keep yourself from getting sore, what you are doing is - probably, ultimately - increasing the chances you will get sore because your muscles are not as strong, not as well-adapted.

GROSS: Now, this doesn't apply to, say, the effects of ibuprofen in bruising.

REYNOLDS: No. Ibuprofen - what ibuprofen does really well is if you have actually hurt yourself - say, you sprained your ankle; you actually fell over and, as you said, bruised something - it will decrease swelling, and it will decrease pain. If you have an acute injury then, yes, that's probably what it's good for. If you are taking it to try and combat sore muscles, it's almost certainly a bad idea.

GROSS: So if the research says that ibuprofen isn't necessarily going to be helpful, it might be harmful in helping with sore muscles after a workout, what about icing? A lot of people like to ice after exercise.

REYNOLDS: There's quite a bit of research that suggests that it does not, in any way, speed the healing of muscles. It does make them feel a little better, and that can have both good and bad effects. If your muscle feels better and you've just had a hard workout, you may say huh, I can work out hard again tomorrow. That will not be effective. The most effective way to recover from a hard workout is to get a little bit of rest.

That actually allows the muscles to heal themselves, to adapt, to become stronger, to be ready for another workout - maybe the day after tomorrow. If you want to use ice, bear in mind, you still need to rest that muscle even if it feels a lot better.

GROSS: What do you do for muscle and nerve pain?

(SOUNDBITE OF LAUGHTER)

REYNOLDS: Not work out very hard. I actually do not run, certainly, as hard as I did when I was in my 30s. And one, very easy way to avoid having to recover a lot is not to work out super hard. If you do, in fact, work out hard enough to be sore, the best thing you can do is plan to either take the next day off or certainly, go easy.

There's very mixed research about whether massage works. I love massage, so I will continue to get massages whether they actually speed healing or not. And there's some evidence they might; there's some evidence they might not. If you like them, can afford them, by all means get a massage.

GROSS: Gretchen Reynolds writes the "Phys Ed" column for the New York Times blog Well. Her new book, about the latest research on exercise, is called "The First 20 Minutes." You can read an excerpt on our website, freshair.npr.org, where you can also download podcasts of our show. And you can follow us on Twitter @nprfreshair, and on Tumblr at nprfreshair.tumblr.com.

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