Yoga vs. stretching for lower back pain

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As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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I tend to post a lot about studies that find no benefits from traditional static stretching. Does that mean stretching has no benefits? No — it just means that the benefits are hard to quantify. So to be fair and balanced, I figured I should mention this recent study from the Archives of Internal Medicine, which suggests that stretching may be helpful for lower back pain (press releases here and here).

The study was actually designed to test whether yoga helps back pain. They compared a 12-week yoga program to 12 weeks of stretching (chosen to have a similar level of physical exertion), or 12 weeks reading a self-care book. Both yoga and stretching were better than reading the book at improving pain and function; there were no differences between yoga and stretching.

Now, I can’t help pointing out that the study isn’t immune to placebo effects. The assessments of pain and function were done with telephone interviews, and relied on subjective reports from the patients. And let’s be honest: the suckers who were randomized into the “self-care book” group knew darn well that they got the short end of the stick! So I don’t view this as strong evidence of a mechanistic relationship between stretching and back pain (i.e. that the back pain is caused by tightness in some specific muscle, and stretching releases the pressure to eliminate the pain). But that’s kind of beside the point. The stretching made people feel better — and for a very simple, low-cost, low-risk, uninvasive intervention (unlike, say, surgery), that’s a good enough outcome.

Another reason for morning workouts: UV and cancer

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As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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Runners and cyclists (and walkers and open-water swimmers and so on) spend a  lot of time outdoors. Which is great — for me, that’s one of the big attractions! Still, that’s a lot of UV exposure, which is a bit worrying. But a neat and surprising study from researchers at the University of North Carolina, published in the Proceedings of the National Academy of Sciences, suggests that UV exposure in the morning is much less damaging than an identical dose of UV exposure later in the afternoon. This has nothing to do with cloud cover or sunlight intensity — it’s all about the body’s circadian rhythms.

The problem with UV light is that it damages your DNA; your body fights this ongoing damage by trying to repair the DNA. The levels of a key protein responsible for this repair process fluctuate during the day, with a maximum early in the morning and a minimum late in the afternoon. In contrast, the process of DNA replication, which can cause the errors in damaged DNA to spread, is slowest in the morning and fastest in the afternoon. So UV damage in the morning should be less likely to spread and more quickly repaired; in the afternoon, it’s the opposite. Here’s an illustration from the study’ s press release (you’ll notice that mice, which are nocturnal, have exactly the reverse pattern):

So does this effect have any real practical significance? Well, the researcher tested it on mice. They exposed two groups of mice to identical doses of UV radiation, one at 4 a.m. and the other at 4 p.m. The morning exposure group was five times more likely to develop skin cancer than the afternoon exposure group. (Remember that mice have the opposite cycle compared to humans, so that means morning is the best time to be exposed for humans.)

Is this sufficient evidence to tell people to switch up their exercise patterns? Not really. The researchers are now planning to directly measure DNA repair rates in human volunteers at various times, which would be another plank. For now, the timing of my workouts (which are, in fact, mostly in the morning) is dictated by lots of other factors — but it’ll make me worry a little less about the tan lines that I develop even when I’m running super-early in the morning. Now I just need a study that tells me that vitamin D production is maximized by morning sun exposure, and I’ll be all set!

Power Balance bracelets in placebo-controlled experiment

THANK YOU FOR VISITING SWEATSCIENCE.COM!

As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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I’m embarrassed to even report on this study — but just in case there are still any Power Balance believers out there, researchers at the University of Texas at Tyler have just published a placebo-controlled, double-blind, counterbalanced test of strength, flexibility and balance, in the Journal of Strength & Conditioning Research. They compared Power Balance bracelets to the same bracelets with the “energy flow distributing Mylar hologram” removed, and to nothing at all. And, believe it or not, they found no differences. For example:

And for all those who still swear that, when the salesman put the bracelet on their wrist, they really did do better on the balance test, it’s worth noting the University of Wisconsin pilot study (cited in the Texas paper) that found that in balance and flexibility tests like the ones used by Power Balance salespeople, you always do better the second time you try it, due to learning effects. So if you try the test first with the bracelet on, then with the bracelet off, you’ll “prove” that the energy flow actually harms your balance. (Or maybe that just means you had the bracelet on backwards…)

The activitystat hypothesis: do we have an exercise set point?

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As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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If you do a vigorous workout in the morning, will you be correspondingly less active for the rest of the day, so that your total physical activity ends up being the same as if you hadn’t worked out at all? That’s the basic gist of the “activitystat” hypothesis, which Gretchen Reynolds described in a New York Times article last week (thanks to Ed for the heads-up!). It’s also the topic of a pro vs. con [EDIT: had the links backward before -AH] debate in the current issue of the International Journal of Obesity (full text free available).

Reynolds describes several interesting studies that line up in favour of or against the theory, including one (from the same issue of IJO) that compared three British elementary schools with very different amounts of in-school physical activity. Here’s what that study found:

You can see that, for both “total physical activity” and “moderate and vigorous physical activity,” one group had much higher levels in school than the other two, but compensated by doing less outside school. On the surface, it seems like a pretty compelling argument in favour of the activitystat hypothesis.

My take: somewhere in the middle, as usual. It would be ludicrous to claim that the body doesn’t regulate physical activity based on previous exertions to some degree. Do a one-day study of “voluntary movement” among people who have run a marathon that morning, and of course you’re going to find that they chill out more. At the opposite extreme, it would be equally silly to argue that all people everywhere in the world do exactly the same amount of physical activity. Or that any given person’s physical activity stays essentially constant over long periods of time  — again, think of someone who goes from sedentary to marathon training: no amount of fidgeting or taking the stairs will add up to the exertions of 100-mile weeks. (For more examples of the role of environment in determining activity level, read the “con” commentary I linked to above. E.g. Nandi children in Kenya who grow up in the countryside are more active overall than Nandi city kids — an obvious result, but one that clashes with the activitystat idea.)

So the relevant question isn’t “Do compensatory mechanisms exist?” It’s “Do they matter, and are they insurmountable?” As lovely as the data from the British school study is, I don’t find it convincing. The school with the highest in-school physical activity was a fancy boarding school in the countryside, while the other two schools were urban. If the boarding-school kids play an hour of cricket in phys ed every day, the fact that they don’t choose to go play an hour after school doesn’t necessarily mean that the activitystat is limiting them. Maybe they just want to (or have to, depending on the other extracurricular requirements of the school) do something else.

One final point: it would be interesting to stratify those results based on the activity levels of the kids. Does the apparent activitystat mechanism apply equally to the most active and least active kids? Because if there are some kids who, left to their own devices, only get a total of 50 minutes of moderate/vigorous activity per week, then giving them 100 minutes a week in school is going to benefit them — and there’s nothing any activitystat can do to stop it!

Higher carb intake = faster Ironman finish

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As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)

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Here’s a graph, from a recent paper on nutrition during long (marathon and longer) endurance competitions, that’s worth a close look:

What do you see? A bunch of dots scattered randomly? Look a bit more closely. The data shows total carb intake (in grams per hour) by racers in Ironman Hawaii (top) and Ironman Germany (bottom), plotted against finishing time. It comes from a Medicine & Science in Sports & Exercise paper by Asker Jeukendrup’s group (with several collaborators, including Canadian Sport Centre physiologist Trent Stellingwerff) that looked at “in the field” nutritional intake and gastrointestinal problems in marathons, Ironman and half-Ironman triathlons, and long cycling races. The basic conclusion:

High CHO [carbohydrate] intake during exercise was related to increased scores for nausea and flatulence, but also to better performance during IM races.

So basically, taking lots of carbs may upset your stomach, but helps you perform better. It’s important to remember that gastrointestinal tolerance is trainable, so it’s worth putting up with some discomfort to gradually raise the threshold of what you’re able to tolerate.

Anyway, back to that graph: while it may look pretty random, statistical analysis shows a crystal-clear link between higher carb intake rates and faster race times, albeit with significant individual variation. Obviously there are some important caveats — it may be, for example, that faster athletes tend to be more knowledgeable about the benefits of carbs, and thus take more. Still, it’s real world data that tells us the people at the front of the race tend to have a higher carb intake rate.

One other point worth noting. The traditional thinking was that humans generally couldn’t process more than 60 grams of carb per hour. Over the last few years, thanks to multiple-carb blends, that threshold has been pushed up to 90 grams of carb per hour. In this data set, about 50% of the triathletes were taking 90 g/hr or more.

[UPDATE 10/26: Given all the comments below about the variability in the data, I think it’s worth emphasizing what should be a fairly obvious point. The only way this data would come out as a nice straight line is if Ironman finishing time depended ONLY on carb intake, and was totally independent of training, experience, talent, gender, body size, and innumerable other factors. This is obviously not the case, so we should expect the data to be very broadly scattered. What the statistical analysis shows is that, with p<0.001, faster finishers tended to have consumed carbs at a higher rate. There are many ways to interpret this data; one possibility is that, if your carb consumption is below average, you might wish to try a higher rate of consumption (e.g. 90 g/hr) to see if it helps.]