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Fitness vs. fatness, again

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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Another study weighs in on the question of whether fitness or fatness is a more important marker of health (abstract here, press release here). This is a nice, clear one. The researchers followed 14,345 men (with an average age of 44 at the start of the study). They did two detailed physical exams just over six years apart (on average), then followed the men for another 11 years to see which ones died, and why.

Basically, there are two variables of interest:

  1. Did the men lose weight, gain weight, or stay stable between the two exams?
  2. Did the men lose fitness (as measured by a maximal treadmill test), gain fitness, or stay stable?

The result: those who maintained or improved fitness were less likely to die by ~30-40% compared to those who lost fitness — even when you control for factors like BMI. Obvious and expected.

But what about weight? As you’d guess, those who gained weight were more likely (by 35-39%) to die of heart disease than those who lost weight or stayed stable. BUT if you take into account changes in fitness, then the effect of changes in weight almost disappeared. So this is further support for Stephen Blair’s argument that it’s fitness that matters, not fatness, when it comes to predicting health (and Blair is, indeed, one of the authors of this paper). As the press release puts it:

“This is good news for people who are physically active but can’t seem to lose weight,” said Duck-chul Lee, Ph.D. […] “You can worry less about your weight as long as you continue to maintain or increase your fitness levels.”

But let me add one clarification. Whenever this topic comes up, I often hear from people who say something along the lines of “See, BMI is meaningless! This proves that doctors should never even measure weight, because it doesn’t predict health.” Not quite. Let me reiterate: those who gained weight in this study were 39% more likely to die of a heart attack than those who lost weight. The reason weight gain doesn’t stay as an independent predictor of death is that those who gained weight also (on average) lost fitness, and those who lost weight also (on average) gained or maintained fitness.

So the very important message that this study reinforces is that it’s fitness that matters most. Keep exercising even if you don’t see changes in your weight, and you’ll be gaining extremely important benefits. But don’t interpret it to mean “it doesn’t matter if I gain weight, because weight is meaningless as a health marker” — because there’s a decent chance (though it’s certainly not guaranteed) that if you’re gaining weight, you’re also losing fitness.

(One final caveat: as the press release notes, 90 percent of the men were either “normal weight” or “overweight” — i.e. BMI under 30. So you can’t assume that the same lack of problems would hold true for the “obese” category with BMI over 30.)

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Which childhood activities predict healthy adulthood?

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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Encouraging kids to be more active is one of those motherhood-and-apple-pie goals that pretty much everyone sees as an excellent idea. Still, it’s worth asking: do the kids who are most active grow up to be the adults who are most active? And perhaps more importantly, which types of childhood activity (school phys ed? sports? unstructured play? walking or biking to school?) are most effective at establishing lifelong habits of physical activity?

Researchers in Australia just published a big study on the British Journal of Sports Medicine that followed up on 2,201 kids who had completed a detailed physical activity questionnaire way back in 1985, when they were between the ages of 9 and 15. The goal was to figure out whether and how “frequency and duration of discretionary sport and exercise (leisure activity), transport activity, school sport and physical education (PE) in the past week and number of sports played in the past year” when they were kids influenced their activity patterns as adults between the ages of 26 and 36.

Depending on how you look at it, the results are either very simple or very complicated. You can delve into all the nitty-gritty details of which childhood factors seem linked to which adulthood factors — and find puzzling and seemingly contradictory trends like this:

Higher levels of school sport among older males were associated with a 40% increase in the likelihood of being in the top third of total weekly activity in adulthood, but with a 40% lower likelihood among younger males.

Does this mean that school sport is bad for 9- to 12-year-olds and good for 13- to 15-year-olds? Probably not. As discussed earlier this week, when you search for links between large numbers of variables in a big collection of data, you’ll always find some relationships that appear statistically significant but in fact have little or no meaning. When you look at this data as a whole, there are a few “significant” associations, but there’s no overall trend, as the researchers acknowledge:

[F]ew associations were evident, most were relatively weak in magnitude and, for some activities, inconsistent in direction.

In other words, if you take a group of 12-year-olds and look at how active they are, you’ll have very little ability to predict which of those kids will have healthy, active lifestyles 20 years later. This is a bit of a bummer, because it makes it harder to decide exactly what types of physical activity are most useful for forming lifelong activity patterns. But don’t make the mistake of thinking that this implies that school phys ed (and other childhood physical activity) isn’t useful! Phys ed for 12-year-olds may not produce healthy 30-year-olds, but it sure as heck produces healthy 12-year-olds — and that’s a worthwhile goal on its own.

And hey, there’s also the fact that (as Gretchen Reynolds wrote about in the New York Times last week), a little bit of physical activity makes you perform better on tests. What kid wouldn’t want a boost of brain-derived neurotrophic factor coursing through his veins and boosting his memory as he heads back to math class?

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Actual data on foot strike patterns

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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The debate rages on about how your foot should land when you’re running — but we still know remarkably little about how people’s feet are currently landing in the real world, outside of biomechanics laboratories. Pete Larson (of Runblogger fame) has a new paper in the Journal of Sports Sciences that offers some interesting data. It’s a very straightforward study: he (and his undergrad researchers) hung out at the 10K and 32K marks of the 2009 Manchester City Marathon with a high-speed camera, and filmed the runners going past. Then they went back and classified the foot strikes into three categories as illustrated here:

At the 10K mark, he got data for 936 runners who were doing either the half or full marathon. The results:

  • rearfoot: 88.9%
  • midfoot: 3.4%
  • forefoot: 1.8%
  • asymmetrical (i.e. different with right and left foot): 5.9%

It’s worth noting that virtually none of the runners were barefoot or wearing Vibrams — this was 2009, before the frenzy really started. Larson collected more data this year, so it will be interesting to see what (if anything) changes when that data is analyzed.

At the 32K mark, it was just marathoners, and Larson was able to positively identify 286 runners at both the 10K and 32K marks. Of these runners, 87.8% were rearfoot striking at 10K, and 93.0% were rearfoot striking at 32K. Basically, some of the runners who weren’t rearfoot striking initially got tired and settled into a rearfoot gait. There were no forefoot strikers left at 32K. To me, this is the most interesting avenue for further research: can people who switch to a forefoot strike maintain it all the way through a marathon? Do you have to grow up barefoot to develop that strength, or can it be acquired in a few years?

One last point: no significant relationship between race times and foot strike (though the number of non-rearfoot strikers was so small that any relationship would have been hard to find). Anyway, great to see some hard data, and I’m sure we’ll see a lot more like this in the years to come.

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Cherry-picking, statistical adjustment, and fishing expeditions

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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My Jockology column in this week’s Globe and Mail takes a look at three questions:

  1. How do cigarettes help marathoners run faster?
  2. Why does eating red meat cause car crashes?
  3. Does caffeine cause breast cancer?

In each case, I analyze studies that seem to “prove” these surprising findings, and identify the errors (cherry-picking data, inadequate statistical adjustment, and fishing expeditions) that lead to these conclusions. Basically, it’s a “how to assess medical research” primer. Read the whole thing here.

(Hat tip to Travis Saunders for his blog post at Obesity Panacea about the smoking study.)

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“Reduced intensity” HIT: the Flutter of exercise

THANK YOU FOR VISITING SWEATSCIENCE.COM!

My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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Anyone remember this Twitter spoof video from back in 2009, when Twitter was just catching on? It’s all about “Flutter,” which “takes microblogging to the next level” by restricting the length of each message to 26 characters instead of 140 characters. Nanoblogging, they call it.

I couldn’t help thinking of this when I read this new study in the European Journal of Applied Physiology about “reduced-exertion high-intensity interval training” (REHIT). Over the last few years, high-intensity interval training (HIT) has gotten a lot of attention as a time-efficient way of getting many of the health benefits of aerobic exercise. There are various protocols — the classic is four to six 30-second sprints with 4:00 easy jogging or cycling to recover between each one; another common one is alternating bouts of 1:00 hard with 1:00 easy. These workouts seem to be highly effective at improving traits like insulin sensitivity. But there’s a catch, according to the authors of the new study:

However, whilst these observations [about HIT] are interesting from a human physiological perspective, their translation into physical activity recommendations for the general population is uncertain for two reasons. First, the relatively high exertion associated with ‘classic’ HIT sessions requires strong motivation and may be perceived as too strenuous for many sedentary individuals. Second, although a typical HIT session requires only 2–3 min of actual sprint exercise, when considered as a feasible exercise session including a warm-up, recovery intervals and cool-down, the total time commitment is more than 20 min [gasp!], reducing the time efficiency. Thus, there is scope for further research to determine whether the current HIT protocol can be modified to reduce the levels of exertion and time-commitment while maintaining the associated health benefits.

In other words, the “140 character” version of exercise is still too damn long, so we need to shorten it to 26 characters!

So here’s the protocol they used. The subjects (29 sedentary young men and women) did three workouts a week for six weeks. Each of these workouts was exactly 10 minutes long, and consisted almost exclusively of “low intensity” cycling, at 60 W. This is very easy. During each 10-minute workout, the subjects incorporated two 10- to 20-second hard sprints. That’s it. Lo and behold, the men in the REHIT group increased their insulin sensitivity by 28%. Strangely, the women didn’t improve — it’s not clear why there was a gender difference. It may be that the very short sprints are most useful for men, who tend to be more powerful and thus are able to burn through more glycogen in a short time.

Anyway, there you have it: REHIT, the Flutter of exercise. I have to admit, part of me finds this a little funny. Soon we’ll be doing studies to show that, if you’re really and truly unfit, just blinking your eyes will allow you to make “measurable gains” in fitness parameters. On the other hand, the barriers to getting people to exercise really are tough to beat. I’m always encouraging my parents to do a little HIT rather than just stick to low-intensity activity — and they do, but they’re rarely motivated to spend more than 10 minutes in total. So it’s encouraging — and useful — to know that even a very minimal bout of high intensity will help. In the end, though, the message is pretty much what we already knew: every little bit helps — but more is better.