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!

Is leisure-time physical activity irrelevant?

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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Here’s a great example of how two people can look at the same data and reach totally opposite conclusions. Over at Obesity Notes, Arya Sharma just blogged about a new study surveying what types of activities (leisure, occupational, household) burn the most calories for people. The title of the post: “Why Leisure-Time Physical Activity is Irrelevant.” He reaches this conclusion because the study found that leisure-time physical activity accounts for at most 10 percent of total energy expenditure, even for the most active people.

To explain why I find this logic to be a bit strange, let me make an analogy. Let’s say we’re debating why kids these days no longer know how to do long division. A study comes out saying that only 10 percent of elementary schools currently teach long division. Possible conclusions:

  1. So few kids receive long division instruction that teaching is clearly irrelevant to their long-division ability (or lack thereof).
  2. The results are consistent with the theory that the almost total lack of long division instruction may contribute to kids’ observed inability to do long division.

To me, it seems like Dr. Sharma is choosing the first option. Now, there’s plenty in his post that I agree with, particularly the suggestion that we should emphasize things like active transport that use energy in constructive, goal-directed ways. But the blog post has a strong current of antipathy toward the whole concept of exercise that I find surprising. For example:

[W]e have originally evolved the ability to be physically active primarily to hunt, gather, fight, flee and reproduce. The notion that any reasonable person would actually engage in a significant amount of ‘non-utilitarian’ (read: useless) physical activity beyond early childhood… is something that physical education enthusiasts (and governments) would wish for, but nature failed to put into our genes.[…]

Yes, there is a small proportion of the population, who (strangely enough) continues to enjoy leisure-time physical activity well into adulthood. The vast majority, however, prefers to much rather spend their leisure time reading, playing a musical instrument, engaging in arts and crafts, or simply lying on the couch watching professional sports. This is perfectly reasonable and completely normal human behaviour.

I understand that Dr. Sharma is, to an extent, simply counterbalancing the relentless (and misplaced) societal message that tells obese people that they’re abnormal freaks who lack enough self-discipline to take the “simple” steps like exercise that would help them lose weight. But I find it absolutely baffling that he’s arguing, on the one hand, that evolution dictates that we stop physical play after adolescence, but on the other hand suggesting that we’re wired to enjoy mastering a musical instrument (a highly cognitively and sometimes physically demanding task) or watching the very sports that apparently cease to have meaning for us when we become adults. The net result is that, next time I see Dr. Sharma quoted on the question of whether exercise can play a role in preventing weight gain, I won’t be able to avoid the feeling that his answers are coloured by a deep personal dislike of exercise in addition to his reading of the research.

And there’s another point, too. Dr. Sharma talks about “policy changes” and “workplace initiatives” to promote things like active transport, which he views as far superior to  “useless” exercise. But to me, that seems like a false dichotomy. If I have the option of taking the subway to work, but a policy initiative “encourages” me to bike instead, how is that different from voluntary exercise? In both cases, I’m choosing to burn calories that I don’t have to burn, because I believe I will derive a benefit from doing so. Is evolution really wiring me to abhor biking if I head north along the Humber River trail, but to love it if I head east toward downtown along the subway line that could carry me there much more quickly and effortlessly?

And a final thought. Let’s distinguish between what’s “easy” (or what Dr. Sharma would consider “normal”) and what may or may not be causal or contributing factors to obesity. Speaking purely hypothetically here, if a large, well-designed study were to show that two hours of moderately hard daily exercise prevented weight gain in 98% of people, Dr. Sharma might quite rightly say that this finding is irrelevant — after all, how many people will be willing to do that much exercise? But in that case, it would no longer be correct to argue that physical activity can’t prevent weight gain. The current moment in history that we’re living through is precisely the product of our having followed what’s easy/normal at every branch in the road. To move to a different place, we’re going to have to take a path of greater resistance. Whether that means banning cars, restricting processed foods, or exercising more than seems “normal” remains to be seen. But it’s no longer enough to say “I can’t do that, evolution won’t let me” — because that’s what got us here in the first place.

Do you need a bit of extra fat to stay healthy as you age?

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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This week’s Jockology column in the Globe and Mail tries to untangle conflicting data about whether being moderately overweight increases or decreases your lifespan:

It’s a surprising, subversive and very, very popular idea.

Over the past few years, several studies – including a 2009 analysis of Statistics Canada data – have suggested that being a bit chubby as you get older, far from being a health risk, may actually help you live longer. The extra weight, the thinking goes, could help cushion you from the inevitable slings, arrows and hip fractures of old age.

But the newly published results of a three-decade-long study of clean-living Seventh-Day Adventists in California suggest that you might want to go easy on those early-bird specials after all. When confounding factors such as skinny smokers were removed, the effects of extra weight were clear – and bad – even for those older than 75… [READ THE WHOLE ARTICLE]

The article is accompanied by a graphic by Trish McAlaster, which includes a bit of info on the recent study showing aerobic exercise targets visceral fat more effectively than strength training, which targets subcutaneous fat:

Obesity, delayed gratification and the Marshmallow Test

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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A new follow-up to the famous Marshmallow Test study on delayed gratification has just been published. Back in the 1960s, researchers tested a group of pre-school children on how long they could resist the temptation of an immediate reward (e.g. a marshmallow) in favour of a “larger, later” reward (e.g. two marshmallows). They followed these kids for decades, and found that the kids who were able to hold out the longest ended up less vulnerable to outcomes ranging from obesity to divorce to crack cocaine addiction.

The newest update, just published in Proceedings of the National Academy of Sciences (full text freely available here, press release here), with the subjects now in their 40s, confirms that the kids who were “high delayers” are still “high delayers,” and the kids who were “low delayers” are still “low delayers.” For the first time, they used brain scanning to determine that the high delayers showed greater activation in the prefrontal cortex while the low delayers had greater recruitment of the ventral striatum. This may reflect the differing use of of different “cold” and “hot” modes of cognition in choosing between competing impulses.

Anyway, I’m not going to go into great depth about the neuroscience here (as noted above, those who are interested can read the full paper freely). What caught my attention was the following quote in the press release:

“This is the first time we have located the specific brain areas related to delayed gratification. This could have major implications in the treatment of obesity and addictions,” says lead author Dr. B.J. Casey, director of the Sackler Institute for Developmental Psychobiology at Weill Cornell Medical College and the Sackler Professor of Developmental Psychobiology.

One of the interesting debates that I’ve become more attuned to in following the blogs of people like Yoni Freedhoff and Arya Sharma is the tendency to ascribe moral failings — a lack of willpower and unwillingness to make the “right” choices — to obese people. Dr. Sharma frequently argues that “Eat Less, Move More”-type advice is useless for losing weight, because it fails to understand the “countless ways in which the psychoneurobiology, energy physiology and metabolism in anyone who has lost weight” drive you to regain that weight.

So in this picture, does increased power of delayed gratification have any role in treating or avoiding obesity? Or are the biological imperatives too strong for anyone’s self-control? Dr. Sharma had a very interesting post a couple of weeks ago about the role of personal choice in weight loss, responding to a recent paper in the Journal of the American Dietetic Association. He doesn’t reject the role of impulse control in weight loss — in fact, he suggests it should be considered:

Recognising and fully acknowledging how the brain’s neural circuitry that underlies these behaviours interacts with (and is thus ultimately responsive to) environmental situations and cues can perhaps provide a far more realistic and effective counseling strategy.

Of course, losing weight and avoiding weight gain in the first place are two distinct questions — and in the long term, any success we have in tackling society’s growing levels of obesity will probably come from helping future generations avoid obesity in the first place. The Marshmallow Test data does tell us something interesting: that you can predict who’s most likely to become obese based on tests of brain function in pre-school. That has nothing to do with resting metabolic rate, aptitude for sports, or even what they’re being fed at home.

Obviously, this trait isn’t the root of the problem. Presumably humans have always been born with varying degrees of delayed gratification; it’s only in our modern society that low delayers are at risk of obesity. This is consistent with the idea of an “obesogenic environment” — a world with a copious oversupply of calorie-dense food, convenient labour-saving devices always available, ubiquitous advertising to tempt us into taking the first marshmallow.

But still… it suggests that choices matter. I realize this starts to sound like a moral judgement (i.e. obese people must have made the “wrong” choices), but I don’t mean it that way. In fact, the Marshmallow Test tells us these choices are, to some extent, hardwired into us. But by acknowledging the role of choices, and understanding how and why the “wrong” choices are made, perhaps we can increase our odds of making the right choices. Dr. Sharma suggests a few ways this might work in the post I quoted from above. Another option: the idea of “brain training” is in disrepute right now, partly because it was so dramatically overhyped and oversold a few years ago, but maybe it’s something to consider. It’s a topic that comes up (peripherally) in the Jockology column I just wrote for next Monday’s Globe, and I’m looking forward to seeing more research on it.

Cardio vs weights for visceral and liver fat

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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A new study in the American Journal of Physiology revisits a very familiar topic — cardio versus weights — to determine which is better for reducing dangerous visceral and liver fat. A total of 155 subjects completed one of three eight-month training programs:

  1. Aerobic (AT): ~12 miles per week at 75% VO2max;
  2. Resistance(RT): 3 days a week, 8 exercises, 3 sets of 8-12;
  3. Aerobic/resistance (AT/RT): both the above programs combined.

At the end of the eight months, they used some pretty sophisticated tools to measure the outcomes, including CT scans to measure levels of visceral and liver fat. Here are some of the key outcomes:

And here’s how the researchers sum up the findings:

First, a resistance training program–even a very substantial one–did not significantly reduce body mass, visceral fat, liver fat or ALT liver enzyme levels. RT also did not reduce total abdominal fat, nor did it improve fasting insulin resistance. Second, in contrast to RT, a typical vigorous AT program resulted in significant reductions in visceral fat, liver fat and abdominal subcutaneous fat, and also led to improvements in circulating ALT and HOMA (fasting insulin resistance).

The results aren’t too surprising: as the researchers note, this particular aerobic training program likely burned about 67% more calories than the resistance program. It does seem a bit strange to me that adding resistance training to the aerobic training seems to make things worse rather than better — but the overall analysis in the paper says that AT and AT/RT are statistically indistinguishable. In other words, the weights add nothing. Don’t get me wrong: weights are useful for a lot of things, and this study was only testing a few specific outcomes. But on those outcomes — and they’re very important ones, particularly if you’re overweight — cardio trumps weights.