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Is leisure-time physical activity irrelevant?

October 13th, 2011

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.

  1. Hilary Curtis
    October 13th, 2011 at 18:21 | #1

    I think there’s another flaw in the argument. I can only see the abstract to the original article, but it’s scarcely surprising that work accounts for the bulk of physical activity-related energy expenditure – the obvious reason being that work typically accounts for 30-40 hours a week ie 18-24% of total time.

    You have to be fairly a serious fitness freak to spend even 7 hours a week (4%) in leisure-time physical activity so it’s actually quite impressive that this can contribute as much as 10% of total energy expenditure (and presumably more than 10% of activity-related energy expenditure after subtracting off resting metabolism).

    What this says to me is that leisure-time physical activity tends to be rather intense. So a relatively small increase in time doing it would have a large marginal effect on energy expenditure. I’d say that’s a pretty strong argument in favour of active leisure.

  2. Phil Koop
    October 13th, 2011 at 18:35 | #2

    My first reaction on reading Sharma’s post: on what planet is marathon running representative of leisure-time physical activity? It’s easy to describe physically active people as a “vanishingly small proportion of our species” when you anchor your references so tendentiously. But back on earth, about half my office colleagues play rec hockey. And when I was growing up, spending a pleasant Saturday hiking or skiing in the Gatineaus was a perfectly normal family activity for all ages.

    My second reaction was to his laundry list “reading, playing a musical instrument, engaging in arts and crafts …” It is hardly surprising that if you have a long list of things, then any one item will be rare compared to the rest in aggregate. But if I called cycling a “hobby” rather than “exercise”, how would it rank in frequency? And would Sharma then be willing to concede that less frequently occurring hobbies are not “normal human behaviour”?

  3. Jeepers
    October 13th, 2011 at 18:41 | #3

    If you choose to bike to work rather than bike as a leisure activity, you may be burning the same number of calories but you may not be doing it for the same reasons. You may bike to work because it’s a simple and convenient way to get to work. You may not be doing it to “get exercise”. For me, having chosen not to have a car, I can get to work by public transit or by bike (at least part of the year). It just so happens that biking takes approximately the same amount of time, while also saving me money, improving my mood, and helping me avoid being jammed together with strangers like sardines in a can. So I might choose to bike for those benefits, even without caring about the beneficial effect physical activity has on my health. As it happens, I personally do care about the physical activity aspect — I’m just saying that it may not be sufficient to motivate some people in and of itself. By biking to work I am also not giving up my leisure time to “do exercise”, as it takes the place of my commute. (I personally do other forms of physical activity in my leisure time, such as running and swimming, but I might not have had the time to train for a triathlon this summer if I had to do all that cycling in my leisure time as well.)

    I think I’ve read that most cyclists in Copenhagen and Amsterdam don’t bike to work for health or environmental reasons, but simply for convenience.

  4. alex
    October 13th, 2011 at 19:38 | #4

    @Hilary: Agreed!

    @Phil: Yes, the things that struck you are also what made me feel that I was reading an emotion-driven attempt to justify pre-existing beliefs, rather than a fair assessment of the evidence.

    @Jeepers: Yes, I certainly understand that active commuting, for example, is a far more attractive option than, say, slogging away on a stairclimber for most people. There’s no doubt that we can tweak our environment in many ways to encourage more physical activity. I just don’t agree that there’s a fundamental difference in character between “unnatural” physical activity done as a leisure-time activity and “natural” physical activity arising from deliberate choices NOT to take the easiest option. They’re different by degree, not by nature.

    To give a counterexample, I’m about to head across town to do a running workout with a bunch of old friends with whom I’ve been running for years. I haven’t seen them in months, since I’ve been out of town. It would be far more efficient for me to step out the door and do my workout in the park by my house. But the primary goal of this workout is as a social outlet for me, though I’m certainly aware of the fitness benefits. Motives are always mixed, whether we’re talking about active commuting or integrating other forms of physical activity into our leisure time.

  5. Seth Leon
    October 14th, 2011 at 16:31 | #5

    What is ‘unnatural’ is sitting at desk 40 hrs a week and I’m sure Dr. Sharma is familiar with the research in that area. It may be ‘completely normal’ to choose the easy option of sitting on the couch on the weekends, but combined with are current work environments it is certainly unhealthy.

    Our bodies are designed for regular exercise regardless of the mode (leisure or work comute). Our current culture requires most of us to find ways to compensate for our work lives. We should be encouraging all ways in which these healthy behaviors are pursued. Slapping the ‘unnatural’ label on leisure time exercise seems outrageous to me.

  6. BMan
    October 15th, 2011 at 01:52 | #6

    I’m not a big believer in worrying about what is natural or what we evolved to do since none of that applies to modern lives anyway (no food is the same as it was 10,000 years ago, we live in cities, with concrete, we drink clean water, we live in houses, we drive in cars and breathe in chemicals that didn’t exist, we have completely different stressors, etc, etc).

    What I do equate this situation to is training smart and training stupid (and obviously, which does better for you). If you are a stupid athlete training for say, a marathon, you might go out and run about the same distance everyday and with the same moderate effort everyday. If you are a smart athlete you probably do some of your workouts extremely hard and some extremely easy, with just a bit in between (and you also vary the distance and have a plan for many other factors as well). Now which would equate to the exercise you get purely from commuting and which would equate to the exercise you get from leisure time? Obviously commuting is going to be the same everyday – I realize that it doesn’t have to be, but most likely, for most people, it will be. Whereas in leisure time you are not only more likely to vary, but almost certainly will vary your effort levels and duration of exercise. You are also far more likely to do sprints and to go really easy. And that is far healthier for you.

    So, to me, it seems that exercise during leisure time is going to be far more beneficial for your health. (And I also suspect far better for your mental health, but that gets more complicated).

  7. Cesar Lasanta
    October 24th, 2011 at 15:13 | #7

    I think that Dr.Sharma is completely wrong about which we humans are prone to due to evolution.

    In my land (Aragon-Spain) run races have been traditional for centuries. Even my grandfather by mother used to run by money-even without race. For example, running from point A to point B in less than time X. And my father, who does no sport whatsoever and is by no means an ecologist, likes very much a walk during the very early hours of the day. Just for the joy of seeing the nature awake, just to put the legs on movement.

    I think that we are prone to physical activity. Moreover, we know that any physical capability which is not used, is lost. That means that we are prone to exercice EVEN IF USELESS. In a non-civilized enviroment, exercice is needed, but no always useful. Obviously.

  1. October 14th, 2011 at 21:41 | #1
  2. October 17th, 2011 at 14:06 | #2