Is leisure-time physical activity irrelevant?
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:
- So few kids receive long division instruction that teaching is clearly irrelevant to their long-division ability (or lack thereof).
- 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.