This article from the NYTimes cites evidence that the body gets used to having the same overall energy expenditure per day. Therefore if you switch from never running to running for half an hour each day, you'll likely be more languorous the rest of the day. Is this really true?
The article also points out that you can (maybe) get used to moving more. Rodents that had been subject to lots of exercise over generations get used to regular exercise, and will run around like crazy when they can't run on their mouse-sized treadmill. Presumably people in the long run can get used to having higher energy expenditure as well. But in the short run? Maybe, maybe not.
How does this relate to studies about the efficacy of exercise? If our bodies are only willing to move so much, why should we exercise? Are studies that find exercising leads to people losing weight somehow flawed? Two thoughts:
First, the hypothesis that bodies have a constant level of activity has not been tested with randomized control trials. A proper study to really test this would be to have a treatment group exercise more than the control group and then measure overall movement the rest of the day. The study looking at English school children is in particular a terrible study to draw any inference from, given that these children are coming from such different socioeconomic backgrounds.
Second, in randomized control trials, research has found that exercise--especially effective exercise--does lead to weight loss. For example, combining weights with high intensity interval training seem to be an effective way to shed pounds. The hypothesis is that high intensity interval training raises the metabolism (for the rest of the day), while perhaps the weights allow the body to devote any residual calories to muscle rather than fat.
One thing I wonder about: Why aren't there more exercise focused randomized control trials? It is easy to set these things up, and doing a RCT would be a quick and effective way to see what really works in exercise. With a little experimentation, we could possibly quite quickly find the ideal workout for all different body types.
Here are some possible issues:
(1) Researchers are often interested in the mechanism. Just trying different types of exercise routines doesn't get at the underlying metabolic and physiological mechanisms. Academic researchers may find studies that just test different exercise routines to be really boring.
(2) These studies are not really that easy or cheap to run: You have to pay people to participate. And you have to make sure they stick to the exercise regime. And you have to make sure the study is ethical, which sometimes takes quite a bit of effort to prove.
(3) Such studies also take time. This would be especially true for any RCT that would test the long-run treatment effects of a particular type of exercise. And lots of time means that the researcher also needs to have lots of money.
(4) Drug studies have a lot more money behind them. I doubt that there is some grand conspiracy here, but on the other hand markets matter: A company like Pfizer has a lot more interest in testing a drug that they can patent and sell than an exercise routine that they cannot patent and sell. Even if patenting was possible, they would have a hard time stopping people from sharing that routine with their friends and the internet.
Is there any study out there that compares the number of different types of RCTs? It would be interesting to see how these numbers respond to macroeconomic shocks and government funding cycles.
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