How much exercise is too much?

A study of Tour de France cyclists between 1930 and 1964 finds they live longer than matched controls.

A little bit of exercise is good for you, but too much is bad for you. That seems to be a fairly widespread societal view — certainly anyone who trains seriously as a runner or cyclist or other endurance athlete is familiar with all the comments about how training so much can’t be good for you. And to be fair, there has been some recent research that raises questions about whether running multiple marathons over an extended period of time can damage your heart.

So I was very interested to see a study, forwarded by Brian Taylor (thanks!), that just appeared in the International Journal of Sports Medicine. Spanish researchers decided to study the records of cyclists who rode the Tour de France between 1930 and 1964 — an example of “extreme” exercise if ever there was one — and see how long they lived compared to the general population. They focused on riders from France, Italy and Belgium (who comprised 834 of the 1229 riders for whom birth records were available), and they compared the longevity of those riders to the general population from their home country in the year of their birth. Here are the aggregate results in graphical form:

The trend is pretty clear. The age by which 50% of the population died was 73.5 for the general cohort, and 81.5 for the Tour de France riders — who, according to the paper, ride about 30,000 to 35,000 km per year (though I’d be surprised in the riders competing in the 1930s were training as hard as modern riders).

So what does this tell us? Well, as in any case-control study, there are plenty of limitations on the conclusions we can draw. First of all, this doesn’t prove that “extreme” exercise is better than “moderate” exercise. It may be that riding 30,000 km/year is significantly better than doing no exercise at all (or than doing the relative pittance that the average modern person does), but is still worse for you than riding, say, 10,000 km/year. But it’s pretty clear that extreme levels of aerobic training don’t shorten your life. As the authors put it:

In our opinion, physicians, health professionals and general population should not hold the impression that strenuous exercise and/or high-level aerobic competitive sports have deleterious effects, are bad for one’s health, and shorten life.

It’s also worth mentioning some potential confounding factors. The paper notes that former athletes tend to smoke less, drink less alcohol and have a healthier diet than the general population. Fair enough: these factors almost certainly contribute to the increased longevity of the riders. Again, the conclusion we can draw isn’t that extreme riding makes you healthier; it’s that it doesn’t make you less healthy.

What about genetics and selection bias? Maybe the Tour de France riders tend to be the type of lucky person with a great metabolism who’s destined to be healthy for his entire life no matter what he does, and it’s those great genetics that predisposed him to become a competitive cyclist. Again, not an unreasonable point. In response, the authors point out a 2010 British Journal of Sports Medicine paper in which researchers in Sweden compared the genetic profiles of 100 world-class male endurance athletes (“Olympic finalists or Europe/World Champions and Tour de France finishers”) with 100 matched controls. They looked at 33 “risk-related mutations and polymorphisms” associated with cardiovascular disease, hypertension, insulin resistance, cancer, and other major causes of mortality — and found no difference:

[T]he overall picture suggests that there is no evidence that elite male world-class endurance athletes are genetically predisposed to have a lower disease risk than non-athletic controls. Thus, the previously documented association between strenuous aerobic exercise undertaken by elite athletes and increased life expectancy is likely not biased by genetic selection.

Bottom line: if the question is “How much exercise is too much?”, I still think the answer is “Way, way more than you think.”

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