Treadmill Test Predicts Long-Term Health

Here’s the headline result from a study in JAMA Internal Medicine: For each additional minute subjects lasted on a treadmill test when they were young (18 to 30), they were 15 per cent less likely to die during the 27-year follow-up period, and 12 per cent less likely to develop heart disease.

So does this mean that if you last seven minutes on the test you’ll live forever?

No, it does not. Still, there are a few interesting points to note about the study, which was a big collaboration started in the 1980s in parts of America.

The first key point is that aerobic fitness can predict health outcomes even among young people, who generally don’t have any heart disease yet. There’s lots of evidence that higher fitness is linked to lower cardiovascular risk in middle-aged or older people, but it wasn’t necessarily obvious that being fit when you’re young would make much difference. Importantly, some of the subjects were retested seven years after the first test, and those who’d lost more than a minute on the treadmill test saw their risks climb again.

Another interesting point is that the data didn’t show any link between fitness (as measured by the treadmill test) and “coronary artery calcification,” which is a measure of how much calcium is building up and hardening your arteries. In other words, whatever cardiovascular benefits you get from being fit, it’s not that your arteries accumulate less calcium (at least in this relatively young group).

Instead, as an accompanying commentary in the journal points out, fitness seems to have other heart benefits that aren’t fully understood. Greater fitness usually leads to better cholesterol profile, lower blood pressure, and reduced risk of diabetes, all of which reduce your risk of heart disease. But if you add up those factors, you only explain about 60 per cent of the observed heart benefits of fitness—the other 40 per cent remains a mystery.

There’s some evidence, for example, that exercise affects what type of plaques build up in your arteries. You’re more likely to develop relatively stable, calcium-rich plaques that are less liable to rupture and cause a complete blockage. These subtle differences aren’t captured by measures like the coronary artery calcification score.

It’s worth remembering that “fitness” and “exercise” aren’t synonymous. Some people are fitter than others, independent of how much exercise they do. How much of the health boost observed here was the result of being active, and how much was simply the result of good genes? This study can’t answer that—but it suggests that, whether it comes easy or you have to work at it, being fit is a good thing.

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