With most things, we understand the value of moderation. Light drinking makes you healthier; heavy drinking will make you less healthy. Calcium may give you strong bones, but you don’t want so much that you give yourself kidney stones. Even too much kale has risks.
But…exercise? Jogging. Surely there can’t possibly be such a thing as too much jogging, right?
A study published early in February made the claim that running too much was as bad for you as not exercising at all, which seems like a self-evidently absurd claim, unless people are running on the shoulders of interstate highways or through toxic waste dumps.
And having scrutinized the study, I am really dubious. Bear with me, because this is going to require a statistics explanation.
From the study itself: “The joggers were divided into light, moderate, and strenuous joggers. The lowest HR for mortality was found in light joggers (HR: 0.22; 95% CI: 0.10 to 0.47), followed by moderate joggers (HR: 0.66; 95% CI: 0.32 to 1.38) and strenuous joggers (HR: 1.97; 95% CI: 0.48 to 8.14).”
HR stands for hazard ratio. You want your HR to be small. All the joggers were being compared to a group of sedentary non-joggers: being a couch potato had a hazard ratio of 1. So a hazard ratio that’s in the form of a decimal is a good thing. They calculated that the light joggers had a hazard ratio of 0.22, and the moderate joggers have a hazard ratio of 0.66. The strenuous joggers had a hazard ratio of 1.97 which is shockingly bad.
But, okay: the second set of numbers in their writeup are the confidence interval. For light joggers, they say, “95% CI: 0.10 to 0.47.” What that means is that they came up with the number 0.22, and based on their statistical black magic they are 95% sure that the real number is somewhere between 0.10 and 0.47. For moderate joggers, they are 95% sure that the real hazard ratio is somewhere between 0.32 and 1.38.
If your eyes glazed over, here’s what you really need to know: a small confidence interval is like saying, “we’re pretty sure the dude we’re looking for is somewhere in the building.” A large confidence interval is like saying, “we’re pretty sure the dude we’re looking for is somewhere in the neighborhood.”
For the strenuous joggers, the confidence interval is 0.48 to 8.14. “That dude we’re looking for? We think there’s a 95% chance he’s somewhere in New York.” In the actual paper, they draw it out for you, and the confidence intervals for the moderate joggers fall almost entirely inside the confidence interval for the strenuous joggers. So, maybe strenuous jogging is worse for you — but that 95% confidence level they’re talking about should definitely not be applied to that 1.97 Hazard Ratio.
The reason why they are so uncertain is that there weren’t all that many strenuous joggers — forty — and over the course of the study, two of them died. No matter how good something is for you, it’s no guarantee that you won’t get hit by lightning, or cancer.
On the other hand, “too much running might not actually be good for you” is not actually a new finding. A study from 2011 found at least temporary heart damage following marathons. In 2014, a study was published finding an increase in coronary artery plaque among marathon runners. One of the authors, James H. O’Keefe, was also involved in the latest paper – it’s probably fair to say that the risks of excessive exercise are a personal hobbyhorse for him. And in 2013, a study on heart-attack survivors found that more running or walking was beneficial until participants hit 7.1 km of running or 10.7 km of walking daily, at which point more exercise created worse outcomes. And that paper was from James O’Keefe’s apparent professional nemesis, Paul Williams, who has spent decades researching how more exercise is better than whatever you’re doing right now.
The bottom line here is that we don’t really know. The latest study might show that too much running (by which they mean more than 4 hours a week) is bad for you. Or, maybe it just shows that two of their most avid runners were unlucky. Lots of running may give you artery plaque and wider arteries, making the plaque a non-issue.
The one thing we do know for sure is that exercising is a whole lot better for you than not exercising. So if the prospect of running a marathon is what motivates you to be active? Do it. And if you’d rather stick with an easy-going quarter-mile daily jog, do that, instead. Basically, you can find some science to have on your side either way. There is no science out there that will back you staying on the couch, though. At least not this week.
[Featured Image by Shutterstock]