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Recently, while sifting through some of the excruciatingly detailed performance data he’d collected over decades as a Colorado-based triathlon coach, Alan Couzens noticed a pleasing symmetry. All else being equal, the amount of aerobic fitness his athletes lost by getting a year older was almost identical to the amount they gained by adding an hour per month of training time. Want to freeze the biological clock from one birthday to the next? Find a spare 15 minutes per week and fill it with running.
The long-haul practicality of this approach is debatable: after a decade, that additional training time would total 2.5 hours a week. But the underlying premise of what we might call the Couzens Immortality Quotient taps into a fertile area of debate. How much of the aging process is an inevitable slide into decrepitude, and how much is a result of not getting enough exercise?
That’s the question Johannes Burtscher of the University of Lausanne, along with colleagues in Switzerland and Austria, posed recently in the International Journal of Environmental Research and Public Health. By pooling the results of more than a dozen studies, the group reached an encouraging, quantifiable conclusion: only about half of the fitness losses suffered by endurance athletes as they get older are attributable to the passage of time. The other half can be chalked up to reduced training.
The standard gauge of aerobic fitness is VO2 max, which measures how quickly you’re able to breathe oxygen into your lungs, pump it through your arteries, and use it to help fuel muscle contraction. It’s expressed in milliliters of oxygen per kilogram of body weight per minute, and in young adults it typically hovers somewhere in the forties. After age 25, it declines by about 10 percent each decade, dropping more quickly in your sixties and seventies. Among endurance athletes, the numbers aren’t so predictable. Some studies find losses of 5 percent per decade; others as much as 46 percent. What accounts for the difference? The extent to which you continue training as you get older. After all, the fitter you are, the more you stand to lose.
The effects of ceasing training entirely seem to be similar in athletes of all ages. Your VO2 max begins to plummet within a few days of stopping exercise, and you might lose as much as 20 percent after 12 weeks. These losses are explained mostly by changes in how much blood your heart can pump with each beat; the good news is that the trend can be reversed fairly quickly when training is resumed. Other age-related changes, such as stiffening arteries, occur more slowly and are harder to undo.
How much of aging is an inevitable slide into decrepitude, and how much is a result of not getting enough exercise?
When Burtscher and his colleagues ran the numbers, they found that 54 percent of the variation in fitness loss by male endurance athletes was explained by differences in how much they trained. That number in women was 39 percent, but the scarcity of data for female subjects makes it impossible to tell whether there’s a real physiological difference between the sexes. Overall, the data fits with the observation that athletes who keep training at a fairly constant level over the years lose about 5 percent per decade—half as much as the typical nonathlete.
There are a couple of key questions raised by these findings. The first one: If you miss a year, or a decade, can you get back to where you were? Or is some of that fitness lost forever? There’s no research to suggest a solid answer, according to Grégoire Millet, one of Burtscher’s colleagues at the University of Lausanne. It probably depends to some degree on how much you trained prior to stopping, and for how long. The risk upon resuming would be that your bones and connective tissue are no longer prepared to handle a heavy load, making you more susceptible to injury.
Still, there are some encouraging hints in the literature. In 2020, researchers published lab data on Tommy Hughes, an Irish man who’d recently run an eye-popping 2:27 marathon at age 59. Hughes’s VO2 max was 65.4, more than twice what you’d expect from a largely sedentary man his age. Not surprisingly, Hughes was a former elite marathoner; he competed at the Barcelona Olympics in 1992. But he’d taken a 16-year break from running, starting again at the age of 48. We can’t know for sure if that pause hurt him—if it did, it couldn’t have been by much, given that he currently holds the world marathon record for the 60-to-64 age group, at 2:30:02.
The other question is how to maintain your training level as the years pass. We all have good intentions, but real life rarely resembles the smooth aging curve that results from graphing the average data from large groups of people. Instead, there are plateaus and gentle declines punctuated by steep drops—you break a leg, your first kid is born, you become addicted to social media, and so on. Avoiding periods of rapid decline goes a long way toward slowing the overall slide.
Another superstar case study, this one published in 2022 by a team led by Bas Van Hooren of Maastricht University in the Netherlands, illustrates the benefits of consistency. A 75-year-old middle-distance runner named Hans Smeets, who holds multiple European and world age-group records, had clocked a VO2 max of 50.5, equal to the highest known measurement for his age. Smeets only began running at 50, further evidence that it’s never too late to start (or start again). And once he’d begun, he kept going. Over the next 25 years, he never missed more than a week of training. Initially, he ran more than 85 miles per week, and at 75 he was still logging as many as 50. He attributed his ability to handle all that mileage without injury to doing most of his runs at, in his words, “an easy pace.”
That, as it turns out, aligns perfectly with Couzens’s view about what’s required for long-term athletic success: lots of low-intensity exercise. To be sure, the idea of adding an hour of training per month every year to ward off the effects of aging sounds suspiciously like an endurance version of the legend of Milo of Croton, the ancient Olympian wrestler said to have lifted a calf over his head every day until it was a full-grown bull. In both cases, each step in the process seems simple, but the result is nonetheless… improbable, let’s call it.
Yet, as an aspiration, or simply as a formulation of what’s possible, the Couzens Immortality Quotient tells us the same thing as the examples of Tommy Hughes and Hans Smeets, and as Johannes Burtscher’s meta-analysis. You don’t train less because you’re getting old; you get old, to a surprising extent, because skipping that long Sunday run with your pals becomes a habit instead of a rare exception. Don’t do it.
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This article originally appeared on Outside Online.