Physiology Friday #235: What We Can Learn About Exercise and Aging From an Outlier of Human Physiology
Do the pros of extreme endurance exercise outweigh the potential downsides?
Greetings!
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Now and then a study catches my eye that strays from the randomized controlled trials that I usually cover in my newsletter. That’s the case this week, but trust me, I found this one too cool to pass up, and I know you’ll love reading about it.
This study is " atypical " because it’s a case study — an n=1 characterization of an extreme outlier of physiology, performance, and healthy aging. Trust me, you’ll learn more about healthy aging from this case study than you will from any longevity guru.
How much exercise is too much exercise? While this hasn’t been firmly established, we have data that endurance athletes who perform high levels of exercise (10–15 or more hours per week for 20+ years) have more heart arrhythmias and evidence of coronary artery calcification compared to less-active people. Does this mean that endurance exercise is harmful to the heart despite several of its other well-known benefits?
It’s a hard problem to study, mostly because these data come from cross-sectional studies comparing “extreme exercisers” to recreationally active people at a single point in time.
If a 60-year-old marathon runner has a few things wrong with his heart, this tells us nothing about what his heart looked like at age 20 or how it changed during those 40 years. Nor can we conclude that the changes to his heart occurred directly as a result of his endurance exercise training, genetic and lifestyle risk factors, or a combination of these variables.
However, it’s clear that the hearts of endurance athletes are much different than those of non-athletes.
Lifelong athletes also have more beneficial risk factors, for example, a higher VO2 max compared to the general population. This undoubtedly provides a longevity advantage since aerobic fitness is one of the strongest predictors of morbidity and mortality.
Again, it’s hard to directly say whether this aerobic fitness in middle and old age was obtained via a genetic gift, a lifelong building of fitness through hard work, or a preservation of fitness over time.
We can only learn these answers if we have longitudinal assessments of someone’s physiology — several measures taken at multiple time points throughout life to note the trajectory of things.
Lucky for us, this case study provides just that, and it enables some unprecedented insight into the physiology of aging in an extreme endurance athlete.
This case study, published in the Journal of Applied Physiology, profiles 77-year-old former world-record holder “DC” (initials are used to protect his identity, although we can be sure this individual is Derek Clayton, a former elite marathon runner).1
In 1967, DC became the first man ever to break 2:10 in the marathon, routinely logged 150–300-mile training weeks, and continues to engage in between 10–15 hours of endurance exercise (running and cycling) each week at the age of 77.
In other words, this is someone who has been engaging in extreme endurance exercise for his entire life. If there’s anyone at risk for the perils of “extreme exercise” or from whom we can learn something about the risks and benefits of lifelong endurance training, it’s DC. He’s our model organism and the epitome of extreme exercise.
Luckily, we’ve got 50 years of data on DC, including VO2 max tests from when he was 27, 49, and 77 (present-day) and cardiac function assessments at age 77.
Remarkably, his VO2 max barely changed from age 27 (69 ml/kg/min) to age 49 (68 ml/kg/min) even in the context of a 12 beats per minute reduction in his maximal heart rate (188 at age 27 vs. 176 at age 49).
At age 77, he had a VO2 max of 43.6 ml/kg/min — a value that’s nearly 240% higher than his age-predicted fitness level. From age 49 to age 77, his VO2 max dropped by 1.3% per year (this is in line with the ~10% decline per decade reported in the literature). During the same time frame, his maximal heart rate dropped by 22 beats per minute (an expected finding given that our maximal heart rate falls about 1 beat per minute per year).
Let’s put his aerobic fitness into context. The average VO2 max for someone 70–79 is 21 ml/kg/min, less than half of DC’s value! The disability threshold for functional independence — a fitness level where activities of daily living become difficult to complete — is 18 ml/kg/min. DC’s “functional reserve”, the difference between his value and the disability threshold, is nearly 26 ml/kg/min. He won’t reach the functional disability threshold until he’s about well past 100 years old (given his current rate of decline). Talk about protection against aging.
A thorough examination of cardiac structure and function revealed some remarkable and some unremarkable (in a good way) findings, which included diastolic volumes above the 95th percentile for his age. The remodeling of his heart — including a larger left ventricle mass and chamber size — was indicative of the eccentric cardiac remodeling characteristic of endurance athletes. He also had a resting heart rate of 38.
What’s fascinating about these findings is not only that DC’s values were (not surprisingly) well above those for his age- and sex-matched peers, but most of them were above those reported in well-trained endurance athletes.
Notably, other assessments found no evidence of scarring or inflammation of the heart.
DC was also compared to two younger participants during exercise: one endurance-trained 23-year-old and another untrained 23-year-old.
During exercise, DC was able to increase his stroke volume (the amount of blood ejected from the heart each beat) similar to a well-trained 23-year-old athlete and more than a 23-year-old untrained control participant. He could generate a large stroke volume that allowed him to achieve a high cardiac output during cycling exercise even when his heart rate only reached 111 beats per minute.
His cardiac output during maximal exercise was comparable to that of the well-trained endurance athlete and the healthy control participants who were more than 50 years younger.
Despite (or perhaps due to) his extreme physiology, Derek also presented with complications that were noted in the case study. This included atrial fibrillation (a heart arrhythmia) and fatigue that occurred shortly after he completed his lab assessments, necessitating extensive cardiac procedures to return him to a normal rhythm, and highlighting the potential costs of extreme exercise.
The first thing that stood out to me about this study is that despite maintaining an insane level of commitment to endurance exercise, DC still displayed the same age-related declines in VO2 max observed in recreationally active adults.
He didn’t “prevent aging” by slowing the aging process, but by starting with a (much) higher aerobic fitness reserve from which to draw. This is a finding we should all take heed of. Nobody is immune to aging, but the healthier we are in early and mid-life, the better off we’ll be in late life. No matter your age, you need to work on building a reserve of aerobic fitness (and muscle mass and strength). And the best time to start was yesterday.
This also points to the fact that if we want to maintain an extraordinary level of fitness into old age, then we have to engage in extraordinary levels of exercise. Maybe not Derek Clayton levels…but as close as we can get.
The clear limitation here is that there is a genetic component to endurance performance and VO2 max. There’s no doubt that DC started life with a higher fitness level than most mortals will ever achieve in their primetime of life. But there’s also no doubt he worked hard to maintain it.
The second thing is the glaring reality that a lifetime of extreme endurance exercise — at least in the example here — did have some cardiac consequences.
Despite some adverse cardiac remodeling (most of which is well documented among athletes), DC was able to maintain elite levels of athletic performance, not just for his age, but for people more than half his age. On most occasions, his heart did not limit his day-to-day functional capacity.
Perhaps then there is a trade-off to make when it comes to aging. After all, DC’s body composition, muscle mass, and other health metrics were superb for a 77-year-old. One could argue that his cardiac side effects — not to be dismissed — are usurped by the other benefits achieved through intense exercise that exert a protective effect against aging.
Indeed, atrial fibrillation is a well-accepted consequence of endurance training — the risk is 5-fold higher in athletes — due to enlargement of the two heart chambers known as the atria. But many (including myself) continue to participate in “extreme” levels of exercise even when knowing this potential downside (and in my case, sometimes experiencing it directly).
Maybe it’s not so hard to justify this added risk. Even though atrial fibrillation is higher in athletes, the risk of dying from atrial fibrillation, stroke, or any other cardiovascular disease is much lower than in the general population (those with and without atrial fibrillation).
That goes back to tradeoffs. Doing a lot of exercise may be risky, especially for people with additional risk factors or a family history. And of course, not doing any exercise is perhaps the riskiest business of all. Like all things, the “optimal” amount of exercise to promote healthspan and longevity probably lies somewhere between the two extremes.
But if you’re anything like me and enjoy endurance exercise (or resistance training or any other type of exercise), pushing to the extremes is a way to find joy. And if, like the case study covered here, we can be “extreme” about our dedication to health habits, perhaps we can be outliers when we get to a very, very old age.
I’m counting on it.
Thanks for reading. See you next Friday.
~Brady~
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Great post! Thanks! As a cardiologist and endurance athlete, I share these concerns about a fib. I'm sure I'll get it eventually. As well as some coronary calcifications. But the trade offs are worth it. If nothing else for the neuro and mental health benefits.
Just about as impressive is staying healthy enough to train that much over that length of time.