How Much Exercise Is Too Much? – Revisited

Recently I discussed the notion that there can be too much of a good thing with exercise. Some doctors believe there is a U-shaped curve of exercise and health. Health benefits increase, and risk of mortality from all causes decreases, as amount of exercise increases- up to a point. With too much exercise the benefits can go back down and the risks of side effects like AFIB go up.

An important 2018 study [1] from the Cleveland Clinic, a world-renowned cardiology center, at least partially calls this into question. A found out about this in a post on my fellow blogger Tony’s site, and he also has some interesting comments there.

The Cleveland Clinic researchers came at this from a different angle. Previously, for example in the Copenhagen Study [2], researchers have looked at mortality and disease risk vs. volume of exercise, often self-reported in questionnaires. Instead, in the Cleveland Clinic study, cardio fitness was directly measured and correlated with long-term mortality. The results were readily available because the clinic routinely performs exercise stress testing on patients. From these fitness levels can be precisely determined. With results of over 122,000 patients over the years, good statistics could be accumulated on fitness vs. all-cause mortality. Brilliant! I don’t know why this has not been thought of before. Cardiologists all over the world run these tests, and I have undergone one myself. I’ll describe that below.

But first, the bottom line: no U-shaped curve was found. No upper limit. The fitter you are, the less long-term risk of mortality from any cause. Period. Those with “high” level fitness had much lower risk than those with low. But those with “elite” level fitness had even less.

An exercise stress test is a test, usually on a treadmill but sometimes on an exercise bike, where you start out slowly and every couple of minutes the intensity goes up. You’re hooked up to an ekg so your heart rate is monitored and arrhythmias can be detected. Both fitness levels and intensity can be precisely measured in this test. In my case, a little over 2 years ago (shortly after I’d been diagnosed with aortic stenosis), it was a treadmill test. I started out walking, leisurely, on a flat surface. Piece of cake. Then a couple minutes later I heard a beep and it got faster, but still not bad. Then another beep and the treadmill threw in some incline and got faster. This kept happening, relentlessly. Eventually I was running hard up a 10% incline. Definitely not a piece of cake. All this time my heart rate was being recorded along with speed and incline. The tech shut it down when my heart rate reached 171. I actually felt like I could have gone a bit harder although the barf threshold was not far away. I felt like I had passed the test with flying colors. I later found out that some arrhythmias had showed up on my ekg which is why the test was stopped. This was an early indicator of my afib, a side effect of my aortic stenosis (which is thankfully gone now).

How to Explain the Difference With previous studies?

Volume of exercise does not correlate directly with fitness. Even if you measure something like MET-minutes per week of activity, which captures a combination of intensity and volume, it is not the same as fitness. That is because there are optimum ways to train to achieve fitness, like the old maxim “work harder not smarter”. I’ve discussed previously techniques like polarized training and interval training that are thought to achieve good fitness benefits with minimal health risks. In contrast, many people who become enthused about recreational activities do a lot of volume at a moderately high intensity level, which is actually not the best for fitness or health. A lot of coaches call it “no-man’s land”. A person with a lower volume of training, but with higher intensity thrown in, can actually be fitter. Previous studies, that just measure volume of exercise or even “Met-minutes”, will include lots of people training inefficiently at high volume. The Cleveland Clinic focussed on the bottom line, fitness.

Based on the Cleveland Clinic results, I think a case can be made that some experts have overreacted to the “U-shaped” evidence. For example, cardiologist Dr. James O’keefe entitled his youtube talk on this subject “Run for your life! At a comfortable pace, and not too far“. Maybe it should have been “at a comfortable pace most of the time, with some high intensity thrown in once in a while”.

I personally train more than 90 minutes a day on average. Probably 90% of that is walking or leisurely hiking or biking. About 10% of the time I work out hard, at strength training or brisk hiking or biking, typically done with intervals. That much volume is unnecessary, but I find the leisurely stuff pleasurable and relaxing. My favorite fitness role model, Clarence Bass, at 80+ years old, spends a lower amount of time, maybe about 45 minutes a day doing brisk walking. And a couple times a week he goes really hard at strength training and cardio. In his words “I walk and I sprint, I don’t do anything in between”. I’m pretty sure I’d show up as high fitness for my age if the Cleveland clinic tested me, while Clarence would undoubtedly be elite.

The most important thing is to get off the couch!

The emphasis in this post is “the fitter your are the better”. But the most important health improvement occurs in those who were previously sedentary and get moving. The Cleveland Clinic authors published another paper based on the exercise test results which shows that your fitness is more important than your age in predicting risk of dying. I’ll go over that in the next post.

References

1. Mandsager, K, et al, “Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing”, JAMA Network Open, 2018.
2. Schnorr, P, et al, “Dose of Jogging and Long-Term Mortality: The Copenhagen City Heart Study:, Journal of The American College of Cardiology, 2015., available online at https://www.sciencedirect.com/science/article/pii/S0735109714071745