How Much Exercise Is Too Much?

There is an interesting Ted talk on this topic entitled Run for your life! At a comfortable pace, and not too far by Cardiologist James O’Keefe. He argues that more vigorous exercise like running (and other aerobic exercise of similar intensity) has an inverted U-shaped curve of health benefit. Doing some exercise confers significant health benefits compared to none, but the benefits go down with too much exercise. In contrast, for lower intensity exercise like walking, more is needed to confer the benefit, but it seems like you can pretty much “do it all day”, as Dr. O’Keefe puts it, without the benefits going back down. Some evidence for this is from a study from Taiwan (Ref. 1) which shows sharp reduction in all-cause mortality for vigorous exercise up to 50 minutes a day, after which it plateaus. For moderate exercise, the benefits continue until at least 110 minutes per day. However, the reduction in all-cause mortality is less. This suggests to me the optimum might be a combination of a smaller amount of vigorous activity and a larger amount of moderate activity. Here is the figure from the study:

The daily activity is an average, so, for example, if you exercised vigorously for 60 minutes 4 days a week, you’d average 34 minutes a day.

The authors of ref. 1 defined moderate activity as about 4.5 METS (Metabolic equivalents; 1 MET is sitting), while vigorous is 8.5. I cross-referenced that with a physical activity chart. Walking, including brisk walking, is moderate, as is leisurely biking (10 km/hr or 6 mph). Many activities of daily living like housework or gardening fall in the light to moderate category. It only takes jogging at 9 km/hr (5.5 mph) to reach 8.5 METS, or brisk bicycling on the flat (25 km/hr or 15,5 mph), There’s a complete list in ref 2.

Note that the data from ref. 1 (figure above) show a leveling off of benefit with increased amount of exercise but don’t show a decrease with further exercise (an inverted U-shaped curve). But Dr. O’Keefe gives evidence of the U-shaped effect in Ref. 3.

In the Ted talk Dr. O’keefe goes on to describe how excess vigorous activity over time has adverse effects on the heart like scarring and ventricular wall thickening, and on the coronary arteries like excess calcified coronary plaque, and cites evidence from Ref. 3. He mentions the scary fact that if you test runners at the finish line of a marathon, a large percentage of them will have troponin in their blood, an indicator of heart muscle damage. This is due to microtearing, which will heal from one marathon (or 3 in a lifetime, like yours truly). But put your heart through this multiple times for years and the damage will accumulate, as was found in a study of marathoners who had completed more than 25 over many years. One of the issues this damage can lead to is afib, which I’ve discussed previously.

I don’t think there’s enough data to suggest how much vigorous exercise is too much. But the Copenhagen City Heart Study (ref. 4) suggests health benefits are lost when running at a brisk pace for more than 2.5 hours per week, while the optimum dose appears to be slow to average paced jogging at about 2.5 hours per week. The accuracy of this exact number might be debatable, but the idea that too much of a good thing is possible for vigorous exercise is the takeaway message.

All of this is assuming a single pace. It is often suggested it’s better to alternate easy and hard days, as well as “polarizing ” training by mixing a lower volume of higher intensity activity with higher volume of lower intensity activity. So something like up to 2 hours of vigorous activity, perhaps split into 2 or 3 hard days, interleaved with several hours of moderate activity on the other days, could well be ideal. That’s pretty much what I do. I do shorter sessions of high intensity exercise like strength training or biking intervals about 3 days a week, and longer amounts of more leisurely cycling or brisk walking on the other days.

I actually saw the Ted talk that prompted this post a while back. What motivated me to write about this now was an interesting discussion in the book Too Old to Ultra by Stephen Morley that I just read (it is in the chapter “Are Ultras Bad for Your Health”) . Stephen is is my age (66) and still runs ultramarathons. He survived a heart attach suffered while hammering hard up a hill at the age of 57 in a 7 mile road race, described in detail in his previous book Running With a Wounded Heart. These are both interesting and inspiring reads. In the discussion in “Are Ultras Bad for Your Health” he argues that ultramarathoning may actually be safer than marathoning, at least among non-elite runners, because you actually spend a lot of your time at a slower running pace or walking, interspersed with bursts of more vigorous running or power-hiking up steep hills. By contrast, marathon runners, even non-elites, are often pushing the pace more of the time. He may be right, at least in his own case. But Stephen also admitted 74% of ultrarunners interviewed said they would continue doing ultramarathons even if they were convinced it was not good for their health. I sympathize with that sentiment. The good feelings we can get from our physical activities can be hard to resist. But I think with a proper combination of pace and volume as discussed above, you can get the good feelings and improved health.

And I must close by emphasizing that the vast majority of people get too little or no exercise, not too much. The authors of Ref. 1 show the profound health benefits of as little as 15 minutes a day of vigorous exercise compared to being sedentary, and the recommend amount is at least 30 minutes a day on most days.

References

1. Pang-Wen, C, Pui Man Wei, J, et al, “Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study”, The Lancet, 2011. Available online at https://www.welhatsports.org.uk/uploaded/files/lancet.pdf
2. Jette, M, Sidney, K and Blumchen, G, “Metabolic Equivalents (METS) in Exercise Testing, Exercise Prescription, and Evaluation of Functional Capacity”, Clin. Cardiol., 1990., available online at https://onlinelibrary.wiley.com/doi/pdf/10.1002/clc.4960130809
3. O’Keefe, J, et al, “Potential Adverse Cardiovascular Effects From Excessive Endurance Exercise”, Mayo Clinic Proceedings, 2012., available online at https://www.sciencedirect.com/science/article/abs/pii/S0025619612004739
4. 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