Tuesday, May 12, 2015

Feature Article: Can you exercise too much?

There has been a major push in the last few years towards extreme fitness. The trend right now is to exercise to the absolute limit of your abilities. People are flocking to boot camps and intense interval cardio classes. Every year, more people run marathons and take part in other extreme endurance events like bike races and “survival” obstacle course races. 

I am generally a big fan of fitness fads. Anything that gets people excited to work out is cool with me. However, this really high intensity training trend has always made me a bit nervous. I learned about overtraining when I was getting my Masters in Exercise Science. The American College of Sports Medicine has published a comment on overtraining, citing that excessive exercise can cause a variety of symptoms, including fatigue, depression, sensitivity to stress and impaired immune system function (Reference 1). 

The prevailing wisdom was that overtraining was not such a big deal and these symptoms were generally self-limiting and benign. Recently however, a new area of research suggests that this may not be the case. I read a newly published article in the Journal of the American College of Cardiology that was eye opening and prompted me to dig deeper into this question.

The Study
In this investigation of the Copenhagen City Heart Study cohort, 1,098 healthy joggers and 3,950 healthy non-joggers were followed for 10 years (Reference 2). The exercise habits of the runners were measured and the impact of these habits on long term risk of death were examined. The results were shocking.

Based on the reported intensity, frequency, and duration of training, runners were broken up into 3 categories; light joggers, moderate joggers, and strenuous joggers. The light joggers had a statistically significant 78% lower risk of dying when compared to sedentary subjects. The moderate joggers had a nonsignificant 34% lower risk of dying, while the strenuous joggers had a nonsignificant 197% increased risk of dying.

Subjects that ran the hardest and longest had no benefit to longevity when compared to those that didn’t exercise at all! 

Why Didn’t The Strenuous Exercisers Live Longer?
This is the million dollar question. The authors of the study offered several possibilities with plenty of references. Most of the proposed mechanisms dealt with damage to the heart. I picked up the relevant articles and looked at them in detail. Here is what I found as far as potential problems with very intense exercise:

1) Pathological restructuring of the heart and large arteries (Reference 3).

2) Elevations in troponin after intense exercise, which is a highly specific marker of myocardial cell damage (Reference 4).

3) Premature aging of the heart (Reference 5).

4) Increased risk of myocardial fibrosis, which increases risk of arrhythmia (Reference 3).

5) Increased coronary artery calcification (Reference 3).

6) Large artery wall stiffening (Reference 3).

7) Increased oxidative stress (Reference 3).

8) Renal dysfunction (Reference 3).

9) Increased risk of atrial fibrillation (Reference 3).

10) Immune system dysfunction (Reference 3).

The research here is in a relatively early stage and there is clearly more work to be done. However, after going through these studies in detail, I think there is something to the idea that very long and/or very intense exercise may be more harmful than beneficial to health and longevity.

This in no way lessens the astronomically positive impact of physical activity on health. Even in this study, those considered “light joggers” had a stunning 78% lower risk of dying during the follow up period. It’s just that as intensity goes up, health benefits may go down. 

As far as recommendations, here is what I tell my clients:
1) Limit total exercise to 45-60 minutes per day max and don’t go crazy with the intensity. Think of a time when you were late to an appointment and you were walking as fast as possible to get there without running. That is the level of cardio intensity I have my clients shoot for. If you are young, healthy and in good shape, a few intervals of increased speed for 30 seconds thrown in are probably OK.

2) Avoid marathons, long bike races, and “survival” races. They are not necessary for weight loss/health promotion and may be damaging to your health.

3) As far as weight training, keep the intensity moderate. Most of the studies I looked at were about cardiovascular exercise, but there is some evidence that any really intense exercise, even if it is of short duration, may cause issues. I always tell my clients that when they finish their cardio or weight training, they should feel like they could do a bit more.

It may just be that when it comes to exercise, the goals of health promotion and longevity may differ radically from the goals of maximizing strength, speed, and physical performance. It also may be that a program designed to reach one of those goals excludes you from reaching the other.

1) https://www.acsm.org/search-results?q=overtraining

2) Schnor P, et al. Dose of jogging and long term mortality. Journal of the American College of Cardiology 2015; 65:411-19.

3) O’Keefe JH, et al. Potential adverse cardiovascular effects from excessive endurance exercise. Mayo Clinic Proceedings 2012; 87:587-95.

4) Shave R, et al. Exercise-induced cardiac troponin elevation. Journal of the American College of Cardiology 2010; 56:169-76.

5) O’Keefe JH, et al. Exercise for health and longevity vs peak performance: Different regimens for different goals. Mayo Clinic Proceedings 2014; 89:1171-75.


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