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).
Recommendations
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.
References
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.
