Getting at least some moderate exercise is good for us, and more is
even better, doctors and public health experts say. But is there such a
thing as
too much exercise?
Apparently, yes, according to researchers led by Dr. James O’Keefe, a
cardiologist at the Mid America Heart Institute of St. Luke’s Hospital
in Kansas City, Mo. Reporting in the journal
Mayo Clinic Proceedings, O’Keefe and his colleagues found that physical activity, like any medical treatment, can be harmful if it’s overdone.
“As great as exercise is, it’s like a powerful drug,” he says. “More
is better up to a certain dose, but after that there is a point of
diminishing returns, and it may actually detract from [heart] health and
even your longevity.”
(
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O’Keefe reviewed studies of people who trained and participated in
marathons, triathalons, ultramarathons or long bike races — people who
exercised at extreme levels. Overall, people who exercised regularly
reaped significant benefits, tending to live seven years longer than
those who are physically inactive. But when O’Keefe focused only on the
extreme athletes themselves, he found that the healthy effect of all
their activity tended not only to wane, but to actually reverse itself
and turn toxic.
Studies showed that during and immediately following a
marathon, runners showed up to a 50% increase in levels of an enzyme called
troponin,
which signals damage to the heart (it’s the same enzyme that shoots up
in patients having heart attacks). Troponin is released when heart
muscle is in distress, and in the case of lengthy extreme exercise
sessions, it may start to climb as heart muscle fibers start to tear
under the intense burden of pumping continuously at a high level.
“When you’re sitting around, you heart is pumping about five quarts
of blood a minute, and if you run up the stairs or hard or push yourself
physically, it can go up 35 or 40 quarts a minute,” says O’Keefe. “If
you go and run for 26 miles, or do a full-distance
triathalon,
it completely overtaxes the heart. The heart is pumping 25 quarts a
minute for hours and hours, and that starts to cause muscle fibers to
tear, which leads to a bump in troponin and other enzymes associated
with inflammation, and it causes the death of some muscle cells in the
heart.”
(
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Over time, that damage can cause scar tissue on the heart, and a
thickened and scarred heart is more vulnerable to abnormal heart
rhythms, says O’Keefe. Indeed, people who chronically exercise at
extreme levels tend to have thicker right atria (which receive
deoxygenated blood from the veins) and larger right ventricles (which
pump this blood out to the lungs to be oxygenated and circulated).
Studies show that endurance athletes have a five times higher risk of
atrial fibrillation, or fluctuations in the heartbeat that can trigger more serious heart problems.
In the new data, presented at the annual meeting of the American
College of Sports Medicine, one of the study co-authors, Dr. Carl Lavie,
medical director of cardiac rehabilitation and prevention at the John
Ochsner Heart and Vascular Institute in New Orleans, reported on the
optimal “dose” of running for increasing life expectancy. Among 14,000
runners, the optimal amount of exercise appeared to be about 10 to 15
miles per week. “We were thinking that we would see progressively more
benefit the more you ran,” says Lavie. “We thought it would level off at
some point. But not only did the runners not get more benefit, but the
more they did, the faster they ran, the more frequently they ran, the
more miles they ran, they actually seemed to lose any benefit to the
heart.”
No matter how much they ran, however, they didn’t do worse than
non-runners when it came to longevity, Lavie says. But there was a limit
to how much exercise contributed to life span. Beyond that point, he
says, physical activity started to have a negative, or harmful effect
and cut away at any improvement the runners may have accumulated to that
point.
(
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The damage doesn’t happen overnight; rather, it builds up over years
of training. That’s why O’Keefe, an avid exerciser himself, doesn’t
discourage patients who are interested in participating in marathons
from trying them. But he counsels hopeful marathoners to consider their
race experience a once-in-a-lifetime thing. “If they want to train for a
marathon, to cross it off their bucket list, I tell them okay, but it’s
not a healthy long term habit to get into,” he says.
Given the results from O’Keefe’s analysis, it makes more sense to
exercise at moderate levels. “We have people who are more and more on
the extremes. Over the last 35 years, obesity rates have tripled in
America, and the number of people completing marathons has gone up
20-fold,” he says. “What we need are more people doing moderate exercise
daily, and not running heroic distances. You can get 70% to 80% of the
benefit of exercise from doing it 15 to 30 minutes a day.”
And that’s the real lesson from the study. It’s not that exercise is
bad for the heart or that it’s better to sit on the couch than go for a
run — it’s that the heart and longevity benefits of exercise don’t
require extreme efforts. When it comes to exercise, a Goldilocks
approach is probably best: too little isn’t good for heart, but neither
is too much. Moderate physical activity — anywhere from 15 minutes to an
hour a day, several days a week — is just right.
VIDEO: Walking While Working
Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.
Read more: http://healthland.time.com/2012/06/04/extreme-workouts-when-exercise-does-more-harm-than-good/#ixzz2AIz95ZhF