By Katherine Harmon | Scientific American – 22 hrs ago
Image courtesy of iStockphoto/Maridav
If getting some exercise is good for you and getting lots is even better, then hours upon hours of intense exercise must be best, right? Perhaps not.
Many people feel obligated to hit
the gym or the trail every now and then to help keep off the extra
pounds. But people who run ultra marathons (usually 50 kilometers or
more), ride in long-distance bicycle races, compete in or even just
train for consecutive are not usually doing it just to stay trim.
Nevertheless, long-term health benefits (stress injuries aside) of so
much exercise are usually presumed to be a bonus.
A new study, published online June 4 in Mayo Clinic Proceedings,
suggests, however, that this “excessive endurance exercise” might
actually be putting people at risk for permanent heart damage and
“A routine of daily physical activity can be highly effective for prevention and treatment of many diseases, including coronary heart disease, hypertension, heart failure and obesity,” James O’Keefe,
of the Mid-America Heart Institute of Saint Luke’s Hospital of Kansas
City and co-author of the study, said in a prepared statement. But after
reviewing the literature on extreme-endurance event participants, he
and his colleagues found evidence that over time this type of training
might be changing people’s hearts and not for the better.
The researchers found that many of these athletes had temporarily elevated levels of substances that promote inflammation
and cardiac damage. One study found that as many as half of runners in
the midst of, or who have just finished, a marathon show these spikes,
which can last for days after an event. And over time and with repeated
exposure, these compounds can lead to scarring of the heart and its main
arteries as well as to enlarged ventricles all of which can in turn
lead to dangerous irregular heart beats ( ) and possibly sudden cardiac
death.
“Physical exercise, though not a
drug, possesses many traits of a powerful pharmacologic agent,” O’Keefe
said. “As with any pharmacologic agent, a safe upper dose limit
potentially exists, beyond which the adverse effects of physical
exercise, such as musculoskeletal trauma and cardiovascular stress, may
outweigh its benefits.”
Earlier this year ultra runner Micah True, also known as Caballo Blanco, made famous by Christopher McDougall’s book
(Knopf, 2009) for running with the Tarahumara tribes in Mexico, died at
the age of 58 while on a relatively short trail run. The medical report
concluded that he had a scarred, enlarged heart and likely died from
arrhythmia.
But plenty of people who do not
train with the Tarahumara might be at risk. Some 500,000 people finished
at least one marathon in the U.S. in 2010, and some 70,000 people run
ultra marathons around the world each year. Screening for factors to
find people who might be at a particular risk so far is unproven and
would likely be expensive. So the researchers suggest that athletes dial
back intense exercise to about an hour per day (sessions can be longer
if exercise is less rigorous) or at least have regular visits with their
doctors to check up on their heart health.
also highlights potential
downsides of exercise for some people. Claude Bouchard of the Human
Genomics Laboratory at the Pennington Biomedical Research Center in
Baton Rouge Louisiana, and his colleagues report that in many exercise
studies, moderate to intense exercise elevated one or more indicators of
risk for cardiac disease or diabetes in a subset (about 10 percent) of
the population in the analysis. The authors did not follow the subjects
to see if these people were actually more likely to have poor health
outcomes, however. And for the rest of the subjects, most of them saw
improvements in these risk factors.
But the new findings do not
negate the benefits of regular exercise for most people. It adds an
average of seven extra years of life expectancy, and it also increases
the likelihood that people will spend more of those years relatively
trim and in good health. “Exercise is one of the most important things
you need to do on a daily basis,” O’Keefe said. But, he noted, “extreme
exercise is not really conductive to great cardiovascular health. Beyond
30 to 60 minutes per day, you reach a point of diminishing returns.”
Indeed, a long-term study of 52,000 runners found that those who ran
one to 20 miles a week spaced out over two to five days and at an 8.5-
to 10-minute mile lived longest.
Indeed, these days, the best bang
for your buck seems to be a daily short session just 20 minutes or so
of intense, , such as repeated bursts of intense running, biking,
swimming or strength training with short recovery periods in between.
And, hey, that'll also leave you with a heck of lot more free time than a
daily 20-mile training run.
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