Exercise: the more the better?

Dov Michaeli

First published 4/21/11 on The Doctor Weighs In.

This thought occurred to me when I read that Grete Waitz died a few days ago of cancer at age 57.

Grete was a Norwegian schoolteacher, a superb runner, and a wonderful human being. She twice set the world record at 3,000 meters, and she set world records at distances of 8 kilometers, 10 kilometers, 15 kilometers and 10 miles. But her most famous accomplishments were in the marathon race. She won 9 New York marathons –a record for either men or women. In addition to her New York City victories, Waitz won the London Marathon twice, the Stockholm Marathon once and the world championship marathon in 1983.

She put marathon running on the map. More than 35 new marathons launched in 2010 – a record number bringing the total to more than 625 U.S. marathons last year. That’s up from about 200 in 1985. And the number of runners crossing the finish line annually in U.S. marathons passed the half-million mark in 2010, at 507,000. Perhaps more important, she blazed the trail for women running. Just 938 out of 8,937 entrants in the 1978 New York marathon were women (about 10.5%) — in 2010, 16,253 of 45,350 entrants were (36%).

Not all runners are created equal

As an avid marathon runner myself I admired those super runners in perfect physical shape. The story of Dan Karnazes, a real life Forrest Gump, was an inspiration. Between 1992 and 2006 Karnazes challenged almost every known endurance running limit. He covered 350 miles without sleeping. (It took more than three days.) He ran the first and only marathon to the South Pole (finishing second), and in 2006, at age 44, he completed 50 marathons in 50 consecutive days, one in each of the 50 states. (The last one was in New York City. After that, he decided to run home to San Francisco.) Crazy, I thought, with a tinge of envy.

But is it good for you?

An interesting study was done in Liverpool, England. They studied the ECG and troponin I (a blood test for cardiac damage) of elite runners participating in a grueling race of 50 or 100 miles. Professor Somauroo summarized the results, “This study suggests that running continuously over 50 or 100 miles may not be good for the heart. 96 percent of the finishers developed a significant increase in cardiac Troponin I, which can be an indicator of heart muscle damage — and 12 percent showed signs suggestive of significant cardiac damage. They also developed significant electrical changes on their ECGs and, in some cases, quite bizarre changes”

Another study showed that a low key, definitely un-macho daily walk for 30 minutes yields 90% of the metabolic benefits (weight control, avoidance of diabetes) as well as the cardiac benefits of exercise; running adds an extra 10%.

For those of you who don’t like to run –walk. Ninety percent of benefits ain’t so shabby. For those who want the extra 10%-go out and run, swim or lift weights. But do everything in moderation. The price that ultra runners pay in cardiac pathology is simply not worth it.

Dov Michaeli MD, PhD is a basic researcher writing on The Doctor Weighs In.

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