What do marathoners and heart-failure patients have in common?
Apparently, leaky muscles. Researchers report in the online edition of the Proceedings of the National Academy of Sciences USA that the fatigue extreme athletes feel after a race and that heart-failure patients routinely experience is probably caused by the same condition: a tiny leak that allows calcium to continuously drip inside their muscle cells. According to senior study author Andrew Marks and colleagues at Columbia University Medical Center, the leak weakens the force produced by the muscle and also releases a protein-digesting enzyme that damages the muscle fibers, reducing the ability of a single muscle to contract repeatedly before losing strength. Scientists discovered the leaky muscles in mice put through a grueling three-week swimming regimen and in humans after three days of intense cycling. The findings mimicked earlier ones they found in animals with heart trouble. But don't think this gives you an excuse to be a lazy bum.

"The study does not mean exercise is bad for you," Marks stressed. "We only saw the leak in animals and human athletes that exercised three hours a day at very high intensities for several days or weeks in a row until they were exhausted." What's more, he noted, the athletes' muscles returned to normal after a few days of R&R. People with chronic heart failure, on the other hand, had the problem even though they didn't do a lick of exercise; and unfortunately, their damaged arm, leg and breathing muscles didn't bounce back. But researchers also found that an experimental drug they had developed relieved muscle fatigue in mice after exercise, suggesting that it may also perk up patients with chronic heart failure who are sometimes too weary to even get out of bed. (Columbia University Medical Center)

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