Leaky Muscle Cells Lead To Fatigue

ScienceDaily (Feb. 12, 2008) — What do marathoners and heart failure patients have in common? More than you think according to new findings by physiologists at Columbia University Medical Center.

The new study shows that the fatigue that marathoners and other extreme athletes feel at the end of a race is caused by a tiny leak inside their muscles that probably also saps the energy from patients with heart failure.

The leak -- which allows calcium to continuously leak inside muscle cells -- weakens the force produced by the muscle and also turns on a protein-digesting enzyme that damages the muscle fibers. The new study found the leak was present in the muscle of mice after an intense three-week daily swimming regimen and in human athletes after three days of daily intense cycling. The same leak was previously discovered by Marks and colleagues in the muscles of animals with heart failure.

The new study also found that an experimental drug developed by the researchers alleviated muscle fatigue in mice after exercise, suggesting that the drug also may provide relief from the severe exhaustion that prevents patients with chronic heart failure from getting out of bed or fixing dinner.

"The study does not mean exercise is bad for you," says the study's senior author, Andrew Marks, M.D., chair of the Department of Physiology and Cellular Biophysics, and director of the Clyde and Helen Wu Center for Molecular Cardiology at Columbia University Medical Center. "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." He notes that athletes' muscles also will return to normal after several days of rest and any muscle damage will be repaired after several days or weeks depending on the degree of exercise.