Researchers at the Columbia University Medical Center have found a similarity between marathoners and heart failure patients - leaky muscle cells.
According to the study, 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 study, conducted by 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 and colleagues, found that 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.
Marks and colleagues have found the same leak previously in the muscles of animals with heart failure.
"The study does not mean exercise is bad for you. 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," Marks said.
He also noted that athletes' muscles 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.
On the hand, the arm, leg and breathing muscles of patients with heart failure never have a chance to recover.
"People with chronic heart failure are subject to this same kind of muscle leak and damage constantly even without doing any exercise," Marks said.
His previous study in muscles of mice with heart failure suggested that fatigue in patients stems from the calcium leak, which reduced the ability of a single muscle to contract repeatedly before losing force.
"We then had a hunch that the process that produces fatigue in heart failure patients also may be responsible for the fatigue felt by athletes after a marathon or extreme training," said the study's first author, Andrew Bellinger, Ph.D., who is currently finishing his M.D. at Columbia University's College of Physicians & Surgeons..
The current 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 results will be published in the online edition of the Proceedings of the National Academy of Sciences.