In a paper that will appear in the August 24 issue of the online journal PLoS Biology, the scientists say the inability of these genetically modified mice to generate energy through anaerobic metabolism, the biochemical process used for short sprints or bursts of power, provides them instead with an extraordinary capacity for longer, sustained aerobic endurance exercise.
But while these endurance-enhanced mice can run and swim to exhaustion in laboratory tests for far longer periods than their normal counterparts, the scientists discovered that their super-endurance capabilities appear to be only temporary and come at a high price. After four days of exercise tests, the gene-doped endurance mice exhibited significantly more muscle damage and were unable to run or swim as long as their normal counterparts.
"It's a double-edged sword," says Randall S. Johnson, a professor of biology at UCSD, who headed the study. "By changing the way skeletal muscles respond to low-oxygen levels, we've developed muscles that appear to be superiorly adapted or trained for long bouts of submaximal aerobic exercise. But these muscles also become damaged more easily than normal muscles during exercise and we don't know why."
The discovery not only has obvious importance for physiologists and others who study muscle metabolism to maximize human endurance. It should be of keen interest to medical researchers seeking treatments for human genetic disorders, such as McArdle's disease, whose sufferers tire quickly during exercise because they have an impaired ability to generate energy through anaerobic metabolism and experience soreness and pain after exercising because
Contact: Kim McDonald
University of California - San Diego