THURSDAY, April 11, 2002 (HealthDayNews) -- Exercise in a bottle may be a little closer, thanks to new research that has found a way to boost energy production in muscle cells.
The work involves a gene that regulates the activity of mitochondria, the power plants that help cells convert chemicals into mechanical energy. Researchers at the University of Texas Southwestern Medical Center, and Duke University conducted the study, which appears in the April 12 issue of Science.
Muscle-building pills are a couch potato's fantasy, but they do have a higher purpose, at least in theory: aiding people weakened by heart failure, kidney disease and other conditions that make exercise difficult or impossible.
The findings hinge on a family of proteins called calmodulin-dependent protein kinases (CaMK). These molecules play an important role in a wide range of body functions, from muscle contraction to memory. And, as the new study shows, they appear to be a key regulator of the biochemical impact of exercise.
Hai Wu, a research fellow at UT Southwestern, and his colleagues created a strain of genetically engineered mice with a form of CaMK that's always switched on. The result was rodents whose skeletal muscle fibers look as if they've been running marathons compared to their genetically normal cage mates.
The mutant mice had a much higher density of mitochondria in their muscle fibers, Wu said -- just like people who exercise regularly. They also had about five times as much high endurance, "slow-twitch" muscle in their legs as the unaltered animals, whose legs are almost entirely "fast-twitch" fibers that handle short bursts of load. "Those mice have a much better fatigability [susceptibility to getting tired] index.This muscle performed much, much better," Wu said.
The researchers also found that CaMK triggers a gene that codes for another protein, called PGC-1. This molecule in turn shepherds the action of hundreds of others genes that regulate how many mitochondria are in cells, and thus their energy production.
Wu's group is now hoping to translate the results into therapies for people who are unable to exercise because of medical conditions such as heart failure. Ideally, he said, they will be able to selectively interfere with CaMK in muscle to raise the density of slow-twitch fibers. Although big changes in the ratio of fast-to-slow twitch fibers are hard for humans to achieve, small differences are important. "A 10-to-20 percent difference is a tremendous effect," he said.
The work may also help people with diabetes by boosting their supply of slow-twitch muscle fibers, which are more sensitive to insulin than fast-twitch muscle.
What To Do
One fitness expert cautions that Americans are too eager to skirt the hard work of exercise, and could miss out on its many rewards.
"There are qualities that exercise provides that are above and beyond the biochemistry," said Paul Ribisl, chairman of the department of health and exercise science at Wake Forest University in Winston-Salem, N.C. Aerobic workouts strengthen the heart, while weight-bearing exercises like walking and running protect the skeleton. Exercise also has psychological benefits, too, providing a break from daily drudgery and a chance to socialize with others.
To learn more about muscle fibers, try About.com or the University of California at San Diego.
