Several years ago, NASA asked UAB physiologist Marcas Bamman, Ph.D., to figure out why astronauts lose muscle in the zero-gravity environment of space. Bamman set to work, putting healthy young subjects on bed rest for up to 17 weeks. He found that without the constant strain of moving a body around, muscles began to rapidly waste away, losing 20 percent of their mass within 14 days. Those experiments eventually led Bamman to think about a similar problem: muscle atrophy in aging adults.
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"From ages 30 to 50, there's about a 5 to 10 percent loss of muscle mass," he says. "But from 50 to 80, it's a much steeper decline, about 1 percent per year. So over that 30-year time frame, you could lose 30 percent of your muscle mass." Muscle loss makes it harder to maintain balance, climb stairs, and rise from a seated position. It also plays a role in type-2 diabetes, osteoporosis, and other conditions.
Bamman and his research team are working to slow or even reverse the process. Using traditional weight-training techniques in innovative combinations, they were able to achieve surprising results in a five-year trial funded by the National Institutes of Health. "Aging is a disease of fast-twitch, or type-2, fibers," says Bamman. "And we've been able to restore the size of the type 2s in older adults to the same level as in young people." In other words, after four months of training, 65-year-old subjects can have the muscle fibers of untrained 25-year-olds—but only if they continue to work out regularly.
The secret is in the exercise regime. The traditional, three-times-per-week sessions of weight training recommended for younger adults appear to be too frequent for aging bodies. Especially difficult are the eccentric muscle contractions—those that occur when a person lowers a heavy weight after lifting it, Bamman says. "The processes that stimulate protein synthesis and growth are activated most effectively in those contractions where you're putting the brakes on," he explains. But that direction of action is also the one that causes the most local inflammation and tissue damage. The researchers theorize that traditional weight training practiced twice per week, with an intervening session in which participants lift, but do not lower, weights, will be most effective. They are now starting a new five-year trial of that protocol and three others to find the optimum exercise "prescription" for older women and men.
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"I would love for people to begin to appreciate that an exercise prescription can be approached exactly like a drug prescription," says Bamman. "There's a proper dosage and a time course for it to wash out."
Most medical societies recommend a generalized exercise prescription, "but I'm not ready to accept that as the best method based on the work we've done," Bamman says. "We know, for example, that what is best for young people and old people is not the same, and I would suspect that's true for any disease you're trying to counteract. You can titrate this and identify what is best for type-2 diabetes, high blood pressure, cancer prevention, improving bone density, osteoporosis—whatever the case may be."