updated 9/14/2009 12:23:25 PM ET 2009-09-14T16:23:25

It’s a sad fact that muscles shrink as adults age. But new studies are starting to unravel how this happens — and what to do about it.

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Past research has shown that the bodies of older people build muscle from food less efficiently than young people. Now researchers at the University of Nottingham in England have also found that a mechanism that prevents muscle breakdown works less effectively in people over the age of 65, resulting in a “double whammy” effect.

For the elderly, less muscle mass means not only a loss of strength, but also increases the likelihood of injuries from falling. However, the new research suggests weight training may help older people retain muscle.

The study, detailed in The American Journal of Clinical Nutrition, compared the effects of insulin (a hormone released to slow muscle breakdown after eating) on a group of people in their late 60s to a group of 25-year-olds.

The subjects were examined before breakfast and then re-examined after they were given a small amount of insulin to raise the hormone to a level similar to having ate a bowl of cornflakes or a croissant.

To calculate how much “wasting” was happening in the leg muscles of both groups, the researchers tagged an amino acid (a building block of muscle protein) and performed blood analysis to determine how much of the amino acid was delivered to the leg and how much was leaving it.

“The results were clear,” explained Michael Rennie, a professor of clinical physiology at the University of Nottingham. “The younger people’s muscles were able to use insulin we gave to stop the muscle breakdown, which had increased during the night. The muscles in the older people could not.”

The researchers also noticed during the course of the study that the blood flow in the leg was greater in the younger people than the older people. This suggests that the supply rate of nutrients and hormones is lower in the older people and may explain why muscle wasting occurs, says Rennie.

In a follow-up study, the research team found that three exercise sessions a week over 20 weeks was enough to reverse muscle wasting by increasing blood flow to the legs of older people to a level identical to the younger group.

“I am extremely pleased with progress,” Rennie said. “It looks like we have good clues about how to lessen it with weight training and possibly other ways to increase blood flow.”

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