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If you want a taste of the Fountain of Youth, try pumping iron. That's the message that emerges from a new Canadian study that shows that resistance training actually reverses aging - at least in muscle tissue.

"With a little weight training we managed, to a certain extent, to turn back the hands of time," Mark Tarnopolsky, director of the neuromuscular and neurometabolic clinic at McMaster University in Hamilton and co-author of the study, said in an interview.

"Resistance training reversed the effects of aging in skeletal muscles," he said.

Participants in the research project, who lifted light weights for a mere two hours a week, were able to improve their muscle strength by 50 per cent during the six-month study period.

Researchers, however, did not merely measure muscle strength in the traditional sense of the term.

Rather, they measured the gene expression of muscles - more specifically how many mitochondria they produce.

Mitochondria are tiny biochemical power plants in cells that convert food into energy, and tiny changes in mitochondrial DNA have been pegged as the key component of aging.

"The reason we get weaker, thinner and have less endurance as we age is that there are fewer genes making mitochondria," Dr. Tarnopolsky said.

Loss of muscle mass is a major problem among seniors, leaving many frail; about one in four people over 80 have lost so much muscle mass that they cannot carry out many activities of daily living.

But the new research suggests that process can be slowed, or even reversed, by stimulating muscles with weight training. (A future study will examine if endurance training, such as running or cycling, has similar effects.)

To conduct the study, which is published in today's edition of the online medical journal Public Library of Science, researchers recruited 25 healthy seniors (average age 70) and an equal number of university students (average age 26.) They all had muscle biopsies and 24,000 genes were compared in each participant; 600 genes were markedly different between the older and younger participants.

At the outset, both groups had similar activity levels but the young people were, not surprisingly, much stronger.

Initially, the seniors were 59 per cent weaker than the young adults. But after six months of twice-weekly weight training, they were 38 per cent weaker.

More important, the gene expression profile (or genetic fingerprint) of the seniors had changed noticeably, looking a lot more like that of the younger folk.

"We were surprised by the results," said Simon Melov, director of genomics at the Buck Institute for Age Research in Novato, Calif., and co-author of the study.

"We expected to see gene expressions that stayed fairly steady in older adults. The fact that their genetic fingerprints so dramatically reversed course gives credence to the value of exercise not only as a means of improving health, but of reversing the aging process itself," he said.

Barbara Ford, a 72-year-old retiree and study participant, said that she is not conversant with the science but that there's no question she feels healthier and younger as a result of the weight training.

"I don't know exactly what they were after with the muscle biopsy and their tests, but I can tell you I don't feel 72. I don't feel a day over 60."

Mrs. Ford said she recognizes that being active, physically and mentally, is essential to good health, but having an established program in the gym made it a lot easier to do so, and weight training was a lot more fun that she would ever have imagined.

"It was a great experience. I felt stronger and had more stamina. My grandchildren said I had Popeye muscles," she said with a laugh.

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