LONDON- Gym training can rejuvenate the muscles of pensioners in a way that appears to reverse ageing, a study has shown.
Astonished researchers found that muscle tissue actually seemed to become younger.
Some 25 over-65s, with an average age of 70, took part in the study and trained at a gym.
Not only did they acquire new strength, but the molecular machinery powering their muscles became as active as that seen in people of 20 or 30.
In the first study of its kind, the Canadian scientists measured gene activity in tissue removed from the pensioners' thighs and compared it with samples from a group of 20 to 35-year-olds.
Dr Simon Melov, who co-led the research at McMaster University Medical Centre in Hamilton, Ontario, said: "We were very surprised by the results of the study. We expected to see gene expressions that stayed fairly steady in the 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 ageing process itself."
Young and old volunteers had similar diets and levels of daily exercise, and none took medicines or had diseases that might have affected the study results.
The older participants were put through six months of resistance training using standard gym equipment. Twice-weekly sessions were held, each an hour in length, which involved 30 contractions of each muscle group.
Measurements of muscle strength showed that before training, the pensioners were on average 59 per cent weaker than the young adults. Afterwards, they were only 38 per cent weaker - an improvement of almost 50 per cent.
But the most remarkable change was hidden in the mitochondria, the rod-like 'power plants' that sit within every cell and generate energy.
Numerous studies have indicated that mitochondrial dysfunction is involved in the muscle loss and functional impairment seen in older people.
Measuring gene "expression", or activity, in the mitochondria allowed the scientists to shine a light on one of the key elements of ageing.
They found that exercise reversed this genetic fingerprint back to levels similar to those seen in the young volunteers.
Four months after the study was completed, most of the pensioners were no longer going to a gym, but carrying on simple lifting exercises or working with elastic bands at home.
"They were still as strong, they still had the same muscle mass," said Dr Mark Tarnopolsky, another member of the McMaster team.
"This shows that it's never too late to start exercising and that you don't have to spend your life pumping iron in a gym to reap benefits."
The findings were reported in the on-line journal PLoS One.
The scientists are designing further studies to find out whether resistance training has any genetic impact on organs and other types of tissue.
They also want to investigate the effect of endurance exercise, such as running or cycling, on mitochondrial function and the ageing process.
Looking at gene expressions could provide the starting point for developing drug therapies that affect ageing.
Dr Melov said: "The vast majority of ageing studies are done in worms, fruit flies and mice; this study was done in humans.
"It's particularly rewarding to be able to scientifically validate something practical that people can do now to improve their health and the quality of their lives, as well as knowing that they are doing something which is actually reversing aspects of the ageing process."