At last the key to eternal youth - go to the gym!

According to scientists the secret of eternal youth is not to be found in a bottle of pills or some kind of potion; it is they say as simple as working out at the gym on a regular basis.

The Canadian researchers say they have found that seniors who regularly use weights have almost as much energy as people less than half their age.

Apparently as little as six months of gentle weight training will turn back one of the body's molecular clocks and rejuvenate ageing muscles to the extent that they are almost as powerful as those found in someone much younger.

Dr. Simon Melov says the research gives credibility to the benefit of exercise, not only as a means of improving health but of reversing the aging process itself.

Dr. Melov, a Buck Institute faculty member at McMaster University Medical Center in Hamilton, Ontario, is an expert on how ageing affects the body.

Along with Dr. Mark Tarnopolsky, he conducted a study examining how exercise affected the muscles of a group of pensioners.

The training was done on standard gym equipment, in twice-weekly sessions of an hour, involving exercises commonly offered in training sessions at most fitness centers.

The strength test was based on knee flexion.

The study involved 25 healthy older men and women men and women all over age 65, who were recruited at McMaster University and were matched with a younger group with an average age of 26 in terms of diet and exercise.

None of the participants were on any medication or had diseases that can alter mitochondrial function.

The researchers took tissue samples from their thigh muscles and found that after six months, the pensioners, were much stronger than before but of even more interest was the natural process of muscle aging seemed to have been reversed.

As a rule the mitochondria, the tiny powerhouses that generate energy within cells, become less active as a person ages.

However the researchers found exercising reinvigorated the muscle mitochondriain in the men and women studied to such an extent that by the end of the study the tiny structures were almost as powerful as those found in people aged just 20 or 30.

Dr. Tarnopolsky says even though most of the seniors had given up the gym within four months, they continued to exercise using household items as make-shift weights and were still as strong with the same muscle mass.

The researchers say it is never too late to start exercising and they now intend to look at whether running, cycling and other forms of exercise that build stamina rather than strength, have the same effect.

Dr. Melov says the majority of ageing studies are done in worms, fruit flies and mice but this study was done in humans and is particularly encouraging in that it scientifically validates practices which people can do to improve their health and the quality of their lives which also reverse aspects of the aging process.

The research is published in the journal PLoS ONE.