Healthy seniors benefit from strength training by rejuvenating their muscle tissue, say Canadian and U.S. researchers who found the proof at the molecular level.

Dr. Mark Tarnopolsky, director of the neuromuscular and neurometabolic clinic at McMaster University in Hamilton and Simon Melov of the Buck Institute for Age Research in Novato, Calif., compared tissue samples from 25 healthy older men and women who did six months of weight training and a similar group of 26 younger people.

'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.' —Study author Dr. Mark Tarnopolsky

The researchers looked at the molecular "fingerprint" of aging in mitochondria, the powerhouse that supplies energy to cells.Studies suggest poor mitochondrial function is involved in the loss of muscle mass and function commonly seen in older people.

Older adults showed a decline in gene activity for mitochondrial function, but exercise was linked to a reversal back to levels similar to those of younger adults, the team reports in Wednesday's issue of the journal PloS One.

Before exercise training, the older adults were also 59 per cent weaker than the younger adults, but after the training, their strength wasonly 38 per cent weaker.

After four months of follow up, most of the older adults were no longer exercising at a gym but continued to do resistance exercise at home by lifting soup cans or elastic bands.

"They were still as strong, they still had the same muscle mass," Tarnopolsky said in a release. "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."

Aging reversal

While aging studies on worms, fruit flies and mice have shown similar results, Melov said the researchers were surprised at the extent of the results in humans.

"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, which is an additional incentive to exercise as you get older."

The younger participants were 20 to 35 with an average age of 26, while those in the older group were all over 65 with an average age of 70. Both groups were similar in terms of diet and exercise, and none took medication or had diseases that affect mitochondrial function.

The hour-long resistance training sessions were done twice a week on standard gym equipment, involving 30 contractions of each muscle group.

Tissue samples were taken from the thigh muscle, and the strength test was based on knee flexion.

Future studies are planned to determine if resistance training has any genetic impact on organ tissues. The researchers also want to determine whether endurance training such as running or cycling affects mitochondrial function and aging.