An 'exercise pill' could be developed after scientists discovered the proteins triggered by a gym session - by getting people to workout on one leg.
Almost 150 genes that boost muscle were isolated during the unique experiment that offers hope of developing medications to combat frailty in old age. It could now be developed into a wonder drug to mimic the benefits of a workout.
Project supervisor Professor Stuart Phillips said: "Building and retaining muscle is critical to overall health and quality of life. If we can target those genes with lifestyle and drug therapies, we may be able to help seniors and others vulnerable to muscle loss."
About half of over 65s in the UK live with some loss of strength that make everyday tasks a struggle. The key appears to lie in a set of 141 genes that regulate growth of the muscles and control power and movement.
In the study, published in Cell Reports, young and healthy men built up muscle in one of their legs through a prescribed regime of weight training.
For the first eight weeks, the other leg served as a non-exercising control. It was then completely immobilised with a brace during the last fortnight to keep it from bearing any weight.
In just two weeks, it lost the same average amount of muscle mass as the other had gained through two-and-a-half months of weight training.
The international team - which included British experts - compared gene responses of the muscles in the two legs to reveal those fuelling the muscle growth.
Muscle gains in the subjects' active legs ranged from one to 15 per cent over the full 10 weeks, averaging eight per cent. Meanwhile, muscle loss in their immobilised legs ranged between one and 18 per cent, averaging nine per cent.
In other words, the average subject lost muscle through inactivity at about five times the rate he had gained it through weightlifting.
Prof Phillips added: "The findings can be particularly useful for helping to keep seniors healthy and safe."
The research was supported by grants from the Natural Sciences and Engineering Research Council of Canada and the UK Medical Research Council.
