London, June 27 (IANS): It only takes two weeks of not using their legs for young people to lose a third of their muscular strength, leaving them on par with a person who is 40-50 years their senior, new research says.

"A young man, who is immobilised for two weeks loses muscular strength in his leg equivalent to ageing by 40 or 50 years," said Andreas Vigelsoe from University of Copenhagen in Denmark.

Weight training can help regain muscle strength after a period of physical inactivity, the study said.

The researchers examined what happens to the muscles in younger and older men after a period of high inactivity, by way of immobilisation with a leg pad.

"Our experiments reveal that inactivity affects the muscular strength in young and older men equally. Having had one leg immobilised for two weeks, young people lose up to a third of their muscular strength, while older people lose approximately one fourth," Vigelsoe said.

The researchers found that while young men lost 485 grams of muscle mass on average, older men lost approximately 250 grams.

"It is interesting that inactivity causes such rapid loss of muscle mass, in fact it will take you three times the amount of time you were inactive to regain the muscle mass that you have lost," said Martin Gram from University of Copenhagen.

After two weeks of immobilisation, the participants bicycle-trained three-four times a week for six weeks.

"Unfortunately, bicycle-training is not enough for the participants to regain their original muscular strength," Andreas Vigelsoe said.

"Cycling is, however, sufficient to help people regain lost muscle mass and reach their former fitness level. If you want to regain your muscular strength following a period of inactivity; you need to include weight training," Andreas Vigelsoe said.

The findings appeared in the Journal of Rehabilitation Medicine.