Just two weeks of not using their legs causes young people to lose a third of their muscular strength, placing them on par with someone 40-50 years their senior, new research has found.

A new study by The Center for Healthy Aging and the Department of Biomedical Sciences at the University of Copenhagen has shed fresh light on the dangers of not exercising. Their findings, published in the Journal of Rehabilitation Medicine, conclude that a fortnight of inactivity also causes ‘rapid loss of muscle mass’.

The study – which sought to explore the impact of high inactivity caused by being injured, ill or take a very relaxing holiday by immobilising a participant's’ leg in a pad – also demonstrates the dangers of simply spending excessive amounts of time on the couch.

"Our experiments reveal that inactivity affects the muscular strength in young and older men equally,” said Andreas Vigelsø, PhD, one of the researchers.

“Having had one leg immobilised for two weeks, young people lose up to a third of their muscular strength, while older people lose approximately a quarter. A young man who is immobilised for two weeks loses muscular strength in his leg equivalent to ageing by 40 or 50 years."

The research also found that young people lose twice as much muscle mass as older people over the two week immobilisation period, while physical fitness was also reduced.

Another striking finding was the amount of time required to recover from such a period of inactivity. After two weeks of immobilisation, the participants bicycle-trained 3-4 times a week for six weeks, but although this helped return muscle mass, it was found that additional weight training is required to regain muscular strength.

"It’s interesting that inactivity causes such rapid loss of muscle mass, in fact it’ll take you three times the amount of time you were inactive to regain the muscle mass that you’ve lost,” said Martin Gram, PhD, another of the researchers. “This may be caused by the fact that when we’re inactive, it’s 24 hours a day."