​2-week inactivity may leave kids with pensioner’s muscle strength – study

Parents who allow their kids to ditch football practice for video games may want to re-think their strategy. A new study says it only takes two weeks for children to lose one-third of their muscle strength, putting them on par with someone 50 years older.

The research, conducted by the Center for Healthy Aging and the Department of Biomedical Sciences at the University of Copenhagen and published in the Journal of Rehabilitation Medicine, immobilized one leg of both younger and older men by attaching a pad to that limb.

To determine the effects of immobilization on muscle mass, the researchers measured maximal voluntary contraction, leg work capacity, and leg lean mass by dual energy X-ray absorptiometry. Muscle biopsies were also performed, and were evaluated for fiber type, fiber area and capillarization.

The findings showed that it took just two weeks for the young participants to lose one-third of their muscle strength, leaving them with the same physical ability as someone 40 to 50 years older.

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That loss in muscle strength is very similar to what is found in older men, according to researcher Andreas Vigelsoe.

“Having had one leg immobilized for two weeks, young people lose up to a third of their muscular strength, while older people lose approx. one fourth,” Vigelsoe said in a university press release.

The research also stated that while both young and older men lose muscle mass when immobilized for two weeks, young men lose more – 485 grams compared to 250 grams. However, young men have more to lose in the first place, as they carry approximately 1kg more muscle mass in each leg than older men.

But the “loss of muscle mass is presumably more critical for older people, because it is likely to have a greater impact on their general health and quality of life," researcher Martin Gram said.

Once the two-week immobilization period was over, the participants trained on a bicycle three to four times a week, for six weeks. Cycling was enough to regain muscle mass, but not muscle strength.

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

And although biking aided with the return of muscle mass, re-gaining it wasn't as quick or easy as losing it.

"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. This may be caused by the fact that when we're inactive, it's 24 hours a day," Gram said.