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Older people lose substantial amounts of skeletal muscle when they stay in bed for more than a week, according to an experiment in healthy volunteers. Twelve men and women with a mean age of 67 had a series of tests before and after being confined to bed for 10 days. They ate a standard diet containing the recommended daily amount of protein. Muscle protein synthesis decreased by 30% during the experiment (95% CI 7% to 54%) and they lost a mean of 1.5 kg of lean body mass (0.62 to 2.48). Most of the loss was from their legs, which became significantly weaker as a result. The volunteers' nitrogen balance was negative even before the experiment started, but it fell further during bed rest, despite the balanced dietdiet.
These volunteers were healthy and reasonably active, say the researchers. The adverse effects of 10 days in bed are probably even greater for older people in hospital who have the added disadvantages of physiological stress and poor diet. Loss of muscle mass could help explain why many older people experience functional decline when in hospital. In this experiment, healthy older people lost more lean tissue in 10 days than younger people would be expected to lose in a month.