Scientists have found nutritional supplements can stop the muscle wastage associated with extended periods of physcial inactivity.
Muscle wastage is a problem for hospital patients
The loss of muscle strength can be a problem, for instance, for people confined to a hospital bed.
A University of Texas team were able to check the process by giving volunteers drinks containing essential amino acids and carbohydrates.
The study is published in the Journal of Clinical Endocrinology & Metabolism.
During the study 13 healthy male volunteers were confined to beds for a 28-day period.
Seven volunteers received the nutritional drinks three times each day, while six others were given a placebo with no nutritional value.
Using state-of-the-art methods to measure muscle volume and strength, the researchers found that the volunteers given the nutritional drinks retained all of their original leg muscle mass.
The members of the placebo group lost about a pound of leg muscle on average.
Those given the supplements also lost only about half as much leg strength as those given the placebo.
Lead researcher Dr Douglas Paddon-Jones said: "We thought it was the most astounding thing that even though our subjects did no exercise, they were able to maintain muscle mass."
The researchers believe a similar supplement regime could be of particular help for elderly people who face long stays in hospital, and for patients with severe trauma, who have a diminished ability to make new muscle tissue.
It may also reduce muscle loss in astronauts on long-duration space flights.
Dr Paddon-Jones said: "The elderly have less muscle to spare than the rest of us.
"When they get sick or injured and wind up in a hospital bed for a prolonged period, many of them lose so much muscle mass and strength that they don't get back up.
"For a lot of people, this supplement could make a real difference."
The researchers plan further investigations to determine whether nutritional supplements - alone and in combination with resistance or walking exercise - can indeed significantly reduce muscle loss in elderly men and women during prolonged bed rest.
Michael Rennie, professor of Clinical Physiology at Nottingham University and an expert in muscle wasting in the elderly, said the research was promising, but that the one pound loss of leg muscle in the control group was actually very small.
He said relying on nutritional supplements alone for elderly patients was unlikely to work, as his research had shown that they have a limited ability to utilise amino acids.
"It is important that elderly people receive proper nutrition in hospitals - which they don't - but they also need to be exercised and mobilised as much as possible," he said.
Professor Rennie said resistance exercises, such as pushing against a weighted chair, had been shown to be an effective way of minimising muscle wastage.
An hour a day of electrical stimulation had also been shown to prevent loss of muscle volume.