They will not be allowed to get up, not even once, for a breath of fresh air, a change of scenery, a shower or to use the toilet.
As we age, our bodies lose bone density and muscle strength. Astronauts in space suffer similar changes but at a much faster rate than on Earth.
Finding ways to combat this process is important to space agencies, hospital patients and everyone who plans on growing old.
The research is part of a wide range of international bedrest studies that aim to develop and test countermeasures to the challenges of living in space, ageing and long periods of immobilisation after illness.
Putting people in bed lying with their heads 6° below the horizontal for long periods causes their bodies to react in similar ways to being weightless, but is cheaper and safer than sending them into space.
The control group will spend 21 days in bed without any countermeasures, while a second group follows a schedule using resistive and vibrating exercise machines.
The last group will use the exercise machines and eat nutritional supplements of whey protein - a common supplement used by bodybuilders to train their muscles.
The healthy volunteers will participate in all the regimes one after the other over the course of the entire experiment of more than a year.
The volunteers will have four months between each bedrest session to recuperate, get some real rest and appreciate getting out of bed in the morning.