Sometimes I dreamt I was flying - not running, but flying. I need liberty

Pascal Delavaux, volunteer

The study was part of an ongoing programme, supported by the European Space Agency (Esa), which was intended to simulate the effects of weightlessness on the human body.

Scientists want to discover the best regime of drugs and exercise to keep astronauts fit on long-distance spaceflight. This could be a lengthy tour on the International Space Station (ISS) or a mission to the planet Mars.

But the results should also have benefits on Earth. The scientists say the work could lead to new exercise programmes for people who suffer from the brittle bone condition osteoporosis.

Blood flow

Fourteen male "guinea pigs" were confined to bed for 90 days, lying in a strict six-degree head-down tilt position.

They had to eat in this position, work at computers and even wash themselves on their backs. Cameras were trained on them 24 hours a day to make sure they did not get up and cheat.

Eating was even done lying down

Some of them did exercises in the horizontal position, designed to keep their bones and muscles strong. Another group was given medicine to achieve the same goal. A third group was used as a control, doing no exercise and receiving no medication.

The human body has evolved to take account of gravity. Take it away and people can experience bone wastage, and blood flow and digestion problems.

Pascal Delavaux, normally a teacher, watched his body waste away during the experiment and longed to be able to take exercise again.

"I need now to train, to run, to swim, to row, and it was impossible. Sometimes I dreamt I was flying - not running, but flying. I need liberty."

Future worlds

When the men took their first steps after 90 days lying on their backs, they had to be steadied by researchers - being weak-kneed and disoriented is exactly how astronauts feel when they return to Earth.

The volunteers had to be helped out of bed

The plans for the future exploration of our Solar System - which might include a manned mission to the Red Planet in the next 20 years - mean scientists need to learn how to stop people's bodies wasting away when they are in zero gravity.

Astronauts on the ISS do shifts of around three months; a future mission to Mars could take three years.

The 14 volunteers were subjected to their "ordeal" at the MEDES Institute for Space Medicine and Physiology in Toulouse.

Dynamic dancing

"These are only the first experiments - the first results," Professor Dieter Felsenberg, a senior scientist on the study, told the BBC.

"So, we can only demonstrate tendencies. In the group which did not exercise, 15% of bone mass was lost.

Professor Felsenberg said there were lessons in the study for the way osteoporosis patients were managed.

"We know there is a co-working between muscle and bone. From these types of experiments we know that osteoporotic people need to be trained, especially on their muscles so they can increase their muscle strength.

"Swimming or biking is not the real exercise for increasing muscle strength. What they have to do is dancing, for example; sports with high dynamic effort."