If men ever do land on Mars, they could be too feeble to do anything much when they get there, according to new research.
NASA currently reckons it would take a crew ten months to reach Mars with a one year stay, meaning a total mission of approximately three years.
But a new study led by Robert Fitts of Marquette University has found that astronauts' muscles would waste away severely on long space flights, reducing their capacity for physical work by more than 40 percent.
That's the equivalent of a 30- to 50-year-old crew member's muscles deteriorating to the level of those of an 80-year-old.
Fitts believes that if astronauts were to travel to Mars today their ability to work would be compromised. With the most affected muscles, such as the calf, the decline could approach 50 percent.
Crew members would get tired more rapidly and have difficulty performing even routine work in a space suit. Even more dangerous would be their return to Earth, where they'd be physically incapable of evacuating quickly in an emergency landing.
The study – the first cellular analysis of the effects of long duration space flight on human muscle – took calf biopsies of nine astronauts and cosmonauts before and immediately after 180 days on the International Space Station (ISS).
The results showed substantial loss of fibre mass, force and power.
Starting the journey in better physical condition didn't help - indeed, the crew members who had the biggest muscles to start with showed the greatest decline.
According to Fitts, the results show a need to design and test more effective exercise programs on the ISS before embarking on distant space journeys. They would need to involve high resistance and a wide variety of motion.
He doesn't feel scientists should give up on extended space travel, though.
"Manned missions to Mars represent the next frontier, as the western hemisphere of our planet was 800 years ago," says Fitts. "Without exploration, we will stagnate and fail to advance our understanding of the universe.'
In the meantime, Fitts believes efforts should be on making the most of the ISS so that better methods to protect muscle and bone can be developed.
"NASA and ESA need to develop a vehicle to replace the shuttle so that at least six crew members can stay on the ISS for six to nine months," he says.
"Ideally, the vehicle should be able to dock at the ISS for the duration of the mission so that, in an emergency, all crew could evacuate the station."