Even if we could farm on Mars, astronauts might be too weak by the time they get there to help plow the fields.

The first cellular analysis of muscles from astronauts who have spent 180 days at the International Space Station shows that their muscles lost more than 40 percent of their capacity for physical work, despite in-flight exercise.

No matter how good their shape was before the astronauts left, they returned with muscle tone that resembled that of the average 80-year-old. In fact, the astronauts who were in the best shape before they launched were the most likely to come back with withered, or atrophied, muscles.

NASA currently estimates it would take a crew 10 months to reach Mars, with a one year stay, and 10 months to get back, for a total mission time of about three years. These studies suggest they would barely be able to crawl by the time they got back to Earth with the current exercise regime.

"The lack of load" – pressure on muscles – "is the main problem," said biologist Robert Fitts of Marquette University. "There is no gravity and so any fibers within those muscles are unloaded. The load normally maintains protein synthesis and the size." Even with plenty of activity, the lack of load leads to atrophy.

In an Aug. 17 Journal of Physiology study, Fitts' team tested muscle fibers from calf biopsies of nine astronauts, taken before and after their space station stay. The researchers isolated single muscle strands and tested their ability to generate force and velocity.

On average, astronaut muscle lost 35 percent of its capacity to produce force, and 20 percent of its velocity. Both of these factors contributed to a 45 percent loss in power required for strong, quick motions.

The study is a follow-up to an earlieranalysis of muscle size, where the researchers put the loss of muscle volume at 15 percent.

Since that study, scientists have developed what they hope will be a better workout device for space, called the Advanced Resistance Exercise Device, or aRED, which was sent to the ISS last year. The device offers more resistance than the previous workout regimen.

"I know the crew has been using the aRED, but as of now there has been no test to see whether it has been effective," Fitts said. "Although they’ve been proposing to test it on ground using bedrest studies, those haven’t gotten anywhere. The first way to test these studies would be a well controlled bedrest study."

Bedrest studies are where study participants spend 90 days in bed, the closest thing scientists have come up with for recreating space like conditions on earth.

Despite the wasting measured in this study, Fitts is optimistic.

"I'm convinced that with the right device we can prevent this wasting in space," he said.

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Image: NASA

*Citation: Fitts et al. "Prolonged Space Flight-Induced Alterations in the Structure and Function of Human Skeletal Muscle Fibers." The Journal of Physiology, August 17. *