Astronauts on a mission to Mars could lose nearly half their muscle strength during the long trip, giving them the physiques of senior citizens by the time they arrived, according to a new study.
Prolonged exposure to weightlessness could cause astronauts to lose more than 40 percent of their muscle strength even with regular exercise, researchers said. On a long voyage, a healthy 30- to 50-year-old astronaut could end up with the strength of an 80-year-old.
A 10-month trip to Mars would cause such extreme muscle deterioration that astronauts would find it difficult to perform even routine tasks, let alone move around the Martian surface in spacesuits, according to the study, which was led by Robert Fitts of Marquette University.
Returning to Earth could be even more perilous, the researchers found: The astronauts could be too weak to evacuate their spacecraft if they needed to make an emergency landing.
The research is detailed in the Aug. 17 edition of the Journal of Physiology.
The need for better exercise
Fitts, a biological science professor at the university in Milwaukee, and his team concluded the development of better, more effective space exercise regimes would be vital for any manned spaceflight to Mars or another planet.
Fitts and his team studied the effects of long-duration space missions on astronaut muscles by taking samples from nine International Space Station astronauts and cosmonauts. The samples were taken before and after the astronauts and cosmonauts' 180-day missions aboard the space station.
Just being strong was no defense, the researchers found. In fact, the astronaut with the biggest muscles experienced the most severe deterioration.
The drill in orbit
The physical toll of space missions is no surprise to NASA. The space agency has long known about the problem, and astronauts routinely train hard to stave off the worst effects of muscle-wasting in space.
During their six-month stints aboard the International Space Station, astronauts exercise about 2.5 hours per day, six days a week, said Lori Ploutz-Snyder, an exercise physiologist at NASA's Johnson Space Center.
"Exercise is a big part of their day," she told Space.com. "It's a big part of our program."
The training regimen aboard the space station involves three components: a stationary bike, a treadmill and a fancy machine called the Advanced Resistive Exercise Device. Installed in November 2008, the ARED allows astronauts to perform a variety of weight-training exercises, such as squats and bench presses, with loads of up to 600 pounds.
How do astronauts weight-train in zero gravity? Ploutz-Snyder said the ARED generates loads using vacuum cylinders. It also has flywheels to generate the inertia needed to get the load off the rack.
Running in weightlessness
Trotting on a treadmill in space isn't so easy, either.
"If you weren't strapped in when you pushed off, you'd just float away," Ploutz-Snyder said. So astronauts using the space station treadmill wear a special harness tethering them to the machine. Bungee cords provide adjustable loading, simulating walking in a non-weightless environment.
And the training doesn't stop when the mission ends. After they return to Earth, NASA puts its astronauts through a customized exercise program that emphasizes strength and aerobic fitness.
"They essentially have their own personal trainer," Ploutz-Snyder said.
Most astronauts stay in this personalized fitness program for a month or so, but some keep at it for 90 days. It all depends on how they feel when they land, and what a team of doctors and exercise physiologists thinks is best.
The new Journal of Physiology study recommends that astronauts in zero gravity focus on high-resistance exercise to keep their muscles from wasting away. Ploutz-Snyder says that's just what the space station's ARED machine will deliver.
"We're just getting started on our new research program with higher-intensity exercise," she said. "In a couple of years we'll start to get an idea of how it's working."