CAPE CANAVERAL, Fla. – Astronauts can become as weak as 80-year-olds after six months at the international space station, according to a new study that raises serious health concerns as NASA contemplates prolonged trips to asteroids and Mars.

Marquette University biologist Robert Fitts, who led the study, stresses that the accelerated space aging is temporary: Astronauts’ muscles recover after a few months back on Earth.

But what if a crew needed to make an emergency landing here on the home planet and rush from a burning spacecraft? What if after arriving at Mars, an urgent spacewalk was needed for repairs? Would the Mars men and women even be able to muster the strength for routine work?

“I’d be concerned,” Fitts said last week.

Astronauts can avoid becoming weaklings, however, with more research and the right equipment for hitting the space gym, Fitts observed.

Fitts bases his findings on calf muscle biopsies on nine U.S. and Russian space station residents from 2002 to 2005. It’s the first muscle study of long-flying astronauts that gets down to the cellular level.

Each astronaut spent six months aboard the orbiting lab and submitted to a biopsy before leaving and immediately upon returning to Earth.

The researchers discovered that the astronauts had lost more than 40 percent of the power in the slow-twitch fibers of their calf muscles. Those are the muscles so crucial for balance and posture.

Fitts said the muscle decline in the 40-something space station astronauts was equivalent to that of a person twice as old.