One small step for man . . . while he is suspended in midair, using a treadmill mounted on the wall.

University researchers have developed a device that simulates weightlessness to test various exercises for use in space.

The University's Center for Locomotion Studies began working on the zero gravity simulator three years ago after receiving a grant from the National Aeronautics and Space Administration, said Brian Davis, assistant professor of biobehavioral health.

The simulator was developed to compare different treadmills, Davis said. The device will not be used in space -- it was developed only to simulate weightlessness to find a good form of space exercise, he added.

"We tried to come up with a way to run that would cause the body to experience loads like it does on earth," Davis said.

When people go into space their bodies adapt to weightlessness, Davis said. The person can float, making leg bones basically useless, he said.

"It's not immediate but within about 12 hours, they will begin to lose the calcium in their legs," Davis said. "There's two things to do -- you can either let it happen and get severely weak or try to do something about it."

After six months in space, calcium loss could be up to 20 percent, Davis said.

Muscle mass, blood pressure and fluid distribution are also affected, he said, adding that these losses make exercise imperative.

Reducing calcium loss is not easy, Davis said. Calcium supplements and different drugs have been tried, but exercise has so far been the best solution, he said, adding that running could be effective.

When a person runs on Earth, the heel and lower leg cushion most of the shock, Davis said. But there is almost no impact force in zero gravity because runners in space land on the balls of their feet, he added.

"It's just our theory, but if you can exercise in space and subject the bones to impact, perhaps it would slow down the calcium loss," Davis said.

Passive treadmills are currently used on the space shuttles because they are light, small and do not need power to run, Davis said. On Skylab, the astronauts only had a piece of plastic and springs to hold them down, he added.

"It's funny that something so primitive was used in such high technology," he said.

It takes about 90 minutes to put a subject into the simulator for a test run, said Randall Bock, technical coordinator. The volunteer is suspended horizontally by bungee-like cords attached to the arms, legs, torso, chest and head in 11 places. A series of pulleys allows the subject to move freely.

The subject then goes through a series of running and jumping motions to test impact, which is measured by a scale underneath the treadmill mounted vertically on a wall.

Bock, who was the first to test the device, said he felt a greater freedom in his limbs while he was in the harness, similar to what the astronauts must feel in space.

"It feels like you're floating in water," Davis said.

Safety was an important factor in designing the simulator, Bock said. The subjects had to be able to move but have adequate support at the same time, he said. A mat is placed under the subject for additional safety.