The multifunction exercise machine would let astronauts work against hydraulic pressure while doing exercises similar to those that require weight slacks on Earth, according to Greenisen, manager of the exercise countermeasures program for the National Aeronautics and Space Administrations NASA wants exercises that stress the body from the shoulders to the feet, Greenisen said. Astronauts would press against the machine's yoke-like collar.

The program's goal is to give astronauts a workout equivalent to a day's worth of gravitational pull on earthbound bones and muscles, Greenisen said. It's based on a mathematical model, which can be fitted to the individual astronaut, of how much force a day's worth of gravity would be, he said.

In weightlessness, it's no problem to be out of shape, Greenisen said: "The human body adapts perfectly to the space environment." What happens after space is the problem. Astronauts' muscles must be strong enough to reencounter gravity -- either the Earth's or that of some other planet, Greenisen said. Astronauts typically end space shuttle missions weak and wobbly under the combined loads of their 75-pound launch and entry suits and their own body weights, he said.

Another purpose is to retard the loss of bone mineral density. Without the stress of gravity, bones lose calcium, as people do when they are confined to bed. If the bones are stress-free long enough, the weakness can increase the risk of fractures. Finding exercise for long flights will be crucial for interplanetary flight, Greenisen said. Unless astronauts can stay strong enough to function after they re-encounter gravity, those missions can't go forward, he said.

And stationary bikes, rowing machines and treadmills, all tried in space, haven't been able to do the job. These machines are primarily valuable for cardiovascular conditioning; they make less powerful demands on bone density and muscle power. So NASA, working with Ariel Dynamics, Inc. of Trabuco Canyon, Calif., has created a prototype resistance exercise machine. The device, about one foot square and two feet high, is made of steel and weighs about 70 pounds, but the weight could be dropped below 50 pounds if it is made of titanium, Greenisen said.

So far, the device has been tried by astronauts and scientists who worked out in a NASA plane as it dived, Greenisen said. These tests in 20-second bursts of free-fall weightlessness indicated the machine could create enough force to mimic gravity, he said. Greenisen awaits the scheduling of a space shuttle trip in which to test the device. He wants to answer such questions as whether one session of exercise will do the gravity-imitating job or whether exercise should be scheduled in smaller segments throughout the day. The problems of bone and mineral loss in space are the same ones faced on Earth by people confined to bed, So NASA also has been studying how to exercise while in bed.

For now, the equipment developed with Ariel has the inside track to space partly because its hydraulic equipment requires less area. Greenisen said. It would not need an air compressor that Kaiser's pneumatic equipment would use, he said.

End Advance for Monday, April 17, and Thereafter