Fans of the 1968 movie 2001: A Space Odyssey will recall this scene depicting exercise in orbit:
(2001: A Space Odyssey)
This is a very costly strategy to implement in real life on a space craft, or even a space station. Alan Hargens, an orthopaedic surgeon at the University of California, San Diego has developed the lower body negative pressure (LBNP) device. He describes it as “an early form of artificial gravity”.
“A centrifuge is probably the best thing we could give the astronauts, but it’s very expensive and there are also some safety issues with having a rotating device on a spacecraft,” he said. “This device works like a vacuum cleaner, so the person can exercise at their normal body weight.”
(Lower body negative pressure (LBNP) video)
Astronauts have tested the device in ground-based studies and it has been shown to counteract muscle and skeletal problems in studies involving prolonged bed rest – a proxy for spending time in low gravity...
Hargens and colleagues believe a compact, collapsible version of the device could be used on an extended space mission to the moon or Mars.
“For crew mental wellbeing, the system could include a virtual environment to simulate walking and running with family members on the beach or in mountains,” said Hargens. “Importantly the concept would also allow normal weight-bearing in seated posture on a prolonged mission using the suction pressure to reproduce the posture that we assume 12 to 16 hours each day on Earth.”
NASA describes the device as follows:
The lower body negative pressure test places a stress on the cardiovascular system very similar to the one experienced when standing in Earth's gravity.
The crew member is placed in the lower body negative pressure device. The tube covers the astronaut from the feet to the waist and an airtight seal is made around the waist. A pump then sucks air from the tube which creates a negative pressure inside the tube and hence around the legs of the subject. This in effect pulls blood from the upper part of the body to the legs. The pressure is lowered for about 50 minutes during which measurements are made.
The lower body negative pressure device is a cylinder that encloses the lower abdomen and lower extremities to maintain a controlled pressure differential below ambient during periods of extended weightlessness.
In his 1953 novel Space Tug, Murray Leinster wrote about a gravity-simulator harness for astronauts to maintain a good level of fitness:
"When we got back," Joe told Brown, "we were practically invalids. No exercise up here. This time we've brought some harness to wear. We've some for you, too..."
Joe got out the gravity-simulator harnesses. He showed Brent how they worked. Brown hadn't official instructions to order their use, but Joe put one on himself, set for full Earth-gravity simulation.
He couldn't imitate actual gravity, of course. Only the effect of gravity on one's muscles. There were springs and elastic webbing pulling one's shoulders and feet together, so that it was as much effort to stand extended—with one's legs straight out—as to stand upright on Earth. Joe felt better with a pull on his body.
(Read more about Leinster's gravity-simulator harness)