UB Study Shows Weightlessness Should Not Hinder Astronauts' Physical Activity In Space

BUFFALO, N.Y. -- Prolonged exposure to a weightless environment should not hinder astronauts from doing work requiring physical exertion in space, results of a new study by researchers at the University at Buffalo have shown.

Using subjects immersed head-out in water as a ground-based simulation of zero-gravity experienced in space flight, the researchers showed that the cardiovascular system adapts sufficiently to the conditions of simulated weightlessness to allow humans to perform work at all levels of exertion other than the maximum.

"These results show that astronauts in space, as well as divers who have to be in water for extended periods, should be able to carry out their work quite adequately, except for tasks that require the very highest level of oxygen metabolism," said David Pendergast, Ph.D., UB professor of physiology.

He noted, however, that reduced ability to perform tasks at maximum exertion levels after three hours of immersion, the time-period tested in the study, may suggest that longer exposures could decrease capacity further, perhaps compromising the body's ability to perform physical activity at near-maximal, as well as maximal levels.

The study appeared in the January issue of Aviation Space and Environmental Medicine.

Immersion in water is known to be a good simulation of weightlessness and to cause cardiovascular changes similar to those documented in space flight. While other under-water research has documented these changes, this study provides insight into how the human body might respond to increased metabolic demands in prolonged space flight, Pendergast said.

The study was carried out in the UB Center for Research in Special Environments, and involved seven male subjects who were fit, but not athletically trained. Each subject was tested in three phases -- in air, after 15 minutes of head-out immersion and after three hours of immersion.

Subjects sat on chairs while at rest and performed exercise on a cycle ergometer. They exercised at 20 percent, 40 percent, 60 percent, 80 percent and 100 percent of their maximum oxygen consumption. Researchers measured cardiac output, heart rate, stroke volume, blood pressure and oxygen consumption during rest and exercise at the various levels.

After 15 minutes of immersion, subjects showed elevated cardiac output, expanded plasma volume and increased dilation of the peripheral blood vessels, but these changes did not affect performance during exercise. The subjects were able to perform exercise equally well in water as in air.

After three hours of immersion, plasma volume and cardiac output had returned to pre-immersion levels. Cardiac stress was slightly higher during exercise, Pendergast said, but subjects remained capable of performing work up to 80 percent of their maximum oxygen consumption.

"Even though immersion causes immediate and profound cardiovascular changes, the adaptation to these changes over three hours does not seem to affect the system's ability to respond to submaximal levels of exercise stress," he said. "However, prolonged immersion can cause a loss of cardiac function sufficient enough to have a detrimental effect on the physiological response to maximal exercise."

Vincent D. Kame, a doctoral student in exercise science, assisted in the study, which was supported in part by a grant from the United States Navy, Office of Naval Research.