Antiorthostatic hypokinesia as a method of weightlessness simulation.

Physiological effects seen in eight test subjects during a 5-d bedrest experiment in the head-down position (0,-4,-8,-12degrees) were studied. It was shown that the antiorthostatic hypokinesia at -12degrees could reproduce physiological responses shown by space crewmembers more closely than recumbent bedrest. Our observations help to stimulate an acute stage of human adaptation to the weightless state and to assess the part played by gravity-induced blood redistribution in the development of physiological changes.

Functional insufficiency of the neuromuscular system caused by weightlessness and hypokinesia.

The results of study of the crew members of the spaceships Soyuz are described, and the effects of weightlessness on reflex excitability, muscular tone and muscle contractibility discussed. A certain decrease in postural muscular tone and strength, increase in reflex excitability at rest and increase in bioelectric activity of muscles at work has been found in the cosmonauts after their stay in a weightless environment. The circumference of the lower extremities decreased.