Human adaptation to simulated gravitational fields

We present the resuIts of manned studies in which test subjects were exposed to simulated zero g (water immersion or head-down tilt at -6 degrees) and head-to-feet acceleration. The findings give evidence that humans have different individual tolerances to an acceleration of +3 Gz after exposure to zero g, whether simulated by immersion or by head-down tilt. The paper discusses the role of functional relationship between water balance and cardiac output in the establishment of adaptive reactions to simulated zero g.