Physiological changes associated with long-term increases in acceleration.

The long-term retention of organisms in increased acceleration fields is an experimental approach towards understanding the biological consequences of earth gravity. Such treatment, called chronic acceleration, simulates a change in gravity and requires exposed organisms to adapt physiologically to the new environment. Information from chronic acceleration supplements that from space physiology in understanding gravitational physiology. Many of the responses in long-term exposure to increased acceleration are those which would be anticipated from the imposed symmetrical loading. For example, increased requirements for posture and locomotion induce appropriate changes in musculo-skeletal organs. Displacement of body fluids and increased hydrostatic pressures lead to greater blood volumes and increased tissue hydration. However, there are also specific acceleration effects which cannot be so directly interpreted. Among these are decreases of mature body size and of depot fat, which are proportional in degree to field strength. The role of chronic acceleration research in the development of gravitational biology and its relationship to earth-orbital experiments are considered. The applicability of chronic acceleration studies with human subjects towards planning of deep space exploration is also discussed.