Abstract: In order to examine the adaptive capacity of humanbody for bearing weightlessness (WL),the 4h head-down 15° bed-rest was used to simulate WL.The tolerance time and the changes of REG during bed-rest for 38 subjects were observed.The result is that the regular changes of REG which reflect the state of brain circulation are found during the tes- ting and it associated with the subjects' tolerance time.The results indicated that the method of short time head-down bed-rest is an effective approach to examine the adaptive capacity of subjects for bearing WL and the REG is a valuable index.

Key words: Weightlessness simulation, Weightlessness physiological effect, Test