The objective of this study was to valid a water immersion model for microgravity and to study the effects of simulated condition on salivary cortisol and a-amylase.Increased activity of stress systems is reported during space flight, but unchanged or decreased activity during simulated microgravity. We here investigated the impact of head-out water immersion on the activity of the hypothalamus-pituitary-adrenal axis and the sympathetic-adrenal-medullary system. The healthy young men were exposed to a nine -hour water immersion in a thermo neutral bath and a control condition. Saliva samples were taken before, during, and after interventions to assess cortisol as an index for hypothalamus-pituitary-adrenal axis activity, and salivary a amylase as  an index for sympathetic-adrenal-medullary system activity. Cortisol and Amylase levels uniformly increased during simulated conditions. In conclusion, Both systems activity shows initial increased during water immersion. 

Key words: Simulated microgravity, salivary cortisol, salivary a-amylase, water immersion model.