Overview of the NASA 70-day Bed Rest Study.

The purpose of this article was to provide an overview of the National Aeronautics and Space Administration (NASA) 70-day Bed Rest Study. The integrated complement of investigations and the standardized bed rest environment that served as the platform for this study complement are described. Outcomes of the studies will not be presented here but will be reported in separate publications. A set of studies running in an integrated fashion along the entire period (pre-, in-, and post-bed rest) and using the same subjects is referred in this article as "the campaign" or "complement." NASA selected eight individual studies to participate in the 70-d bed rest campaign. These studies were integrated to increase efficiency in the utilization of resources and to share common measures among the investigations. In addition to the individual studies addressing specific aims, a battery of standardized measures was included. Standard measures target a wide range of physiologic systems and represent some of the testing routinely done on astronauts. Bed rest subjects underwent rigorous medical and psychological screening. Standardized conditions included 70 d of bed rest in a 6° head-down tilt position. Subjects' vital signs, body weight, and fluid intake and output were measured daily. A standardized diet was provided to ensure consistent nutritional intake across subjects. Exercising subjects were prescribed individualized aerobic and resistance training 6 d·wk performed in a horizontal body position. Subjects in the testosterone supplementation countermeasure group received testosterone enanthate injections at 2-wk intervals during bed rest. Long-duration head-down tilt bed rest provided a suitable platform for examining physiologic effects of spaceflight and testing countermeasures in a ground-based model. Integrating studies into a complement is an effective way to support multiple investigations while minimizing the number of subjects to answer many research questions.