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Metabolic energy requirements during manned orbital Skylab missions.

An investigation was undertaken to determine the metabolic cost of life in space. Energy intake was determined throughout the 28-, 59- and 84-day flights for each of the nine Skylab astronauts. Metabolic excretions were quantitatively collected and analyzed for a variety of biochemical constituents. Body mass was determined each day and body volume was ascertained by stereophotogrammetric means immediately pre- and post-flight. A ground-based control period of at least 3 weeks preceded each flight, and one of at least 18 days followed each flight. Examination of the data reveals that all crew members lost mass in flight, and that this loss did not result in a net increase in density. Elevated urinary and blood nitrogen, a net negative calcium and nitrogen balance and a decrease in the radiographic density of certain bones support the conclusion that lean body mass decreased. That the loss was primarily proteinaceous in nature is evidenced by the comparatively small net change in total body water and by a decrease in total body potassium each measured by isotopic dilution techniques. These changes in body composition, despite a constant caloric intake in flight and on the ground, suggest that the body's demand for exogenous nutrient energy is not measurably changed by exposure to null gravity flight up to 84 days in duration.