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Energy expenditure during antiorthostatic bed rest (simulated microgravity)
R J Gretebeck1, D A Schoeller, E K Gibson
1Nutritional Biochemistry and Stable Isotope Laboratories, National Aeronautics and Space Administration, Johnson Space Center, Houston, Texas 77058, USA.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|June 1, 1995
Summary
Spaceflight simulations reduce total energy expenditure (TEE) mainly through decreased physical activity, not changes in basal or resting energy expenditure. Body weight doesn't reflect energy balance changes; increased body fat is observed.
Area of Science:
- Space physiology
- Human metabolism
- Nutritional science
Background:
- Limited research exists on energy balance and lean body mass during spaceflight simulations.
- Understanding these interactions is crucial for astronaut health and mission success.
Purpose of the Study:
- To investigate the relationship between energy balance and body composition in healthy men during simulated microgravity.
- To quantify changes in total energy expenditure (TEE) and its components.
Main Methods:
- Utilized doubly labeled water (DLW) to measure TEE in nine healthy men.
- Measurements were taken during a 7-day baseline period and a 10-day head-down bed rest (simulated microgravity) period.
Main Results:
- Mean TEE decreased by 21% during bed rest compared to baseline.
- Basal (BEE) and resting (REE) energy expenditures remained unchanged.
- Energy intake exceeded TEE, leading to a small but significant increase in body fat (0.44 kg).
Conclusions:
- Reduced TEE during simulated spaceflight is primarily due to decreased physical activity.
- Body weight changes are insufficient indicators of energy balance shifts during antiorthostatic bed rest.
- Increased adiposity suggests a need for closer monitoring of body composition over body weight alone.