title: The relationship between dietary intake, exercise, energy balance and the space craft environment.
abstract: Space flight is associated with the loss of skeletal muscle, principally from muscles with anti-gravity functions. Examination of data across different missions can permit a distinction to be made between true microgravity responses and what are mission-specific responses. Protein metabolism has been investigated on six missions, four short-term [Shuttle missions Space Life Sciences 1 (1991, SLSI), Space Life Sciences 2 (1993, SLS2), Deutsche-2 (1993, D2) and the Life and Microgravity Sciences (1996, LMS)] and two long-term missions (Skylab 1993 and NASA/MIR, 1996-1998). Measurements made include dietary intake (six missions), nitrogen balance (four missions), whole-body protein kinetics with [15N]glycine as the tracer (four missions) and cortisol excretion (three missions). Also available for comparison are bed rest studies with and without exercise. The purpose of this paper is to see what can be learnt about the muscle loss problem by comparing metabolic results across the six missions for which data are available and against bed rest. The analysis suggests that there is a linkage between the inability to maintain energy balance and exercise, and the connection is the decreased efficiency of removal of the metabolic by-products of exercise (heat, CO2) during space flight.
authors.affiliation: Department of Surgery, University of Medicine and Dentistry of New Jersey-SOM, Stratford 08084, USA. tpstein@umdnj.edu
authors.forename: T P
authors.initials: TP
authors.lastname: Stein
mesh_terms: D001510:Bed Rest; D001833:Body Temperature Regulation / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism; D004435:Eating / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D004777:Environment; D015444:Exercise / Q000502:physiology*; D005998:Glycine / Q000493:pharmacokinetics; D006801:Humans; D009124:Muscle Proteins / Q000096:biosynthesis; D018482:Muscle, Skeletal / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D009587:Nitrogen Isotopes; D013026:Space Flight
chemical_list: D009124:Muscle Proteins; D009587:Nitrogen Isotopes; D002245:Carbon Dioxide; D009584:Nitrogen; D005998:Glycine