Intermittent gravity: How much, how often, how long?

摘要: Continuous exposure to gravity may not be necessary prevent the deconditioning effects of microgravity. It is known, however, what minimum (G) reguirements are, whether they vary for different physiological systems, or passive Gz (gravity in head-to-toe vector) activity a G field more effective preventing deconditioning. also known optimal characteristics stimulus should terms amplitude, duration, and frequency. To begin address these questions, 4-day -6 deg head-down bed rest (HDBR) study was conducted. Nine males (aged 30-50 yr) were subjected, over period seven months, four +1 protocols (periodic standing controlled walking each total 2 4 hr/day individual 15-min doses), plus control (0 Gz) continuous HDBR. The consisted one ambulatory day, full days HDBR, recovery day when subjects released at end HDBR after completion tests. A battery tests selected standardized order evaluate early responses Dependent variables interest included orthostatic tolerance (30 min 60 head-up tilt) hemodynamics during tilt, peak oxygen consumption (VO2(sub peak)) plasma volume (PV), urinary calcium (Ca). results as follows: hr completely prevented partially post-HDBR intolerance. Walking 3 mi/hr provided no additional benefit. Intermittent attenuated, but did prevent, decrease VO2(sub peak). Both conditions showed less PV loss by HDBR; both without effect. essentially Ca excretion than standing. concluded that systems benefit differentially from Gz, intensity an important contributing factor.