Lower body negative pressure to provide load bearing in space

Results are presented from an experiment to determine whether lower body negative pressure (LBNP) produces a footward force equal to the product of the pressure differential and body cross-sectional area at the waist seal. Twelve male volunteers were sealed at the superior iliac crest in upright and supine LBNP chambers. Each subject was exposed to 10 mm Hg increments of LBNP up to 70 mm HG (standing) or to 50-100 mm Hg (supine), depending upon individual tolerance. Static reaction force was measured at each LBNP level for about 1-2 min. The forces measured during LBNP agreed well with forces calculated from the cross-sectional areas of the subjects' waists. It is inferred from these results that exercise in microgravity against 100 mm Hg LBNP could produce static and inertial forces similar in magnitude to those occurring on earth. It is concluded that this gravity-independent technique can help maintain the musculoskeletal and cardiovascular systems of crew members during prolonged exposure to microgravity.