Subject Effects Exhibited in Human Posture in Neutral Buoyancy and Parabolic Flight

Abstract

Neutral buoyancy (NB) and parabolic flight (PF) are the only available human-scale three-dimensional spaceflight simulation environments. As such, both environments are used extensively for both research and mission operations purposes despite a lack of quantitative (or even qualitative) characterization of the fidelity of either environment to the spacelfight analog. The present study was undertaken as part of a larger research effort to begin to build such characterizations. Eight healthy adults (4 men and 4 women) were asked to adopt relaxed postures while 'standing' in space shuttle middeck standard-type foot restraints, in NB and during the 0g periods of PF. Subjects were tested in NB in 9 orientations, 3 trials each: Upright; tilted 45° Front, 45° Back, 45° Right, 45° Left; and tilted 90° Front, Back, Right, and Left. PF limitations prohibited 90° testing; consequently the PF test protocol included only Upright and 45° orientations. NB testing was performed at the bottom of a 25' deep NB facility, using SCUBA certified, experienced test personnel. PF testing was performed during four flights on the NASA KC-135. Subjects were fully informed of the test protocol prior to and during testing. Reaction loads were recorded for each foot independently and normalized to subjects' masses; hip, knee, and ankle angles were measured from photographs. Trunk and shank angles (defined respectively by hip-shoulder ray and ankle-knee ray angles to the foot restraint plane) were also recorded. All subjects completed all trials for NB; however, some trials were lost during PF, due to subject motion sickness. Nonetheless, statistically significant ANOVA (analysis of variance) outcomes (p<.05) were found between subjects for both postural angles and reaction loads, and also between test conditions for each subject. These results indicate that individual posture maintenance strategies vary in both environments, and do not represent a single consistent neutral posture model in either.