Effect of Orientation on Human Posture in Neutral Buoyancy and Parabolic Flight 2001-01-2149

Neutral buoyancy (NB) and parabolic flight (PF) are the only presently available human-scale three-dimensional spaceflight simulation environments, and as such, both NB and PF are used extensively to simulate spaceflight conditions for both research and mission operations purposes. However, there is little or no quantitative (or even qualitative) material in the literature to characterize the fidelity of either environment to its 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; tilted 90° Front, 90° Back, 90° Right, and 90° Left. PF limitations on test time and physical volume prohibited 90° testing; consequently the PF test protocol included only the Upright and 45° orientations. All NB testing was performed at the bottom of a 25’ deep NB facility, using SCUBA certified, experienced test personnel. All 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. ANOVA (analysis of variance) calculations were performed for individual and group comparisons. All subjects completed all trials for NB; however, some trials were lost during PF, due to subject motion sickness. Nonetheless, statistically significant differences (p<.05) between orientations for each environment (e.g., PF 45F v. 45B) were present, in agreement with previous orientation results. Differences were also found between environments (NB v. PF), indicating that results from one are not necessarily applicable to the other.