A critical benefit analysis of artificial gravity as a microgravity countermeasure

Abstract

Human physiological systems, especially the cardiovascular and musculo-skeletal systems, are well-known to decondition during spaceflight. Several countermeasures that are in use today have been rigorously developed over the decades to combat this deconditioning. However, these countermeasures are system specific and have proven to be only partially effective. Artificial gravity has been persistently discussed as a countermeasure that potentially has salutary effects on all physiological systems, though few ground-based studies have been performed in comparison to other countermeasures. The current analysis attempts to elucidate the effectiveness of artificial gravity by directly comparing results of previously published and unpublished deconditioning studies with those of more traditional, ground-based countermeasures (i.e. resistive exercise, aerobic exercise, lower body negative pressure, or some variation of these). Animal studies were also evaluated to supplement the knowledge base and to fill gaps in the human countermeasure literature. Designs of published studies, such as study duration, deconditioning paradigm, subject selection criteria, measurements taken, etc., were confounding variables; however, studies that had some measure of consistency between these variables were compared, although notable differences were cited in the analysis and discussion. Results indicate that for prolonged spaceflight an artificial gravity-based countermeasure may provide benefits equivalent to traditional countermeasures for the cardiovascular system. Too few comparable, human studies have been performed to draw any conclusions for the musculo-skeletal system, although animal studies show some positive results. Gaps in the current knowledge of artificial gravity are identified and guidance for future deconditioning studies is offered. Based on the results of this study, a comprehensive artificial gravity protocol is proposed and future research topics using this countermeasure are addressed.