Effectiveness of intermittent -Gx gravitation in preventing deconditioning due to simulated microgravity

This study was designed to compare the effectiveness of daily short-duration -Gx gravity exposure in preventing adverse changes in skeletal and cardiac muscles and bone due to simulated microgravity. Tail suspension for 28 days was used to simulate microgravity-induced deconditioning effects. Daily standing (STD) at 1 G for 1, 2, or 4 h/day or centrifugation (CEN) at 1.5 or 2.6 G for 1 h/day was used to provide -Gx gravitation as a countermeasure. The results indicate that the minimum gravity exposure requirements vary greatly in different systems. Cardiac muscle is most responsive to such treatment: 1 h/day of -Gx gravitation by STD was sufficient to prevent adverse changes in myocardial contractility; bone is most resistant: 4 h/day of -Gx gravitation only partially alleviated the adverse changes in physical and mechanical properties of the femur. The responsiveness of skeletal muscle is moderate: 4 h/day of -Gx gravitation prevented mass reduction and histomorphometric changes in the soleus muscle during a 28-day simulation period. Increasing gravitational intensity to 2.6 G showed less benefit or no additional benefit in preventing adverse changes in muscle and bone. The present work suggests that system specificity in responsiveness to intermittent gravity exposure should be considered one of the prerequisites in proposing intermittent artificial gravity as a potential countermeasure.