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

Departments of ¹Aerospace Physiology and ²Aerospace Biodynamics, Fourth Military Medical University, Xi'an 710032, People's Republic of China

Submitted 21 October 2002 ; accepted in final form 26 February 2003

This study was designed to compare the effectiveness of daily short-duration -G_x 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 -G_x 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 -G_x gravitation by STD was sufficient to prevent adverse changes in myocardial contractility; bone is most resistant: 4 h/day of -G_x 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 -G_x 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.

rat; hindlimb unweighting; intermittent artificial gravity; countermeasure; myocardial contractility; skeletal muscle; atrophy; bone; osteopenia; centrifugation

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