Intermittent acceleration as a countermeasure to soleus muscle atrophy

The centrifuge proposed for the Space Station will most likely be used, in part, for countermeasure studies. At present, there is a paucity of information concerning the duration and frequency of acceleration necessary to counteract the atrophy process associated with microgravity. The present study was designed to investigate intermittent acceleration during non-weight bearing of the soleus muscle and its resultant effects on muscular atrophy. Each day rats were removed from hindlimbs suspension and accelerated to 1.2 g for four 15-min periods evenly spaced over a 12-h interval. The soleus muscle experienced non-weight bearing the remaining 23 h each day. This paradigm, when repeated for 7 days, did not completely maintain the mass of soleus muscle, which was 84% of control. Interestingly, the identical protocol utilizing ground support in lieu of acceleration successfully maintained the soleus muscle mass. The failure of the centrifugation protocol to adequately maintain soleus muscle mass might be due to an undefined stress placed on the animals inherent in centrifugation itself. This stress may also explain the transient decline in food intake of the intermittent acceleration group on the 2nd and 3rd days of treatment. Also, these data support the concept that the frequency of exposure, as opposed to the duration of exposure, to weight bearing during hindlimb unweighting seems to be the more important determinant of maintaining postural muscle mass.