Impact of chronic voluntary resistance training during recovery following hindlimb unloading on rat hindlimb muscles
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abstract
Little is known regarding the effects of multiple bouts of microgravity and 1g reloading on skeletal muscle, nor how the application of chronic resistance training during an initial recovery may affect muscle, either immediately or throughout a subsequent unloading. Male SpragueDawley (6mo) were assigned to the following nonexercise groups: 28d hindlimb unloading (HU), 28d HU session followed by a 56d recovery bout of normal cage ambulation at 1g (1HU+REC), 2 cycles of 28d HU with a 56d recovery period between unloadings (2HU), 2HU followed by an additional 56d recovery at 1g (2HU+REC), and an age and housingmatched control group (CON). Additionally, two groups of animals following the initial 28d HU session were given 7d recovery at 1g followed by a 7wk (3 sessions/wk) moderateintensity, moderatevolume voluntary resistance exercise program, in which the animals were trained to perform a controlled squatlike motion with full extension of the lower limb while under loads that gradually increased to additional resistances of ~65% bodyweight. Absolute muscle mass of the hindlimbs of the 1HU+REC/EX and 2HU+EX exercise groups did not differ significantly from their time and missionmatched counterparts (1HU+REC and 2HU, respectively), but relative mass does indicate a training effect in augmenting muscle recovery as well as a protective effect during an additional unloading exposure.
