The purpose of this study was to investigate whether partial weight-bearing activity, at either one-sixth or one-third of body mass, blunts the deleterious effects of simulated microgravity (0G) after 21 d on muscle mass and quantitative/qualitative measures of bone.
Using a novel, previously validated partial weight-bearing suspension device, mice were subjected to 16% (G/3, i.e., simulated lunar gravity) or 33% (G/6, i.e., simulated Martian gravity) weight bearing for 21 d. One gravity control (1G, i.e., Earth gravity) and tail-suspended mice (0G, i.e., simulated microgravity) served as controls to compare the effects of simulated lunar and Martian gravity to both Earth and microgravity.
Simulated microgravity (0G) resulted in an 8% reduction in body mass and a 28% lower total plantarflexor muscle mass (for both, P < 0.01) as compared with 1G controls, but one-sixth and one-third partial weight-bearing activity attenuated losses. Relative to 1G controls, trabecular bone volume fraction (−9% to −13%) and trabecular thickness (−10% to −14%) were significantly lower in all groups (P < 0.01). In addition, cancellous and cortical bone formation rates (BFR) were lower in all reduced weight-bearing groups compared with 1G controls (−46% to −57%, trabecular BFR; −73% to −85%, cortical BFR; P < 0.001). Animals experiencing one-third but not one-sixth weight bearing exhibited attenuated deficits in femoral neck mechanical strength associated with 0G.
These results suggest that partial weight bearing (up to 33% of body mass) is not sufficient to protect against bone loss observed with simulated 0 g but does mitigate reductions in soleus mass in skeletally mature female mice.
1Department of Health and Kinesiology, Texas A&M University, College Station, TX; 2Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN; 3Department of Biomedical Engineering, Texas A&M University, College Station, TX; 4Department of Mechanical Engineering, Texas A&M University, College Station, TX; and 5Department of Nutrition and Food Science, Texas A&M University, College Station, TX
Address for correspondence: Susan A. Bloomfield, Ph.D., Department of Health and Kinesiology, MS 4243, Texas A&M University, College Station, TX 77843-4243; E-mail: firstname.lastname@example.org.
*J.M.S. and F.L. contributed equally to this article.
Submitted for publication December 2012.
Accepted for publication April 2013.