Exercise prevention of unloading-induced bone and muscle loss in adult mice

Skeletal unloading causes bone and muscle loss that may be reversed by post-unloading exercise. This study examines the effects of unloading and exercise, using tail-suspension for 14 days combined with a week of post-suspension cage wheel running in mice. Twenty-four adult, male, C57BL/6J mice were divided into four groups (n = 6 mice/group); unsuspended non-running, tail-suspended non-running, unsuspended running, and tail-suspended running. At sacrifice, the calf (soleus, gastrocnemeius and plantaris complex), heart, tibia and femur were collected and weighed. The femora and tibiae were cleaned of non-osseous tissue, subjected to 3-point bending (femurs only), and weighed for dry (105 degrees C; 24h) and ash mass (800 degrees C; 24h). The mean calf mass from the tail-suspended groups (157.13 +/- 2.83 mg) was significantly less than in the unsuspended groups (167.33 +/- 2.83 mg; p = 0.019), with no significant effect of cage wheel running. The mean heart mass in running groups (166.58 +/- 4.78 mg) was significantly greater than the non-running groups (148.17 +/- 4.78 mg; p = 0.013), with no effect of hindlimb suspension. The mean femur ash mass from tail-suspended groups (24.02 +/- 0.38 mg) were significantly less than the unsuspended groups (25.11 +/- 0.34 mg; p = 0.050), and the running groups (25.13 +/- 0.38 mg) were significantly greater than the non-running groups (24.00 +/- 0.34 mg; p = 0.043). No effect was observed for the femur dry mass or percent mineralization. Measurements of mechanical length tended to be lower in tail-suspension, with no significant affects do to cage wheel running. This study suggests that tail-suspension in adult mice significantly decreases skeletal muscle and bone mass, with no change in percent mineralization. Furthermore, one week of running does not reverse the effects on the skeletal muscle and bone mass.