Whole-body vibration effects on bone before and after hind-limb unloading in rats

Introduction: Skeletal unloading during spaceflight leads to bone loss. Following long-duration flight, such loss may be very slow or impossible to fully recover. Therefore, it is important to seek countermeasures to prevent the loss. Methods: We studied the effects on bone of whole-body vibration (WBV) with variable parameters (10-60 Hz and 0.1-1 g) using hind-limb unloading (HLU) in the rat as a model for microgravity. The bone mineral densities (BMD) of the femur, tibia, and lumbar spines were measured and the mechanical properties of the femur were determined by mechanical testing. Serum alkaline phosphatase (ALP) and pyridinoline (PYD) levels were analyzed. Results: After 28 d of HLU, WBV reduced the losses of BMD in the femur and tibia from 18.8 to 10.1% and from 16.7 to 7.1%, respectively, and prevented the loss in stiffness of the femur after HLU. However, WBV had no effect on the lumbar spine. ALP levels were suppressed by HLU and maintained by WBV (28.3% increase). There was no significant difference in PYD among groups. In the recovery period following HLU, there were no significant effects of WBV on BMD, and the elastic modulus of the femur returned to normal. Discussion and Conclusions: Mechanical stimulation in the form of WBV limited reduction of bone density when it was applied during the unloading, but not afterward. It is of interest that the mechanical properties of the femur were influenced by WBV in the control femurs as well as in the unloaded bones of this rat model.