Low-intensity, High-frequency Vibration Appears to Prevent the Decrease in Strength of the Femur and Tibia Associated with Ovariectomy of Adult Rats

The effect of low-intensity, high-frequency vibration on bone mass, bone strength, and skeletal muscle mass was studied in an adult ovariectomized (OVX) rat model. One-year-old female rats were allocated randomly to the following groups: start control, sham OVX, OVX without vibration, OVX with vibration at 17 Hz (0.5g), OVX with vibration at 30 Hz (1.5g), OVX with vibration at 45 Hz (3.0g). Vibrations were given 30 min/day for 90 days. During vibration each group of rats was placed in a box on top of the vibration motor. The amplitude of the vibration motor was 1.0 mm. The animals were labeled with calcein at day 63 and with tetracycline at day 84. The tibia middiaphysis was studied by mechanical testing and dynamic histomorphometry and the femur distal metaphysis by mechanical compression. OVX without vibration increased the periosteal bone formation rate and increased the medullary cross-sectional area, i.e., increased the endocortical resorption and outward anteromedial and lateral drifts of cortical bone at the tibia middiaphysis. OVX also resulted in a reduced maximum bending stress of the tibia diaphysis and a reduced compressive stress of the femur distal metaphysis. Vibration at the highest intensity, i.e., 45 Hz, of OVX rats induced a further increase in periosteal bone formation rate and inhibited the endocortical resorption seen in OVX rats. Furthermore, vibration at 45 Hz inhibited the decline in maximum bending stress and compressive stress induced by OVX. Neither OVX nor OVX with vibration influenced skeletal muscle mass. In conclusion, the results support the idea of a possible beneficial effect of passive physical loading on the preservation of bone in OVX animals.