Bone mass gained in response to external loading is preserved for several weeks following cessation of loading in 10 week C57BL/6J mice.

OBJECTIVE Dynamic loads lead to increases in bone mass. How long these gains are maintained after cessation of loading, however, is not fully understood. METHODS A long term study was performed in which skeletal changes were monitored by pQCT every 2-4 weeks (wks) for a 12 wk period after application of external loading using four-point bending device on 10 wk old female C57BL/6J mice. RESULTS 2 wks of loading caused 15-40% increase in bone parameters (vBMD, cross sectional area (CSA)) and bone strength (yield load, maximum load and toughness). Positive correlations between these two parameters (r= 0.72 to 0.88, p<0.05) suggest that the changes in bone parameters induced by loading are responsible, in part, for the increase in bone strength. Once loading is terminated the bone response did not continue. The vBMD gained by loading was significant for a period of 5 wks and returned to the levels of controls at 12 wks. The CSA though declined but was still significantly elevated at 12 wks. Bone strength showed no difference between loaded and non-loaded bones at 12 wks. CONCLUSION Our results show that external loading increased bone mass, was maintained for several weeks after termination of last loading.