Effects of tower climbing exercise on bone mass, strength, and turnover in growing rats

To determine the effects of tower climbing exercise on mass, strength, and local turnover of bone, 50 Sprague-Dawley rats, 10 weeks of age, were assigned to five groups: a baseline control and two groups of sedentary and exercise rats. Rats voluntarily climbed the 200-cm tower to drink water from the bottle set at the top of it. In 4 weeks, the trabecular bone formation rate (BFR/bone surface [BS]), bone volume (BV/TV), and trabecular thickness (Tb.Th) of both the lumbar vertebra and tibia and the bone mineral density (BMD) of the tibia increased, while the osteoclast surface (Oc.S) decreased. The parameter values in the midfemur, such as the total cross-sectional area, the moment of inertia, the periosteal mineralizing surface (MS/BS), mineral apposition rate (MAR), BFR/BS, and bending load increased, while the endosteal MAR decreased. In 8 weeks, the increases in the bone mineral content (BMC), BMD of the femur and tibia, and the bending load values of the femur were significant, but the climbing exercise did not increase BMC, BMD, or the compression load of the lumbar vertebra. Although the periosteal MS/BS, MAR, and BFR/BS increased, the endosteal MS/BS, MAR, and BFR/BS decreased. These results show that climbing exercise has a beneficial effect on the femoral cortex and tibia trabecular, rather than the vertebral trabecular. In the midfemur, effects on bone formation are site specific, supporting accelerated cortical drift by mechanical stimulation.