Induced Cortical Drift and Increased Bone Formation by Resistance Exercise Training in Growing Male Rats = Induced Cortical Drift and Increased Bone Formation by Resistance Exercise Training in Growing Male Rats

다국어 초록 (Multilingual Abstract)

Effects of strenuous resistance exercise training on hindlimb bone formation and resorption were studied in growing male rats. Fifty-three Sprague-Dawley rats, 5 weeks of age, were assigned to control and training groups. Resistance training consisted of squatting at 75% of one repetition maximum for 150 squat/day and 3 days/week for 8 weeks. Animals were sacrificed at 0 (start), 4, and 8 weeks of the training period. Bone mineral value was measured in the femur middiaphysis and the tibia proximal metaphysis by DXA(Dual energy X-ray absorptiometry). Using histomorphometric analysis, bone mass, structure and bone cellular parameters were estimated in secondary spongiosa of the tibial metaphysis and in periosteal and endocortical site of midfemur. As compared with the age-matched control group, significant increases in bone mineral content (BMC) and bone mineral density (BMD) in femur and tibia were apparent after 4 weeks of resistance training. In tibial proximal metaphysis, bone formation rate/bone volume (BFR/BV) significantly increased after 4 weeks of resistance training but the number of osteoclast number/bone surface (Oc.N/BS) and osteoclast surface/bone surface (Oc.S/BS) was significantly decreased. In femoral middiaphysis, endocortical mineral apposition rate (MAR) significantly decreased after 4 weeks of resistance training, leading to an enlargement of bone marrow area. On the contrary, periosteal MAR and BFR/BV were increased, resulting in increased cross-sectional and cortical bone area. In conclusion, resistance training in young growing rats (1) increased bone formation and decreased bone resorption in the tibial metaphysis, and (2) enhanced the exercise-induced cortical modeling drift in midfemur.