Effects of endurance exercise on three-dimensional trabecular bone microarchitecture in young growing rats

Appropriate endurance exercise is capable of increasing bone mass and strength in both animals and humans. We examined the skeletal changes induced by treadmill running exercise in young growing rats with a particular emphasis on three-dimensional trabecular bone microarchitecture. Fourteen male Wistar rats were divided into sedentary (CON; n = 7) and exercised (RUN; n = 7) groups at the age of 4 weeks. The rats in the RUN group performed the treadmill running exercise of 30 m/min for 60 min, 5 times a week. After 10 weeks of exercise, bone mineral density (BMD), cortical geometry, diaphyseal breaking force, and trabecular bone microarchitecture in the femur were measured. Three-dimensional trabecular bone microarchitecture was evaluated at the distal femoral metaphysis using microcomputed tomography. The running exercise significantly increased BMD, bone volume, bone volume fraction, trabecular thickness, and trabecular number, whereas trabecular bone pattern factor, the parameter associated with decreased trabecular connectivity, was significantly lower in the RUN group than the CON group. On the other hand, no significant difference in the degree of anisotropy and structure model index was observed between the two groups. At the femoral diaphysis, running exercise significantly increased cortical bone area, width, and maximum load without affecting bending stress, implying that the material properties of bone had not changed in the exercised rats. These results suggest that the increase in bone strength induced by endurance exercise is mediated by changes in trabecular bone microarchitecture as well as density and cortical geometry.