Based on recent evidences, female athletes with ammenorhoe accompany low bone mineral density (BMD) at a high incident rate. In this study, we investigated the effects of running loading (R) and/or ovariectomy (OVEX) on BMD in the rat. SD rats (5W old) were divided into four groups and subjected to ;
　1 ) sham opration alone (SHAM-N ; no-running), 2 ) SHAM followed by running loading (SHAM-R), 3 ) OVEX without running (OVEX-N), and 4 ) OVEX with running loading (OVEX-R). Running loading was performed with a motor-driven treadmill at speed of 18 m/min for 1h everyday for 3 months. At the end of the experiment, rats were sacrificed, and the BMD in the femur and the spine were measured by DEXA. In SHAM groups, running loading significantly increased BMD of either the femur or the spine. This trend was similar in both cortical and cancellous sites of the femur. In contrast, OVEX resulted in a significant decrease in BMD of the spine. However, there was no effects on BMD in the femur. Moreover, running loading in OVEX rat decreased BMD of the femur, in either cortical or cancellous sites.
　The present data suggests that : 1 ) running loading (18 m/min for 1h) is effective to increase BMD in either the femur or the spine under normal hormonal state, and 2 ) low circulating estrogen state may induce a decrease in BMD of the spine and reverse the effects of running exrcise on BMD of the femur. Since female athletes with ammenorhoe usually have low BMD in the lower extremities, it is suggested that over-exercise under low estrogen appears to cause decreases in BMD and further induce the fatigue fracture.

DESCENTE SPORTS SCIENCE Vol.16/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE