Background and aim: Exercise activities increase bone mass, however, the effect of  detraining and inactivity on osteoporosis in active people who take part in regular physical activity, are still not well understood. The purpose of this study was to investigate the effect of treadmill running exercise together with detraining on osteoporosis in Oophorectomized rats.

Methods: Fifty female rats divided randomly into control experimental 1 (oophorectomized rats for 12 weeks) experimental 2 (oophorectomized rats for 22 weeks) experimental 3 (oophorectomized rats undergoing treadmill running exercise) and experimental 4 (oophorectomized rats undergoing treadmill running exercise together with a period of detraining) groups. Control group sacrificed in the beginning of the study. The experimental groups of 3 and 4 exercised for 10 weeks. After the training period, The experimental groups of 1 and 3 were sacrificed, while, experimental groups 4 and 2 remained detraining. The exercise program consisted of running on a treadmill (3 days/week for 10 weeks). The speed of treadmill was adjusted constant at 12 m/min and the duration of exercise began from 10 min in the first week and reached up to 64 min in the 10^th week of exercise. At the end of study, all rats were sacrificed and their femurs were removed for bone micro structures (cortical and trabecular thickness, and trabecular separation) and bone strength analysis. We used One-Way ANOVA and  post hoc Scheffe test to compare the groups after evaluation of Homology of variances by Shapiro wilk test. P&le 0.05 considered significant.

Results: Trabecular thickness decreased significantly in experimental groups of 1 and 2 compared with control group (P<0.05). Bone strength and cortical thicknesses decreased significantly in experimental groups of 2 compared with control group (P<0.01). Bone strength and femoral micro structures improved in experimental group of 3 compared with experimental group of 1 and in experimental group of 4 compared with experimental group of 2 (P<0.001). cortical thickness decreased significantly in experimental group of 4 compared with experimental group of 3 (P<0.025). 

Conclusion: Moderate intensity treadmill running exercise has a prophylactic effects on osteoporosis which remain after detraining. Prevention of osteoporosis leads to reduce of pathological fractures.