A Duanshi PT98-type treadmill (Xin Ruan Information Technology Ltd., Shanghai, China) was used in this experiment.
Animals were trained according to the Bedford animal training load standard described in Table 1 and Fig. 1. After
1 week of adaptation training, rats were exercising twice a day,one time in the morning and one time in the afternoon with minimum 5 h rest between the two exercise segments. Total of 9 weeks exercise with each training cycle lasted for 1 week (6days exercise, 1 day rest). Vaginal smear was performed daily to monitor menstrual cycle for each rat throughout the 9-week study.Menstrual cycle dysfunction was diagnosed by the onset of estrus phase or length change of anestrus phase in
menstrual cycle as described previously.