well, it is all a great mystery. Aborigens make balls of dried menstrual blood to use them as a medicine. Also taoists think the menstrual blood is loaded with chi.
They found out that women athletes run faster during the cycle. A friend told me that in Israel army, when there was a very dangerous action, they chose women who eventually had their cycle (this could just be a fairy-tale, I don't know). For sure menstrual blood is loaded of magical power.