The main reasons for weak legs during menstruation are the following: First, due to the decline of estrogen and progesterone in the body, the endometrium loses support therefore bleeding will occur, and if the bleeding is high it may lead to anemia and symptoms such as weak legs. Secondly, it is considered to be menstrual syndrome. Some women will have various symptoms such as emotional instability, appetite change, restlessness and weakness of legs during menstruation, which are normal physiological reactions. Thirdly, it is considered to be caused by excessive strain during menstruation, often sitting or standing for a long time or doing too heavy physical work, and other factors, which need to be promptly treated by the hospital. Fourthly, it may be caused by other systemic diseases or orthopedic diseases, while calcium deficiency or malnutrition cannot be completely excluded, it is best to actively check and treat.