Wireless body area networks (WBAN) consist of wireless smart sensor nodes placed on, in or around the human body for medical monitoring systems, entertainment and ubiquitous computing. The nodes in WBAN are usually battery-powered and they send sensed data from a human body, including heart rate, temperature and ECG, etc. to the medical centre to monitor the health situation of individuals. One of the major problems of a WBAN is to prolong the sensor network lifetime. To solve this major problem, different approaches are used, but the most effective one is a well-designed MAC protocol. This paper investigates three inter-BAN communication methods and suggests a coordinator node rotating mechanism to ensure energy balance among the sensor nodes and to extend the network lifetime up to 59%.