Wearable computing technologies are becoming widely used in healthcare and for tracking various human work and leisure activities. The collection and transmission of sensor data are fundamental functions of these technologies. A wireless body area network (WBAN) helps these wearable devices to continuously acquire ambulatory and physiological signals in real time with multiple sensor nodes attached or implanted into a human body. Sensor nodes transmit data to a sink node with wireless connections can enable mobility of human bodies. Since the data transmission rate of each sensor node is different, we proposed a variable-rate transmission MAC protocol (VTMAC) with coordinator election based on the time division multiple access method. This adaptive coordinator election scheme can balance the sensor nodes’ power consumption to extend the lifetime of WBAN as possible. It can also flexibly allocate time slots for each sensor node according to their different data transmission rates to enhance the efficiency of networks. The proposed method has been implemented and demonstrated on a hardware wireless communication platform with multiple wearable sensor nodes. Simulations show the VTMAC can achieve less power consumption and higher throughput performance compared with conventional protocols especially in high data transmission rate situation for the body area networks we simulated.