There has been increasing research on wireless body area networks (WBANs) due to their wide range of applications, rapidly developing personal equipment and healthcare support devices. This paper investigates a WBAN model that consists of many sensors. The sensors are distributed around the body and communicate with access points (APs). In order to improve the throughput of the system, an algorithm is applied to select the AP that has the best channel conditions to receive information from every sensor. Moreover, the authors developed the max–min power control algorithm to control the transmit power of sensors in the uplink and APs in the downlink depending on their channel condition. The proposed algorithm is investigated based on several parameters, such as the number of sensors, the number of APs, the length of uplink and downlink training in samples, and so on. According to simulation results, the sensor with max–min power control achieves higher throughput in all considered scenarios, leading to a significant improvement in the WBAN system throughput for both cases of the uplink and downlink.