The wireless local area network (WLAN) technology represents a well-established solution for short-range wireless connection to the Internet. However, its performance is limited by the use of an energy-consuming medium access control (MAC) protocol. Aiming to increase energy efficiency, this paper introduces an improved MAC protocol for infrastructure WLAN, incorporating a novel approach of bidirectional transmissions in the point (PCF) and distributed (DCF) coordination functions of the WLAN MAC standard. Based on this new concept, an access point and a station might exploit each successful established connection to convey bidirectional data. The enhanced MAC solutions are then evaluated through extensive simulations. The results of this work prove the feasibility of the MAC improvements to increase the energy efficiency in terms of Joule per bit, as well as throughput and bandwidth utilization, when compared with the legacy scheme.