New technologies can help to develop preventive healthcare, thereby leading to significant life quality improvements. Medical Body Area Networks are expected to become a key element in tomorrow's medical IT infrastructure by enabling the long term collection and analysis of health parameters. For this vision to become a reality, several challenges must be addressed. This work focuses on the technological aspects of ultra low power consumption, low latency and packet error rate. We consider and evaluate state of the art technologies currently under evaluation by the IEEE Standard Association 802.15.6 task group on body area networks, using detailed network simulation models, which have been calibrated with hardware measurements whenever possible and with MATLAB communication link simulations otherwise. We observe that the expected power consumption levels are similar for all considered platforms, and that they are determined mainly by the medium access control protocol. Trade-offs between communications latency, throughput and power consumption are identified. The performance of the Ultra Wideband Impulse Radio system is clearly impacted by its lack of carrier sensing capability. We conclude that the existing technologies are mature enough and that the remaing obstacles to widespread adoption are organizational and societal.