To support reliable real-time applications in Body Sensor Networks (BSNs), it is necessary to develop an efficient and robust routing protocol. However, it is challenging due to the specific radio propagation characteristics, dynamic network topology, variable link quality caused by body movements or environments, extremely low transmission power and limited battery among many others. In this paper, we propose Reactive Virtual Coordinate Routing protocol (RVCR) to tackle the challenges in BSNs by making a good use of the specific radio propagation and link characteristics on the human body. The basic idea of RVCR is that it efficiently exploits the temporary high-quality link opportunities resulting from the body movements and the environments to effectively forward packets towards the destination. RVCR achieves a stable packet delivery ratio (PDR) of more than 99% independent of the body movements and the environments at the lowest possible transmission power. Besides high PDR, RVCR has a stable and small average number of hops per packet, which makes it energy efficient. Additionally, RVCR can keep the same performances even in case of severe link failures.