Wireless Body Area Networks (WBAN) open an interdisciplinary area within Wireless Sensor Networks (WSN) research, with a tremendous impact in healthcare area where sensors are used to monitor, collect and transmit biological parameters of the human body. We propose the first network-MAC cross-layer broadcast protocol in WBAN. Our protocol, evaluated in the OMNET++ simulator enriched with a realistic human body mobility and channel model issued from a recent research on biomedical and health informatics, outperforms existing flat broadcast strategies in terms of network coverage, sensors energy consumption and correct reception of FIFO-ordered packets. We investigate the resilience of both existing flat broadcast strategies and our new cross-layer protocol face to various transmission rates and human body mobility. Existing flat broadcast strategies, without exception, start to have a drastic drop of performance for transmission rates above 11 Kb/s while our cross-layer protocol maintains its good performance for transmission rates up to 190 Kb/s.