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 rst network-MAC cross-layer broadcast protocol in WBAN. Our protocol, evaluated in the OMNET++ simulator enriched with realistic human body mobility models and channel models issued from the recent research on biomedical and health informatics, outperforms existing at broadcast strategies in terms of percentage of covered nodes, energy consumption and correct reception of causally-ordered packets (i.e. packets are received in the same order as they were sent by the sink). Furthermore, we investigate the resilience of both existing at broadcast strategies and our new protocol face to various transmission rates and human body mobility. Existing at broadcast strategies without exception start to have a drastic drop of performances for transmission rates above 11Kb/s while our cross-layer protocol performances maintains its good performances for transmission rates up to 190Kb/s.