It is expected that Body Area Networks will be deployed in various applications to instrument and support humans in many aspects of their life. Different standards actually compete to fulfil the constraints associated with possible applications. Among all possible applications, we focus in this work on multi-nodes monitoring applications. The body is thus equipped with a set of sensors transmitting in real-time their measures to a common sink. The underlying network topology is thus classical in the field of wireless sensor networks (WSN) and referred to as the star topology. The classical super-frame structure as proposed in 802.15.3 seems to comply with the needs of such an application. However, the specificities of the BAN channel can reduce the performance of such protocol. Indeed, the channel time variations make the star structure unstable and subject to a high level of packet loss. We propose to investigate some cooperative mechanisms to address this problem and we evaluate their implementation in the superframe structure. The paper is organized as follows. The scenario, application constraints and super-frame structure are described in section I. Section II depicts the most important radio channel properties which impact this kind of scenario (time varying radio channel). Section III reviews some cooperative mechanisms and in section IV, these mechanisms are integrated in the super-frame structure. Section V, simulation results are provided.