Body Sensor Networks (BSNs) form a promising technology to supply healthcare to an ageing population. A large number of sensor devices, radios and MAC protocols are being developed. However, current solutions all assume a single-hop topology, while research results confirm the need for multi-hop topologies. In these multi-hop networks, because of the small scale of a BSN, node mobility will arise frequently. This work presents the first algorithm to support such Mobile BSNs, while remaining energy efficient.