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Energy efficient MAC protocols have been developed for wireless sensor and ad hoc networks so that inactive nodes can transition into sleep state to conserve energy. It has been recognized that maintaining a continuously awake Connected Dominating Set (CDS) serves to reduce the route setup latency. Under the Mobile Back-bone Network (MBN) architecture introduced by I. Rubin et al., a mobile backbone (Bnet) is dynamically constructed to provide a topological covering of the network. When the formed Bnet is unable to provide full covering of all nodes, nodes may have to use a multihop path to access the Bnet. In this case, the MBN employs a hybrid routing algorithm under which flows that travel a distance longer than a threshold level are directed along routes that travel across the Bnet. In turn, a limited span global route discovery process is applied for routing shorter distance flows. In this paper, we introduce and analyze an MBN based power saving protocol (MBN-PS) that employs this hybrid routing scheme. Under the MBN-PS scheme, dynamically elected backbone nodes are kept awake, while inactive non-backbone nodes can reside in sleep state, waking up periodically to receive wakeup notifications from other nodes. We present a model for the mathematic calculation of the bit-per-joule performance of the network as a function of the selected distance threshold levels. Using our method, a network designer is able to choose the optimal distance threshold level to be used by this scheme based on the underlying traffic loading conditions. We demonstrate the hybrid routing scheme to achieve high bit-per-joule performance when backbone nodes possess more energy resources than the non-backbone nodes.