Light electric vehicles are a viable way of reducing urban congestion and local pollutant emissions. However, differently from more classical hybrid electric vehicles, the energy management of hybrid bicycles has been very little investigated in the literature. In this work the problem is tackled using optimal control principles, for an innovative series hybrid prototype in which there is no direct mechanical link between the pedals and the wheel. The problem is formulated as the minimization of the perceived exertion while constraining the state of charge of the battery. An approximated solution of the problem suited for online implementation is also presented and tested in a realistic simulation scenario.