  We analyze the performance of a Brownian ratchet in the presence of
geometrical constraints. A two-state model that describes the kinetics of
molecular motors is used to characterize the energetic cost when the motor
proceeds under confinement, in the presence of an external force. We show that
the presence of geometrical constraints has a strong effect on the performance
of the motor. In particular, we show that it is possible to enhance the ratchet
performance by a proper tuning of the parameters characterizing the
environment. These results open the possibility of engineering
entropically-optimized transport devices.
