1. Apparatus for actuating a skeletal muscle of a patient, comprising: a plurality of electrodes, which are adapted to be placed in a vicinity of a motor nerve that innervates the skeletal muscle; and a control unit, which is adapted to drive a current between two or more of the plurality of electrodes, and to configure the current such that a first subset of axons in the nerve is excited by the current and such that a second subset of axons in the nerve is not excited by the current.