Figure 4

Motor point identification procedure. Panel I: schematic representation of monopolar stimulation. The active electrode is placed over the muscle region of interest and the reference electrode is placed over the antagonist muscle or opposite to the active electrode to close the stimulation current loop. Panel II: electrophysiological procedure for motor point (MP) identification and proper electrode placement. The skin surface above the vastus lateralis muscle is mapped with a pen-electrode, the dispersive reference electrode being placed opposite to the active one; the joint angle should be the one adopted for the subsequent stimulation protocol in order to avoid skin displacement with respect to the underlying neural and muscular structures. A) The muscle contractile response is not evident when the pen is not facing the MP area. B) The MP of the target muscle is identified as the specific site where a minimal mechanical response is generated with the lowest current intensity. C) The identified MP is marked with a felt tip. D) The active electrode is placed exactly over the identified MP.