Experimental set-up and electrode position. The active electrode (A) was placed over the motor point of the ECRB muscle. The passive electrode was placed over the radial styloid process (B). The common reference electrode was placed on the dorsum of the hand (C). A concentric needle electrode (D) was inserted in a distal to proximal direction parallel to the muscle fibers so that the tip of the needle was underneath the active electrode (A).