High voltage stimulation. Effects of electrode size on basic excitatory responses

The purpose of this study was to examine the effects of electrode size on thresholds of sensory and motor excitation, strongest motor excitation without pain perception, and strongest motor excitation coupled with maximally tolerated painful stimulation. A high voltage stimulator with monophasic pulsatile current was applied to the quadriceps femoris muscles of 14 healthy subjects. Voltage output, pulse-charge density, and isometric muscle torque were measured during random application of four electrode pairs measuring 3 X 3, 6 X 6, 9 X 9, and 5 X 16.2 cm. Results indicated a dependence of the measured variables on electrode size; the larger electrodes required greater voltage output but less pulse-charge density than the smaller electrodes. The two largest electrodes evoked significantly greater non-painful and maximally tolerated painful muscle torques. Maximal volitional contraction increased 13.3% after completion of all stimulations. Electrode size should be considered by physical therapists when administering transcutaneous electrical nerve stimulation.