Effects of electrode size on basic excitatory responses and on selected stimulus parameters.

Recent data have implicated the size of surface electrodes as an important factor affecting peripheral nerve excitation. Therefore, we studied the effects ol electrode size on the basic excitatory responses and on stimulus characteristics. Four different sizes of self-adhesive surface electrodes were applied over the medial and lateral gastrocnemius muscle ol 20 healthy subjects. The excita- tory levels were sensory threshold, motor threshold, pain threshold, and maximally tolerated painful stimulation. Stimulus parameters included a symmetric biphasic waveform, 200 fisec phase duration, and a pulse repetition rate of 50 pps. Amplitude was increased until the appropriate excitatory response was achieved. At this amplitude level, the computerized recording system collected data of stimulus peak current, peak voltage, and phase charge as well as isometric plantar flexion force. Repeated measure analysis of variance and Newman-Keuls post hoc tests revealed that increasing electrode size significantly decreas...