Influence of Subcutaneous Fat Thickness upon the Activation Volume in Transcutaneous Electrical Stimulation to a Thigh Simulation Model

Activation Volume, which is calculated from the Activating Function, describes the spatial location of nerve activation, thus is useful in optimizing stimulation electrodes geometry and waveform for improving selectivity and comfort in transcutaneous electrical stimulation. For example, the discomfort due to the fat thickness has been studied before, but the effect of fat thickness on selectivity, which could be studied through the Activation Volume, needs to be further analyzed. In this study, we implemented a human thigh model using the Finite Element Method to study the effect of fat thickness on the Activation Volume in terms of penetration and volume. The thigh model was represented by a multiple layer cylinder composed of superficial stimulation electrodes, skin, subcutaneous fat, muscle, and bone. We found out that the selectivity under the electrode is better for smaller fibers close to the electrode, because the activation volume for those fibers do not spread out the area under the electrode.