The effect of subcutaneous fat thickness on the efficacy of transcutaneous electrical stimulation

Transcutaneous electrical stimulation is a widely used technique to relieve the symptoms of various neuromuscular disorders and to improve muscle strength. It is currently being investigated in the treatment of obesity to physically enable and encourage increased levels of voluntary exercise. Due to the high resistivity of subcutaneous fat tissue, higher stimulus currents are required to evoke muscle contraction in obese subjects than in subjects of a healthy weight, which can lead to patient discomfort. In this study, a three-dimensional finite element model of the human thigh, including skin, fat, muscle and bone, was developed to examine the relationship between fat thickness and evoked muscle activation. The effects of fat thickness, electrode size and inter-electrode distance on the activating function were investigated during monopolar and bipolar stimulation. The amplitude of the activating function was found to reduce as electrode size increased, however, this effect was relatively less at higher fat thicknesses. The activating function was also less sensitive to inter-electrode distance as fat thickness increased. These results indicate that by increasing electrode size, the current density at the skin surface can be reduced, thereby reducing patient discomfort while maintaining the efficacy of the electrical stimulation in obese patient populations.