A multi-layer finite element model of the surface EMG signal

The influence of skin, adipose tissue and bone on the rate of decay of the surface EMG signal around the limb was explored using a new finite element model. Replacing the outer layer of a homogeneous muscle model with a layer of highly resistive tissue, such as skin or fat, results in an increase In the surface potential. This also causes an increase in the rate of decay of EMG amplitude with increasing source depth and with increasing angular displacement from the source. EMG signals are examined as a bone is positioned at different locations throughout the muscle. Depending on its location, the highly resistive bone can significantly affect the amplitude of the surface potential. In a model of the upper arm, cross-talk around the limb was examined as subcutaneous tissue thickness was varied. EMG cross-talk was observed to increase with subcutaneous fat thickness. This is due to the relative increase in distance between source and recording site, rather than the material properties of the adipose tissue. The results illustrate the importance of including multiple tissue layers and inhomogeneities such as bone, when exploring aspects of surface EMG amplitude such as cross-talk.