Schematic representation of the muscle and the electrode detection area. Upper circle indicates the electrode detection area, lower circle indicates the muscle and the subcutaneous layer. re: radius of electrode detection area (10 mm), rm: muscle radius (20 mm), d: thickness of the subcutaneous layer (2 mm). The ratio between the part of the muscle within the electrode detection area and total muscle cross-section area was calculated for estimation of the number of MUs that contribute to the EMG signal in relation to the total number of MUs, located throughout the muscle. Dotted lines indicate the triangle used for calculation of θ. Shaded area indicates the part of the electrode detection area that lies within the subcutaneous layer and does not contain MUs.