Estimation from surface EMG of the distribution of motor unit sizes in the m. vastus lateralis

In this study, the sizes of motor units in the human vastus lateralis muscle were estimated using multichannel surface EMG. A comparison was made between the distributions of motor unit (MU) sizes obtained with the surface EMG technique and with the macro EMG needle technique. The ultimate goal is the development and validation of a method for the estimation of the distribution of motor unit sizes using only surface EMG. Macro EMG and surface EMG were measured simultaneously. The single fiber signal provided by the macro needle was used as a trigger signal for both the macro and the surface EMG signal. For 6 of the 8 measured subjects, a good similarity was found between the two MU size distributions using a single subject independent scaling factor. This scaling factor relates the area of the surface EMG MU potential (MUP) to the area of the macro EMG MUP and was found to be remarkably close to unity (1.03)