Measurement of electrical and contractile properties of motor units using EMG and accelerometry

We present a novel method for recording the electrical and contractile properties of a number of motor units using surface electromyography (EMG) and accelerometry. Preliminary results have been obtained for the left and right thenar muscles of three healthy male subjects. The motor units are recruited by stimulating the median nerve at the wrist using surface electrodes and graded stimulus amplitudes. The resulting M-waves and acceleration signals are decomposed into individual motor unit action potentials and twitches using a pattern recognition technique. Typically 15 to 20 motor units can be studied for each recording sequence.