EXTRACTION OF ACCELERATION SIGNALS RELATED TO MOTOR UNIT ACTION POTENTIALS

Abstract

A novel method is described for recording the electrical and contractile properties ^of a number ofhuman motor units using surface electromyography (EMG) and accelerometry. 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 acceleration responses using a pattern recognition technique. Results obtained for the left and right thenar muscles ofthree healthy male subjects are presented. For the six thenars, a minimum of9 and maximum of 17 MUs could be studied, resulting in a total sample of72 MUs. Using data from these subjects, a study ofthe relative efficacy ofvarious EMG pattern recognition strategies including those based on time, Fourier and wavelet analysis is also analyzed. The findings ofthe present study agree well with similar research using force measurement. It may be concluded that acceleration measurement can be used as an alternative to isometric twitch forces and may be more suitable because ofthe relative x ease ofinstrumentation and lack ofsubject discomfort. It also follows that a pattern 'recognition scheme based on MUAPs allows the measurement of contractile properties of many more MUs for each muscle studied than can be accomplished by other published techniques