Estimation of the number of motor units by processing mass electromyogram

M. Yoshida, Kazuyuki Kanosue, K. Akazawa, K. Fujii

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A new method of estimating the number and the size of active motor units by processing mass electromyogram (EMG) has been devised. This method is based on a model of mass EMG generation, which is founded on the knowledge of the motor unit activities. This model is described as follows: (1) Mass EMG is the sum of all active motor unit action potential trains. (2) An input of each motor unit is a statistically independent random pulse train. (3) Motor units are divided into groups by their threshold force for recruitment. N(j) denotes the number of motor units belonging to group j, K(j) denotes the size, and f(j)(Pi) denotes the firing rate. (4) The firing rate f(j)(Pi) is a function of force. By using the theory of shot noise, the number N(j) and the size K(j) of motor units of each group are expressed as a function of the second and fourth moments of mass EMG (m2 and m4) and the firing rate f(j)(Pi). This estimation starts from the lowest threshold force group, using m2, m4, and f(j)(Pi). This method has been applied to the human brachialis muscle and the human extensor digitorum communis muscle. The estimated results agree with the size principle and the physiological knowledge of the relation between the threshold force and the number of motor units. This agreement confirms the propriety of this estimation method. The estimation accuracy, that is, the relation between the observed period of mass EMG, which means the integration time for the calculation of moments, and the deviation of estimated values, is elucidated theoretically.

Original languageEnglish
Pages (from-to)187-194
Number of pages8
JournalJapanese Journal of Medical Electronics and Biological Engineering
Issue number3
Publication statusPublished - 1981
Externally publishedYes


ASJC Scopus subject areas

  • Electrical and Electronic Engineering

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