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 mode of motor unit activities. This model is described as follows : (1) Mass EMG is the sum of all active motor units action potential trains. (2) An input of each motor unit is a statistically independent random pulse train. (3) Motor units are devided into groups by their threshold force for recruitment. Nj denotes the number of motor units belonging to group j, Kj denotes the size, and fj (Pi) denotes the firing rate. (4) The firing rate fj (Pi) is the function of force. By using the theory of the shot noise, the number Nj and the size Kj 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 fj (Pi). This estimation starts from the lowest threshold force group, using m2, m4, and fj (Pi). This method has been applied to the human brachialis muscle and the human extensor digitrum 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 comfirms 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.
|Number of pages
|Japanese journal of medical electronics and biological engineering
|Published - 1981
ASJC Scopus subject areas
- Biomedical Engineering