KINESIOLOGICAL ELECTROMYOGRAPHY - Biomechanics and Motor Control of Human Movement - page 257

Figure 10.4 Variation in the amplitude and frequency content of the motor unit action
potential with increased electrode-motor unit distance. Predictions were for a small
motor unit (50 fibers) with 4 − mm 2 bipolar electrodes with an interelectrode spacing
of 11 mm. Shown are the m.u.a.p.'s at 1-, 10-, and 20-mm distances. (Reproduced by
permission from Biological Cybernetics , “Detection of Motor Unit Action Potentials
with Surface Electrodes: Influence of Electrode Size and Shaping,” A. F. Fuglevand, D.
A. Winter, A. E. Patla, and D. Stashuk, 67:143 - 153, 1992; Fig. 8. With kind permission
of Springer Science + Business Media.)

template matching, template updating, and motor unit firing statistics (De
Luca, 1993). As many as four motor units were detected and their firing rates
tracked from 0 to 100% of maximum voluntary contraction (MVC) of the
tibialis anterior muscle (Erim et al., 1996). It should be noted that only a frac-
tion of all active motor units can be tracked — only those within the pick-up
region of the electrode array. EMG recordings from surface electrodes have
been decomposed in order to determine the firing profile of those motor units
detected (McGill et al., 1987).

10.2 RECORDING OF THE ELECTROMYOGRAM

A biological amplifier of certain specifications is required for the record-
ing of the EMG, whether from surface or from indwelling electrodes. It is
valuable to discuss the reasons behind these specifications with respect to
considerable problems in getting a “clean” EMG signal. Such a signal is
the summation of m.u.a.ps and should be undistorted and free of noise or
artifacts. Undistorted means that the signal has been amplified linearly over
the range of the amplifier and recording system. The larger signals (up to
5 mV) have been amplified as much as the smaller signals (100 μ V and