This study aimed at obtaining the quantitative information about the functional state of the muscle contraction from surface EMG by means of spectral analysis, and revealing the relationship between the surface EMG and the NMU activity. The usefulness of this method was also examined in relation to its application to the motor function disorders. For the quantitative measurement of surface EMG and NMU impulse activity, auto-and cross-spectral analysis was performed by a general purpose digital computer (MC-1).
The results were as follows;
1)
Changes of surface EMG due to the functional states of muscle contraction.In the normal subjects, strengthening of muscular contraction resulted in increase of higher frequency component of the spectra, and lower frequency component was dominant in the fatigued muscles. Coherence between two simultaneous EMG records from the same muscle tended to increase under the strong contraction or after the sustained contraction. In hemiparetic patients, the lower frequency component was dominant, and relatively lower value of coherence was obtained from the paretic muscles. In Parkinsonian patients, marked frequency shift of spectra to higher frequency and increase of coherence were observed during strengthening contraction, on the contrary, however, at the maximal contraction, the coherence was decreased.
2)
Relationship between the NMU discharges and surface EMG.In healthy subjects and Parkinsonian patients, lower coherence was obtained between the two EMG phenomena, when the dominant component of surface EMG was in higher frequency range (more than 30Hz). While the higher coherence, on the contrary, was detected, when lower component (10-20Hz) was dominant. In hemiparetic patients, paretic limb showed slightly lower coherence than normal side.
These results were discussed from the aspects of the mass activity of NMU, and the surface EMG was considered as a useful indicator to characterize the functional states of muscle activities. Thus, appropriate frequency analytical data processing of the surface EMG was expected to be an effective tool for obtaining informations of the normal and abnormal motor functions.
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