Evaluation of total muscular activity by quantification of electromyograms through a summing amplifier

In the present investigation a method of quantifying electromyograms (EMG's) from different muscle groups of the body to evaluate total muscular activity is described. A unipolar pickup, i.e., one standard silver cup surface electrode over each active muscle, was used because the EMG outputs with this electrode configuration during the same muscular activity were found to be greater than those with a bipolar pickup, i.e., two electrodes over each muscle. It was observed that for the purpose of quantification the root mean square (r.m.s.) value of a ‘steady’ level or the average r.m.s. value of a varying level of EMG is related in a linear fashion to the absolute mean value of the wave obtained by integrating the EMG for a specified time interval after making the waveform unidirectional. A similar relationship was observed with different voltage levels from a noise generator which was used for calibration purposes. EMG's from different muscle groups during isometric as well as isotonic voluntary contractions were found to summate together outside the body in a manner similar to noise voltages, i.e., the r.m.s. value of the combined voltages is equal to the square root of the sum of the mean square values of the individual waves. A method of passing EMG's through a summing amplifier and then quantifying the output for the evaluation of total muscular activity was developed, which greatly reduces the system components normally necessary for such studies. The results obtained from a series of experiments are discussed in detail.