Influence of Sex and Age on EMG Contraction Pattern

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Abstract
A study was made of the influence of sex and age on the EMG contraction pattern. Constant isometric contractions were executed with the adductor pollicis muscle for 60 sec under standardized conditions. The EMG was derived from this muscle with surface electrodes and with intramuscular needle electrodes, then converted analoge to digital and analysed with the aid of a PDP 8/I computer. Values measured were the integrated amplitude, peak-to-peak amplitude, and peak number. In order to produce a given tension, women as a rule required a higher amplitude and a larger peak number in the EMG than men. These differences are virtually absent when a contraction of half the maximum strength is requested. The comparability of results is therefore enhanced by examining subjects at contractions expressed in percentages of maximum strength. These differences between men and women suggest that women activate more motor units to produce the same contraction. An explanation of this phenomenon is yet to be found. The slight decrease in amplitude and peak number which occurs with increasing age, is usually not significant but nevertheless not to be neglected. On one hand, it can be explained by an increase in duration of action potentials and, on the other hand, by muscle fiber atrophy.

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