Automatic digital analysis of the EMG during standardized flexion and extension of the foot

An analysis was made of parameters of the EMG contraction pattern of the soleus and the tibialis anterior muscle in normal test subjects. Constant isometric contractions were consecutively executed with both muscles during 60 sec under standardized conditions. The EMG was derived with surface electrodes, then converted analogue to digital and analyzed with the aid of a PDP 8/I computer. Values measured were tension, integrated amplitude, peak-to-peak amplitude and number of peaks. The fluctuations in tension exerted (coefficient of variation) were more marked in the tibialis anterior than in the soleus muscle. The difference between males and females in tension exerted was different for different muscles. The EMG pattern showed significant intermuscular differences, as did the fatigue phenomena. One of the causes is the ratio between tonic and phasic motor units. The same applies to intermuscular differences in fatiguability. Different muscles may dominant in different individuals. The above observations can explain the great range of variation in normal values. Comparative clinical studies will require a cataloguing of normal values for all muscles. This study can contribute to this.