Power spectrum of electromyography in arm and leg muscles during isometric contractions and fatigue

Abstract

The electromyography of eight muscles were investigated in nine men to find out whether predominantly fast or slow muscles have different power spectral density function (PSDF). The PSDF was described as mean power frequency (MPF). The MPF in maximal isometric contractions was significantly lower in triceps brachii compared to biceps brachii or soleus, gastrocnemius and tibialis anterior. The quadriceps muscles did not differ from each other or from arm or shank muscles. During submaximal fatigueing contraction the shift of MPF to lower frequencies was evident in all the muscles investigated. Faster muscles (triceps brachii, biceps brachii) showed fast and radical decrease in MPF and the slower muscles (like soleus) followed the decreasing course later. The PSDF could be used as a noninvasive method for rough estimation of fast or slow fibre composition of a limb muscle.