Spectral analysis of the EMG signal is a useful tool for studying the complex phenomena of fatigue. The spectral parameters of mean frequency and median frequency, and the time domain parameter of root mean square have been used to measure localized fatigue.

The normal values of median frequency and its decline with fatigue have not as yet been determined in healthy subjects. This should be done in order to apply spectral analysis for clinical evaluations of abnormal populations. Normal median frequency values and its slope were established in this work for the upper extremity muscles of biceps, triceps and deltoid during a pilot study. The result showed that the triceps has a lower slope value, hence more type I fiber (fatigue resistant) as compared to that of biceps and deltoids. In addition, a monopolar fine wire electrode referenced to a surface electrode was compared with a bipolar surface electrode and bipolar fine wire electrodes in order to test the monopolar fine wire electrode as a technique to measure fatigue. The result showed that the monopolar fine wire electrode measured fatigue more reliably than the surface electrode, Further, for bipolar fine wire electrodes, where the active electrode is proximal to the motor point, the distance between the active electrode and the reference electrode is important in order to measure fatigue reliably.