The electromyographic fatigue threshold is not a valid tool to assess muscle function

The present study aimed at determining the electromyographic fatigue threshold (EMG) from the EMG activity level and the EMG frequency content of the First Dorsal Interosseous. Thirty-seven healthy subjects performed seven isometric index abductions at randomly ordered percentages of maximal voluntary contraction (i.e., 20%, 25%, 30%, 35%, 40%, 50% and 60%). During these bouts, surface EMG was measured using a linear electrodes array (i.e., seven EMG channels) in the First Dorsal Interosseous. For each subject the EMG was determined from both Root Mean Square (RMS) and Mean Power Frequency (MPF) values, only if the following criteria were met: (i) significant positive linear regression (