Electromyographical assessment on muscular fatigue--an elaboration upon repetitive typing activity.

The objectives of this study were to quantify the electromyographic activities (EMG) of finger muscles during prolonged, low-forces, and repetitive typing with an ergonomically designed VDT workstation, as well as to analyze the occurrence and the possible mechanisms of muscular fatigue in touched typists. Thirty healthy female typists were recruited to type consecutively for 2 h. The surface EMG of extensor digitorum communis (EDC) and flexor digitorum superficialis (FDS) of both hands was recorded throughout the entire test. Electrical activity (EA) and median frequency (MDF) were calculated, and then regressed against the time courses to obtain the slopes of progress. Further analysis of the EMG parameters was done by the joint analysis of spectra and amplitudes (JASA). The results indicated that maximum voluntary electrical activation (MVE) decreased after 2-h typing, and did not recover to the initial values even after a 10-min break. Besides, there was a trend of decrement in frequency throughout the entire trail, and the MDF reduced by 25% in comparison with the initial values. With the JASA plot, 74% of the muscles manifested fatigue after 2-h typing activity. Furthermore, we observed that the EDC muscles were more susceptible to muscular fatigue than the FDS muscles. In conclusion, prolonged consecutive typing may induce muscular fatigue in the healthy typists even in an ergonomic typing environment.