Experimental Study On The Muscle Fatigue Of Upper Limbs During Repetitive Performance With SEMG

Objective To estimate muscle fatigue and workload in repetitive work by using surface EMG is an important aspect in ergonomics. But the typical sEMG signal changes of muscle fatigue are based on static contractions and it is doubtful that use amplitude and spectrum parameters in dynamic contractions. This experiment is aim to determine the muscle fatigue and its state of upper limb muscles during repetitive performances with sEMG and estimate the suitability of some EMG parameters.Methods 8 student volunteers in seat position were required to grasp a round part weighted 5g from one plate to another whose distance is 30cm with right hand. The volunteers are healthy without any muscular impairment before experiment and sign the agreement to fulfill experiment. The frequency of movement was 40 times/min for 8 minutes to simulate a repetitive work in the laboratory. The EMG signal was recorded simultaneously from Brachioradialis, Biceps, Deltoid and Trapezius then analyzed with amplitude, spectrum or combined indices which called the joint analysis of EMG amplitude and spectrum (JASA).Results As increase of the performance time, the amplitude in MVE% of the 4 muscles showed an increase tendency, and all the MVE%<20%, although it was not significantly (P>0.05). EMG spectrum analysis showed the mean frequency (MF) and the mean power frequency (MPF) decreased along with the performance that means the left shift of frequency. However, the frequency didn't decrease but increase during the last 2 time periods. The slope of MF from all the muscle was negative at the first time period and sometimes negative or positive during other time intervals. The MPF and its slope showed the same changes. According to JASA method, the muscles existed changes in fatigue, recovery and load increase.Conclusions The muscles showed such function changes as fatigue, recovery, load increase or re-fatigue during the period of repetitive work. Mainly involved were muscles of Trapezium, Deltoid and Brachioradialis but Biceps was relatively less. The EMG parameters such as MVE%, MF and MPF and especially their changes during the performance were still able to indicate muscle fatigue during repetitive work, which was demonstrated further by the JASA method.