Research On The Effects Of Time And Workload On Work Fatigue Of Manual Materials Handling Based On SEMG And ECG

With the continuous improvement of the overall economic level.living conditions and medical technology,people have been paying more and more attention to occupational physiology and mental health.The academic and medical circles are trying to explore and identify risk factors of occupational fatigue in order to reduce their negative impacts on workers,enterprises and society.However,owing to the regional economic level,geographical location,educational level,social status and many other factors,manual materials handling(MMH)which is of long term,heavy workload and poor environment has not been attached enough importance,leading to a serious impact on occupational health and life quality of MMH workers.This paper explores the effects of time and workload on fatigue of the MMH workers.The main contents include:(1)Collecting and reading the existing researches to determine the main risk factors of fatigue in MMH tasks,resulting with working time and workload.And Borg’s fatigue scale,surface Electromyography(sEMG)and Electrocardiogram(ECG)were chosen to measure fatigue during MMH.(2)Designing MMH experiment and collecting subjective fatigue,sEMG and ECG datas during MMH,then processing the raw datas correctly.(3)Analyzing the relationship between subjective fatigue,sEMG,ECG indexes and working time and workload,and the relationship among subjective and objective indexes,thus exploring the influence of work factors on body fatigue.The main conclusions of the study are as follows:(1)Subjective fatigue score shows a good linear trend with working time and workload(Goodness of Fit>0.75,Sig.<0.01).The longer the working time,the faster the subjective fatigue rises;the greater the workload,the earlier the subjective fatigue comes.(2)The results of sEMG shows that the time-domain index(intergrated EMG)and frequency-domain index(Median Frequency)increased and decreased with the prolongation of time separately,indicating that muscle fatigue appears and accumulates during MMH.Both intergrated EMG and Median Frequency have good linear trends with the growth of workload(Goodness of Fit>0.62,Sig.<0.01).The difference of trapezius muscle indexes before and after MMH are significantly higher than those of the erector spine(for intergrated EMG t=-6.652,Sig.<0.01;for Median Frequency t=-2.605,Sig.<0.05),indicating that the shoulder was suffering from more fatigue than waist.In addition,the results of sEMG is consistent with the subjective fatigue score and both can be used as the observation indexes of fatigue.(3)The results of ECG measurements shows that the Heart Rate(or R-R interval mean)increased(or decreased)rapidly to a certain level after the beginning of MMH and then fluctuated above and below the level.The Heart Rate Variability(HRV)indexes Low Frequency(LF)and Balance Ratio(LF/HF)increases significantly after MMH(for LF t=-32.673,Sig.<0.01;for LF/HF t=-9.653,Sig.<0.01)while High Frequency(HF)decreases,indicating that sympathetic nerve activity increases while parasympathetic nerve is inhibited,showing that the mental fatigue state deepenes,and LF and LF/HF appeares a linear trend with workload during MMH(Goodness of Fit>0.72,Sig.<0.05).In addition,the correlation between heart rate and subjective fatigue is not strong,but the correlation between Heart Rate Variability of mental fatigue and subjective fatigue score is quite obvious(R>0.80,Sig.<0.05),indicating that the subjective fatigue state may be affected by mental fatigue during MMH.The research contents and conclusions of this paper are an important supplement to the study of MMH fatigue,which can provide reference for the fatigue measurement of workers,the improvement of MMH tasks and the establishment of shift system and the development of new MMH standards.