Research On Exposure-effect Relationship Between Muscular Load And Fatigue Of Automobile Assembly Workers’ Waist And Wrist

Objective:To analyze the changes of blood biochemical indicators, electrophysiology indicators and heart rate in the course of waist and wrist muscle fatigue associated with tool weight, table height and posture repetition while simulating bend overs and crew driver operation.Methods:According to tools weight (1kg,1.5kg and 2kg) and work surface table height (0.5m,0.75m, lm) to crossover design nine experimental groups. The 24 volunteers were randomly divided into three groups(A, B and C), with eight subjects in every group. Three groups of subjects completed nine tests according to the rounds.Every subject complete the continuous repetitive simulation screwing operation in accordance with five frequency loads(0,90,135,180 and 225 times). The waist and wrist muscles’ratings of perceived exertion (RPE) were observed as subjective indicators of fatigue. The finger blood samples were taken for detecting lactate (LA), and venous blood for creatine kinase (CK), lactate dehydrogenate (LDH) as well as calcium (Ca2+) in five minutes interval between two repetitiveness loads as biochemical indicators. The surface electromyography signal (sEMG) and pulse rates were collected in the entire process test as physiological indicators, including root mean square (RMS) and mean frequency (MF). Results:1. All the twenty-four volunteers’ age (24.80±1.27 years), height (174.72±4.25cm), weight (68.92±6.08kg) etc. comply with the criteria of homogeneity.2. RPE and pulse rates changes:① With the increase of height load, the waist and wrist muscles’RPE and pulse rates showed square trend rise (P<0.05), culminated in the H2 group. The trends of waist muscles’RPE and pulse rate were similar.②With the increase of weight load, the wrist muscules’ RPE and pulse rates showed a linear trend increase.③With the increase of frequency load, the waist and wrist muscles’ RPE showed quadranomial increasing trend (fast then slow down), pulse rates showed an trinomial increasing trend (increased rapidly then maintained a high level state). The RPE and pulse rates of R2 group were significantly higher than the values of R1 group.④With the increase of the number of trials, the values of the waist and wrist muscles’RPE and pulse rates in S2 and S3 group was significantly lower than the values in S1 group, showed a square trend and overall decline.3. Biochemical indicators’changes:①With the increase of height load, there were significant changes of CK, LDH and Ca2+. Blood CK and Ca2+ changed with square trends. CK was culminated in H2 the group. Ca2+ was culminated in the H3 group.②With the increase of weight load, there were significant changes of CK, LDH and Ca2+. Blood CK and Ca2+ changed with square trends, both culminated in the H2 group.③With the increase of frequency load, there were significant changes of CK, LDH and LA. CK was rapidly rising with cubic trend; LDH showed first cubic trend with slowly rising then stabilized in the groups of R2-R5. LA showed linear rising trend, with rapid increasing in the Rl and R2 groups, then keep a high level.④ With the increase of the number of trials, there were significant changes of CK and Ca2+. CK value declined overall with square trend, lowest in S2. Ca2+ value increased overall with square trend, culminated in S2.4. EMG indicators’ changes:①With the increase of height load, there were significant changes of the RMS values of BR, FC, BB, DM,ES and the MF values of FC, ES. All of the above indicators showed square trend. (The values of RMS_BR, RMS_FC, MF_FC were lowest in H2 group. The values of RMS_BB, RMS_DM, RMS_ES and MF_ES were highest in H2 group.)②With the increase of weight load, there were significant changes of the RMS values of BR, DM and the MF values of BR, BB, DM, ES. All above indicators showed downward trends integrally. RMS_BR, RMS_DM, MF_BR, MF_ES have square trend. MF_BB, MF DM have linear trend.③With the increase of frequency load, there were significant changes of the values of BR, FC, EC, RES and the MF value of FC. The RMS values of BR, FC, EC rapidly decreased then maintain low level. The MF_FC slowly decreased then maintain low level. The RMS value of RES changed with down-up, finally back to the initial state.⑤With the increase of the number of trials, there were significant changes of the RMS values of BR, EC, BB, DM, ES and the MF values of BR, FC, DM, ES. The RMS values of BR, EC, DM, RES and the MF values of BR, FC, DM showed linear changes. RMS_BR, RMS_EC, MF_BR, MF_FC and MF_DM present linear increase. RMS_DM, RMS_RES present linear decrease. RMS_BB, RMS_LES and MF_ES showed square trends, lowest in the S2 group and the S2 and S3 group was significantly lower than S1.5. The correlations among external load, internal load and fatigue:① With the increase of height load, waist RPE and CK share similar trends. The changes of waist RPE and pulse rates were consistent with the MF_ES and RMS_ES, and in contrast with RMS_FC. The changes of wrist RPE were consistent with the RMS_DM, and in contrast with MF_FC, MF_EC and RMS_BR.②With the increase of weight load, waist RPE and LDH share similar trends. The wrist RPE and pulse rates were in contrast with RMS_BR, RMS_DM, MF_BR, MF_BB, MF DM and MF ES.③With the increase of frequency load, RPE and blood CK, LDH, LA share similar trends, showing raising trends. RMS_BR, RMS_FC, RMS_EC and MF_FC present decreased trends.④With the increase of the number of trials, the changes of waist RPE and pulse rates were consistent with the MF_ES and RMS_ES. With the increase of the number of trials, the changes of wrist RPE were in contrast with MF_BR, MF_FC, RMS_BR, RMS_EC and consistent with MF_BB, RMS_BB, RMS_DM.⑤ correlation analysis and polynomial model fit, the results show:Wrist RPE weight load, frequency, test sequence, pulse rates. Waist RPE was significant correlation with frequency, pulse rates. Waist RPE and frequency were highly positive correlation. CK、Ca2+、LA was significant correlation with frequency and PRE. LDH was significant correlation with weight load. All of the BR, FC, EC, DM, BB’s sEMG were moderate correlated with weight load and frequency. Both of the RMS_ES, MF_ES were low correlated with height load, frequency and Waist RPE.⑥Make fit better dose-effect relationship for the correlation between good indicators:(1)RPE_wan=(-0.56+2.14R-0.52R2+0.046R3+0.089S2-0.45S+0.19M)RPE_wan0(2)CK=1.003CK0+0.158%R3×CK0(3)CK=(0.8670+2.3601%R2-1.5051%R2×S+0.3184%R2×S2+12.3800%M-2.8406%M2)×CK0(4)RMS_EC=[1.57+3.53%R2-27.13%R+7.95%H2-30.84%H-5.03%M]RMS_EC0(5)CK=[1.0064+3.42%(RPE_wan/RPE_wan0-1) 2]CK0(6)CK=[1.019+4.31%(RPE_yao/RPE_yao0-1)2]CK0(7)RMS_FC [1.00098-0.0571(RPE_wan/RPE_wan0)]RMS_FC06. Correlations among objective indicators:Low degree correlations among CK, Ca2+, LDH were significant. Moderate degree correlations among RMS_FC, RMS_EC, RMS_BR were significant. Low degree correlations among MF_FC, MF_EC, MF_BR were significant.Conclusion:① biochemical indicators:CK, LDH concentration occurred with significantly increased fatigue, muscle fatigue is reflected sensitive and effective, reliable and objective indicators for evaluation of low load repetitive activities, fatigue process.② EMG indicators:the EMG wrist extensor muscles measured showed a more pronounced and stable trend, the research arm of muscle fatigue reliable objective indicators for low load repetitive wrist fatigue evaluation activities process.③ load because of the many variables, frequency load and subjective and objective indicators of fatigue showed better correlation and dose-response relationship, where the waist, wrist RPE and frequency of high positive correlation, CK and frequency load of moderate positive correlation, RMS and frequency load wrist extensor moderate negative correlation.④ between subjective and objective indicators, CK and waist, wrist RPE moderate positive correlation between the wrist and the wrist extensor RMS RPE moderate negative correlation. CK, Ca2+, LDH good correlation, wrist flexor, the correlation between sEMG wrist extensors, brachioradialis the three well. Frequency load with RPE, CK, there is a good correlation and effect relationship between the RMS_EC.⑤ single wrist to the working environment, tools weight not only affects the occurrence of fatigue wrist, waist change will indirectly bear the external load, thus affecting the incidence of lower back fatigue. Wrist muscle fatigue significantly increases the incidence of reduced proficiency test.Key Words:...