Objective To examine changes of blood biochemical indicators in the course of wrist muscle fatigue associated with tool weight and movement repetition in operating screw driver simulation.
Methods Twenty-four volunteers were recruited randomly into three groups divided by tool weights of 1,1.5,and 2 kg.Each group was asked to continuously complete repetitive simulation tasks containing five repetitiveness loads for 0,90,135,180,and 225 times.The finger blood samples were taken for detecting lactate (LA),and venous blood samples for creatine kinase (CK),lactate dehydrogenate (LDH),and calcium (Ca2+) in fiveminute interval of each load as biochemical indicators.The rating of perceived exertion (RPE) of wrist muscles was recorded as subjective indicator of fatigue.
Results All the twenty-four volunteers' age(24.80& #177;1.27) years,height(174.72& #177;4.25) cm,weight(68.92& #177;6.08) kgwere homogenous.The RPE scores showed a linearly rise with increase in tool weight load (P < 0.000 1) and a quartic rise with increase in repetitiveness load (P < 0.000 1).There were significant changes of blood CK and Ca2+ concentrations among the three weight load groups (P < 0.05 or P < 0.01).There were significant changes of blood CK,LDH,and LA concentrations among the five repetitiveness load groups (P < 0.05 or P < 0.01) that appeared rising tendencies with higher repetitiveness load (P < 0.05).Moderate positive correlations were identified among CK,repetitiveness load,and RPE,with coefficients of 0.630 1,0.812 1,and 0.589 6,respectively.Low positive correlations were identified between LA and repetitiveness load,as well as between LA and RPE,whose coefficients were 0.182 5 and 0.216 7 respectively.For biochemical indicators,moderate positive correlations were significantly shown among CK,LDH,and Ca2+,with a similar drop-rise tendency,and the coefficients were 0.329 5,0.501 5,and 0.434 2 respectively.
Conclusion Blood CK,LDH,and LA prove to be sensitive objective indicators associated with the degree of muscle fatigue caused by low-load repetitive activities.There are obvious correlation and exposure-effect relationships among repetitiveness,RPE,and CK.Repetitiveness load appears to be an important factor causing low-load fatigue,suggesting that appropriate work assignment would be beneficial to alleviating muscle fatigue.
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