Time Interval to Reduce Cumulative Effect of Fatigue during Repetitive Trunk Extension Task

摘要

The purpose of the study is to investigate the relationship between the trunk muscle fatigue and recovery time during repetitive trunk extension by using a surface electromyogram(EMG). Ten healthy subjects participated in a simulated lifting task with five levels of recovery time and three levels of sub-maximal contraction. EMG signals of the L1 and L3 level of the erector spinae muscle were recorded, and analyzed in terms of MPF(mean power frequency) parameter to quantify the level of muscle fatigue. It was found that MPF significantly (P < 0.05) decreased during repetitive extension task at 50 % and 75 % sub-maximal contractions. Then it took three minutes for the trunk muscle to recover from fatigue during 50% sub-maximal contraction, and it took five minutes during 75% sub-maximal contraction. The recovery time estimated by the metabolic cost was found to be relatively short for the trunk muscle to fully recover from fatigue. In conclusion, the information of muscle fatigue and recovery time need to be considered in order to prevent workers from musculoskeletal injuries due to cumulative fatigue during repetitive lifting task.