Measurement of trunk muscle fatigue during dynamic lifting and lowering as recovery time changes

The purpose of this study was to identify the relationship between the cumulative fatigue of trunk muscles and the recovery time during dynamic lifting and lowering in symmetric and asymmetric postures. Ten subjects participated in the experiment. Recovery times of 1, 2, 3, 4, or 5 min were applied, respectively, during a 9 min period of lifting and lowering. The lifting weight was set equal to 25% of the individual's maximum voluntary condition (MVC); a lifting frequency of 4 lifts/min was used. Electromyography (EMG) signals from 10 trunk muscles were collected and analyzed in terms of mean power frequency (MPF) before and after the lifting/lowering tasks. Fatigue level was analyzed by using analysis of variance (ANOVA). As a result, a partial recovery was observed from 3 min recovery time during symmetric lifting. In 4 min, 70% of subjects experienced a recovery of at least two trunk muscles in symmetric lifting and 10% in asymmetric lifting. In 5 min recovery time, 90% of the subjects showed a recovery of at least two trunk muscles in symmetric lifting, and 50% in asymmetric lifting. It should be noted that not all subjects were recovered in 5 min.In conclusion, proper work/rest ratios based upon the level of individual muscle fatigue may be used as an early intervention to prevent muscle fatigue in the workplace. In addition, designing an ergonomic workplace would require incorporating data from this study with other factors.Relevance to industryThe results from this study could help ergonomists design the length of recovery time during the work cycle to control the cumulative fatigue of trunk muscles in industry with repetitive lifting/lowering tasks.