Abstract
Background: Workers in industry often perform repetitive and monotonous tasks with light weights, resulting in low back disorders. Objective: The objective of this study was to quantitatively estimate when the muscle fatigue of the lower back muscles becomes substantial during a repetitive lifting task. Methods: sEMG of the erector spinae muscle was recorded during the procedure of repetitive load lifting of 13.84 kg ± 4.22 kg from the floor to a 0.75 m height table. The fatigue rate determined by the surface Electromyography recordings was compared with the participant’s self-evaluated fatigue level values. Eight healthy male subjects executed sixty-four load lifts divided in four lifting trials with a five minutes rest-break between each lifting trial. Results: Analysis of surface Electromyography frequency domain parameters indicated that the fatigue accumulation was minimized after a rest break in the first three lifting trials while at the beginning of the 4th lifting trial, the fatigue accumulation level was high, implying the substantial fatigue onset. The fatigue rate values were found to be -0.417 Hz/Load Lift at the end of the 3rd lifting trial and -0.637 Hz/Load Lift at the beginning of the 4th lifting trial implying the substantial fatigue accumulation onset. Conclusions: The findings showed that there was a 25% time lag to the participant's self-evaluated substantial fatigue level perception. A new index was introduced for the determination of the Time to Substantial Fatigue Onset in comparison with the corresponding one established by NIOSH lifting analysis.
Highlights
Workers in some industries are exposed to ergonomically unfavorable working conditions leading to work-related musculoskeletal disorders (MSDs) [1]
Other investigators failed to find any gender differences in EMG [20] in this study was assumed that the same gender as well as the almost same age of participants reduced the variability of the muscle characteristics from person to person
SEMG study Statistical analysis results of median power frequency (MF) data normality distribution are shown in table 4
Summary
Workers in some industries are exposed to ergonomically unfavorable working conditions (repetitive motions, dynamic working postures) leading to work-related musculoskeletal disorders (MSDs) [1]. Repetitive and monotonous tasks with even lightweights result in accumulated local muscle fatigue which is a serious problem in the workplace, and can cause muscle injuries [3]. Such injuries may be caused by repetitive motion and cumulative fatigue, rather than heavy loading [3,4]. Workers in industry often perform repetitive and monotonous tasks with light weights, resulting in low back disorders
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