Effects of wearable power assist device on low back fatigue during repetitive lifting tasks

Background: A wearable power assist device was developed to reduce the stress on the lower back by using pneumatic muscles. The purpose of this study was to explore whether the assist device could reduce the activity or fatigue of lower back muscles during a repetitive lifting task. Methods: Twelve male subjects participated in the study. Electromyography of the thoracic erector spinae at the T9 level and lumbar erector spinae at the L3 level was recorded during 90 lifts in 15 min. Subjects' heart rate and Borg's Rate of Perceived Exertion Scale score were recorded during lifting sessions. Findings: The electromyography amplitude of thoracic erector spinae and lumbar erector spinae was only increased by 32.45% and 40.17%, respectively, when the wearable power assist device was used when comparing the pre- and post-lifting task. Whereas it was increased by 125.78% and 85.90%, respectively, when the wearable power assist device was not used. The decrease in electromyography median frequency from the start until the end of the lifting session was significantly lower when wearing the assist device for the thoracic erector spinae (2.72% vs 7.45%) and the lumbar erector spinae (3.91% vs 13.70%). Use of the assist device also significantly reduced the percentage change in heart rate and Borg Scale (p < 0.05). Interpretation: The use of the wearable power assist device showed less back muscle contraction compared to the no-use, which can potentially minimize the level of back muscle fatigue across the lifting session.