Development of Soft Wearable Device for Muscular Assist and Posture Guide at Lifting

Abstract

There is a saying: comfortable posture is usually bad posture. A human feels comfortable and consumes less energy when holding the object on the floor by flexing his back than bending leg, because of characteristics of human body design. However, from a spinal point of view, lifting a heavy load in a back bent posture is a dangerous act that may increase the risk of a disc injury by 2 to 4 times. We have developed a soft wearable device that can reconfigure these contradictory human body systems to make to feel the correct posture comfortable and bad posture uncomfortable. A representative posture correction functions of this device is to correct the wearers habit to use a lifting technique called squat instead of the stoop and to induce wearer to keep his knee behind the toes in the process of bending the legs. Experiments with varying lift posture showed that this device interfered with the stoop motion but assisted the squat motion. Also, we proved that the muscular force assistive effect of the device increased in knee backed posture. Another experiment was conducted in which the 15kg box was repeatedly lifted at a rate of 10lifts/min for 6minutes. In case of taking squat posture, EMG values of spinal erector, biceps femoris, and rectus femoris decreased by 14.0%, 17.0%, and 14.3% respectively when wearing the device. Also, in this case, the metabolic energy cost decreased by 29.5% and the heart rate decreased by 13.6%, proving that the device is effective in reducing fatigue of the worker. Compared to stooping without a device, the result was a 24.7% reduction in metabolic energy cost and a 7.3% reduction in heart rate when the subject takes squat posture with wearing the device. Therefore, the device is expected to help stuff transportation workers to lift objects in correct posture with small fatigue.