AUTHOR=Wang Zhuo , Wu Xinyu , Zhang Yu , Chen Chunjie , Liu Shoubin , Liu Yida , Peng Ansi , Ma Yue 

TITLE=A Semi-active Exoskeleton Based on EMGs Reduces Muscle Fatigue When Squatting

JOURNAL=Frontiers in Neurorobotics

VOLUME=Volume 15 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/neurorobotics/articles/10.3389/fnbot.2021.625479

DOI=10.3389/fnbot.2021.625479

ISSN=1662-5218

ABSTRACT=In this paper, a semi-active exoskeleton used to reduce the muscle fatigue of the lower limb was designed and evaluated. Background: The advantages and disadvantages of assistive exoskeletons developed for industrial purposes were introduced. Simulation: The process of squatting was simulated in the AnyBody.7.1 software, the result showed that muscle activity of the gluteus maximus, rectus femoris, vastus medialis, vastus lateralis, vastus intermedius and erector spinae increased with increasing of knee flexion angle. Design: The exoskeleton was designed with three working modes: rigid-support mode, elastic-support mode and follow mode. Rigid-support mode was suitable for scenes where the squatting posture is stable, while elastic-support mode was beneficial for working environments where the height of squatting varied frequently. The working environments were identified intelligently based on the EMGs of the gluteus maximus and quadriceps, and the motor was controlled to switch the working mode between rigid-support mode and elastic-support mode. In follow mode, the exoskeleton moves freely with users without interfering with activities such as walking, ascending and descending stairs. Experiments: Three sets of experiments were conducted to evaluate the effect of exoskeleton. Experiment one was conducted to measure the surface electromyography signal (EMGs) , the root mean square of EMG amplitude of soleus, vastus lateralis, vastus medialis, gastrocnemius, vastus intermedius, rectus femoris, gluteus maximus and erector spinae  were reduced by 98.5%, 97.89%, 80.09%, 77.27%, 96.73%, 94.17%, 70.71% and 36.32% respectively with the assistance of the exoskeleton. The purpose of experiment two was to measure the plantar pressure. With exoskeleton, the percentage of weight through subject's feet was reduced by 63.94%, 64.52% and 65.61% respectively at 0, 60 and 120 degrees of knee flexion angle. Experiment three was purposed to measure the metabolic cost at a speed of 4km/h and 5km/h with and without exoskeleton. experiment results show that the average additional metabolic cost introduced by exoskeleton was 2.525% and 2.85%. It indicated that the exoskeleton would not interfere with the movement of the wearer seriously in follow mode. Conclusion: The exoskeleton not only effectively reduced muscle fatigue, but also avoided interfering with the free movement of the wearer.