Effect evaluation of a wearable exoskeleton chair based on surface EMG

Standing for a long time increases the health risks for work-related industrial workers. A wearable exoskeleton chair (referred to as chairX in this paper for brevity) was designed and built by Huazhong University of Science and Technology to reduce the stress on the leg muscles of long-standing workers, which reduced the risk of muscle injury. We evaluated the effect of chairX by measuring the surface Electromyography (EMG) of the biceps femoris (BF), rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) during different tasks. Six healthy subjects were recruited to perform squatting tasks at different knee bending angles $(107^{\circ}, 121^{\circ}, 132^{\circ})$ and loads (0, 10 kg, 20 kg) with or without chairX. The experimental data showed that the chairX was able to significantly reduce the activation levels of the muscles at different bending angles and loads, and the muscle activity decreased by about 80% on average; at the same bending angle, the activation levels of the muscles increased with the increase of the loads, and the muscle activities decreased by about 82% on average; the activation levels of muscles decreased with the increase of bending angle, and the muscle activities decreased by about 83% on average, when the loads were the same; In contrast, female subjects had higher activation levels of muscles than male, with an average decrease of 87% and 73%, respectively. This investigation indicates that chairX effectively reduces the physical burden of workers and may increase productivity.