Many human movements can be aided by exo-suit. One of them is that humans put a lot of strain on their knee and waist joints while lifting large objects, but using an exo-suit can lessen the risk. However, since the weight of the exo-suit itself acts as an additional burden on body, an appropriate torque distribution strategy considering the entire system is necessary. To solve this problem, this paper proposed an assistive technique based on whole-body control. Meanwhile, when the legs are fully extended during torque control, the system has a singularity problem and the required torque will be highly increased. Singularity is serious problem because it is essential to fully straighten the legs during the lifting operation. In this paper, this problem was solved by adding a straight-leg term to the whole-body control cost function. The feasibility of the proposed method was verified through simulation, and it was shown that the exo-suit could stably perform lifting motions due to the method.

[Purpose]The purpose of this study was to examine changes in muscle fatigue of the erector spinae, rectus abdominis, quadratus lumborum, and gluteus maximus muscles during repetitive lifting using the squat-to-lift and stoop-to-lift techniques. [Method] Participants were 17 healthy young students in their 20 s. The change in the median frequency of the surface electromyography signal was calculated between baseline and the fatigue trial, where fatigue was self-reported. [Results] A significant decrease in median frequency was identified for the quadratus lumborum and gluteus maximus muscles using the squat-to-lift technique (p < 0.05). [Conclusion] The squat-to-lift technique is associated with fatigue of the quadratus lumborum and gluteus maximus muscles and may not be preferable to the stoop-to-lift technique in all cases.