Effects of ankle exoskeleton assistance during human walking on lower limb muscle contractions and coordination patterns

踝关节外骨骼可用来提高人的行走效率，辅助老年人、运动功能障碍患者等进行日常活动或康复训练，但外骨骼的助行模式会对穿戴者的下肢肌肉激活与协调模式产生影响。本文利用一款绳驱动踝关节外骨骼，设计了不同助力时机与助力大小组合的助行模式，采集了7名穿戴者在跑步机上以1.25 m/s速度水平行走时的下肢表面肌电信号，研究不同助行模式对穿戴者下肢肌肉激活与协调模式的影响。实验结果表明，比目鱼肌激活程度在踝关节外骨骼助力时有明显降低，在助力时机为步态周期49%、助力大小为0.7 N·m/kg时，最高可降低（38.5 ± 10.8）%。并且，相对于助力时机，助力大小对比目鱼肌激活程度影响更为显著。踝关节外骨骼不同模式助行时，所测量下肢肌肉可分解为5个基本协同模式，且合适的助力时机与助力大小条件下，下肢肌肉协调模式和正常行走相比改变较小。此外，比目鱼肌-胫骨前肌、股直肌-半腱肌的协同收缩度在外骨骼助力时比正常行走均有升高。本研究有助于理解健康穿戴者如何调整自身的神经肌肉控制机制来适应不同外骨骼助力，并为选择合适的助行模式以及合理利用外骨骼提高行走效率提供依据。.; Lower limb ankle exoskeletons have been used to improve walking efficiency and assist the elderly and patients with motor dysfunction in daily activities or rehabilitation training, while the assistance patterns may influence the wearer's lower limb muscle activities and coordination patterns. In this paper, we aim to evaluate the effects of different ankle exoskeleton assistance patterns on wearer's lower limb muscle activities and coordination patterns. A tethered ankle exoskeleton with nine assistance patterns that combined with differenet actuation timing values and torque magnitude levels was used to assist human walking. Lower limb muscle surface electromyography signals were collected from 7 participants walking on a treadmill at a speed of 1.25 m/s. Results showed that the soleus muscle activities were significantly reduced during assisted walking. In one assistance pattern with peak time in 49% of stride and peak torque at 0.7 N·m/kg, the soleus muscle activity was decreased by (38.5 ± 10.8)%. Compared with actuation timing, the assistance torque magnitude had a more significant influence on soleus muscle activity. In all assistance patterns, the eight lower limb muscle activities could be decomposed to five basic muscle synergies. The muscle synergies changed little under assistance with appropriate actuation timing and torque magnitude. Besides, co-contraction indexs of soleus and tibialis anterior, rectus femoris and semitendinosus under exoskeleton assistance were higher than normal walking. Our results are expected to help to understand how healthy wearers adjust their neuromuscular control mechanisms to adapt to different exoskeleton assistance patterns, and provide reference to select appropriate assistance to improve walking efficiency.