Muscle Synergy Analysis of Healthy Subjects Using a Soft Elbow Exosuit During Load-Carrying Tasks

Soft assistive wearable robotics, or soft exosuits, have shown great potential in enhancing human motor function while preserving the user's natural movement. They are increasingly used to reduce fatigue and the risk of injury during physically demanding tasks and everyday activities. A deeper understanding of how assistive forces from soft exoskeletons influence muscle coordination during various tasks is crucial for developing optimized control and rehabilitation strategies for these devices. This study investigates muscle synergies in healthy participants carrying loads, as often performed in daily activities, over an extended period, both with and without the assistance of a soft elbow exosuit. Synergies similarity was analyzed by comparing the extracted patterns in both conditions, as well as their composition in terms of muscle contributions. The results show that, on average, in the with-exosuit condition fewer synergies are required to explain the performed movements. This suggests the idea that the assistive device "aggregates" motor primitives while reducing muscle activation. Furthermore, we found that synergies dominated by the wrist flexor, biceps, and infraspinatus were not altered by the exosuit assistance. However, the deltoid-dominated synergy observed during load carrying without the exosuit was altered by the exosuit assistance, shifting to a triceps-dominated synergy.