Can We Redesign a Shoulder Exosuit to Enhance Comfort and Usability Without Losing Assistance?

Reduced shoulder mobility limits upper-limb function and the performance of activities of daily living across a wide range of conditions. Wearable exosuits have shown promise in assisting arm elevation, reducing muscle effort, and supporting functional movements; however, comfort is rarely prioritized as an explicit design objective, despite it strongly affects real-life, long-term usage. This study presents a redesigned soft shoulder exosuit (Soft Shoulder v2) developed to address comfort-related limitations identified in our previous version, while preserving assistive performance. In parallel, assistance was also improved, shifting from the coronal plane to the sagittal plane to better support functionally relevant hand positioning. A controlled comparison between the previous (v1) and redesigned (v2) modules was conducted in eight healthy participants, who performed static holding, dynamic lifting, and a functional pick and place task. Muscle activity, kinematics, and user-reported outcomes were assessed. Both versions increased endurance time, reduced deltoid activation, and preserved transparency during unpowered shoulder elevation. However, the difference between them emerged most clearly during functional tasks and comfort evaluation. The redesigned module facilitated forward arm positioning and increased transverse plane mobility by up to 30 deg, without increasing muscular demand. User-reported outcomes further indicated a substantial improvement in wearability, with markedly lower perceived pressure and higher ratings in effectiveness, ease of use, and comfort compared to the previous design. Taken together, these findings show that targeted, user-centered design refinements can improve comfort and functional interaction without compromising assistive performance, advancing the development of soft exosuits suitable for prolonged and daily use.

Sensorless model-based tension control for a cable-driven exosuit

Cable-driven exosuits have the potential to support individuals with motor disabilities across the continuum of care. When supporting a limb with a cable, force sensors are often used to measure tension. However, force sensors add cost, complexity, and distal components. This paper presents a design and control approach to remove the force sensor from an upper limb cable-driven exosuit. A mechanical design for the exosuit was developed to maximize passive transparency. Then, a data-driven friction identification was conducted on a mannequin test bench to design a model-based tension controller. Seventeen healthy participants raised and lowered their right arms to evaluate tension tracking, movement quality, and muscular effort. Questionnaires on discomfort, physical exertion, and fatigue were collected. The proposed strategy allowed tracking the desired assistive torque with an RMSE of 0.71 Nm (18%) at 50% gravity support. During the raising phase, the EMG signals of the anterior deltoid, trapezius, and pectoralis major were reduced on average compared to the no-suit condition by 30%, 38%, and 38%, respectively. The posterior deltoid activity was increased by 32% during lowering. Position tracking was not significantly altered, whereas movement smoothness significantly decreased. This work demonstrates the feasibility and effectiveness of removing the force sensor from a cable-driven exosuit. A significant increase in discomfort in the lower neck and right shoulder indicated that the ergonomics of the suit could be improved. Overall this work paves the way towards simpler and more affordable exosuits.