Background and research objective - Approximately 80\% of stroke patients experience upper limb motor impairments, including spasticity, muscle weakness, and abnormal synergies, which complicate daily activities. Accurate quantification of motor impairments is essential for optimizing rehabilitation strategies after a stroke. Objective and automatic assessment can be achieved with robotic devices. The Shoulder Elbow Perturbator (SEP) applies controlled mechanical perturbations to assess elbow and shoulder impairments. During these measurements, the wrist is fixated using plastic clamps with foam padding. But these clamps cause discomfort, positioning inconsistencies, instability, and unintended hand movemen. This study aims to design and evaluate an alternative fixation method for securing the arm in the SEP.

Method and results - A design thinking approach was applied. During brainstorming, concepts focused on arm conformity, rigidity, load distribution, and unrestricted elbow rotation. Based on a Harris profile, a lightweight vacuum brace was developed into a functional prototype, and clamps were redesigned to fit the brace. Validation experiments were performed with eight healthy participants tested in the SEP with both the vacuum brace and original rigid clamps. Comfort was assessed via questionnaire. Additionally, SEP angle and torque, and arm motion capture data were collected. The vacuum brace significantly reduced discomfort from severe to slight. SEP and motion capture data showed comparable fixation stability during multisine tasks. During passive stretch trials, lower intraclass correlation coefficients for stiffness estimation increased elbow displacement, and occasional movement within the clamps were observed with the brace, indicating reduced fixation performance.

Conclusions - The vacuum brace improved participant comfort during robotic assessment of upper limb motor impairments. Fixation stability was comparable during multisine perturbation tasks but reduced during stretch tasks, likely due to the current clamp design.