Surgical procedures often induce discomfort and strain on the upper extremities, impacting task performance, and contributing to musculoskeletal disorders. To address this, a surgical arm assistance system has been developed, aiming to alleviate upper limb strain and improve task performance during surgery. This study investigates the impact of different shapes and sizes of distal forearm supports on the range of motion (pronation/supination). Without support, a flat shape and five anthropomorphic shapes are evaluated. Thirty subjects perform maximal pronation and supination tasks, with angles measured using a digital device. Results indicate that larger anthropomorphic shapes allow greater rotation angles, albeit still less than without support or with a flat support. The influence of surgical gowns on task execution is also examined. Subjective assessments reveal preferences for anthropomorphic shapes and positive ratings for surgical gown use. While limitations exist in task selection and interaction time, this study highlights the significant influence of the forearm support shape on rotational movements. Further research will optimize arm assistance systems for dynamic precision tasks during surgery.