This assessor-blinded, two-arm randomized controlled trial compares device-assisted balance training added to conventional physiotherapy with conventional physiotherapy alone in adults with unilateral subacromial impingement syndrome. The treatment period is six weeks. The primary outcome is the change in Central Sensitization Inventory. Secondary outcomes include shoulder pain and disability, fear of movement, pressure pain thresholds, and static and dynamic balance. Outcomes are assessed at baseline and immediately after treatment.