Brachial Plexus Injuries (BPIs) often lead to significant motor function impairment, severely limiting a patient's ability to control the affected muscles. Nerve transfer surgery is a commonly used intervention designed to restore muscle function by reinnervating paralyzed muscles. This study aims to evaluate the effectiveness of reinnervation in the biceps brachii following nerve transfer surgery, using High-Density Surface Electromyography (HD-sEMG) and measurements of functional force production. The study involved patients who had undergone nerve transfer surgery after BPI, with data collected from both healthy and affected biceps. HD-sEMG signals and force measurements were recorded during specific motor tasks. Patients performed both trapezoidal contractions and fatiguing tasks at two distinct force levels: 20\% and 60\% of Maximum Voluntary Contraction (MVC).