Gait alterations associated with conditions such as cerebral palsy, stroke, and knee osteoarthritis require accurate, accessible, and integrated assessment tools. This paper presents the design and validation of a portable device for the simultaneous measurement of knee joint kinematics and muscle activity in the sagittal plane. The system combines a Hall effect sensor for angular measurement and electromyography (EMG) sensors for muscle activity acquisition within a microcontroller-based architecture. A gait experiment over a complete cycle was conducted to evaluate system performance, focusing on the biceps femoris and rectus femoris muscles. The obtained EMG signals exhibited activation patterns consistent with physiological expectations: increased biceps femoris activity during the swing phase and peak rectus femoris activation during the stance phase. Additionally, the device measured knee joint angles within a range of 0° to 65°, achieving a Mean Absolute Error (MAE) of 2° compared to conventional goniometry and a Mean Absolute Deviation (MAD) of 3.09°. These results validate the accuracy and reliability of the proposed system for capturing synchronized neuromuscular and kinematic data. The device offers a portable, low-cost, and user-friendly solution with potential applications in clinical gait assessment, rehabilitation monitoring, and biomechanical analysis.