This paper presents a low-cost rehabilitation support system for lower extremity muscle strengthening exercises: LOWER-LIMB FOLLOW-UP. The system includes two main modules: a goal-oriented serious computer game module for the patients and another that provides feedback to the physiotherapist. By analyzing the surface electromyography signals obtained from the relevant muscles of the patient, it is ensured that the patient gains points in serious computer game. The raw surface electromyography signals generated while playing the games and the result of the signal analysis are saved in the database. Feature extraction methods are used for the electromyography signal analysis. The physiotherapists can access the database via a web-based application and obtain information about their patients' performance. Muscle strengthening exercises frequently recommended, such as active knee extension exercise for quadriceps, active knee flexion exercise for hamstring and terminal extension exercise for vastus medialis obliquus muscle groups, are selected for this study.