The design, realization and verification of a system for personalized rehabilitation of Spinal Cord Injury (SCI) patients are here presented. It consists of two main parts: (i) one induces in the patient the physiotherapic movement proposed by the trainer with Functional Electrical Stimulation (FES) and (ii) the other integrates a muscle fatigue feedback evaluator based on acustic principle by wearable microphone. The importance of this fatigue feedback is crucial since SCI patients are unable to feel muscle soreness, which is an important parameter in FES rehabilitation. Indeed, the efficacy of this treatment is limited by the capacity of the muscle fibers to carry out the induced task. To optimize the feedback module, the performance of two different condenser microphones (analogic and digital) were compared each other as well as with the traditional method based on Electromyogram (EMG). Among these techniques, it was found that the digital microphone provides the best performance in fatigue estimation over time.