Mathematical models of the skeletal muscle can support the development of neuroprotheses to restore functional movements in individuals with motor deficiencies by the mean of Functional Electrical Stimulation (FES). Since many years, numerous skeletal muscle models have been proposed to express the relationship between muscle activation and generated force. One of them (Makssoud et al [2]-[3]), integrates the Hill model [5] and the physiological one based on Huxley work [4] allowing the muscle activation under FES. We propose in this paper an improvement of this model by modifying the activation part. These improvements are highlighted through the HuMAnS toolbox [1] using a 3D biomechanical model of human named Human 36. This article describes this toolbox and the software implementation of the model. Then, we present the results of the simulation.