In this work a model is presented that can improve the estimation of muscle activation under electrical stimula-tion. The model includes not only the motor recruitment but also the H-reflex recruitment, which is, at the lower stimulation levels, responsible for a larger exerted force than expected based on only motor recruitment. In the model it is assumed that recruitment curves are sigmoid shapes, that there is no difference between motor units and no specific recruitment order. The model is fitted to the measured recruitment curves of two healthy subjects and shows good fits, with R2 values above or around 0.95. The next goal is to use this improved activation model in combination with a force estimating muscle model in order to enhance the accuracy of the force estimation.