Although predictive forward gait simulators have existed for a little while, only few sensitivity studies have been proposed. We present a study analysing precision, accuracy, stability and sensitivity of such simulator. We studied a gait simulator based on the trajectory mimicking method proposed by Lee et al. [1]. We assessed the effect of motion variation on the resulting gait simulation using the sensitivity analysis method proposed by Saltelli et al. [2]. Our method supports the use of this simulator for prediction.