In this paper, we present a method for emulating human walking motions with leg impairments or disabilities using humanoid robots. Our optimal dynamic multi-contact motion software generates the emulated motions. We take into account the full-body dynamic model of the robot and consider possible leg impairments as additional physical constraints in the optimization problem. The proposed approach is verified using HRP-2 humanoid robot. Simulations and experiments revealed extra energy consumption when constraints translating impairments are added, which is assessed using an infrared camera. Our research is the first step toward potential usage of humanoid robots in human-centric studies, diagnosis of human disabled motions, as well as an active mannequin for welfare instrument evaluation.