In this paper we present a preliminary study of the impact of avatar realism on illusion of virtual body ownership (IVBO), when using a full body virtual mirror for fitness training. We evaluated three main types of user representation: realistic and non-realistic avatars as well as no avatar at all. Our results revealed that same-gender realistic human avatar elicited a slightly higher level of illusion and performance. However qualitative analysis of open questions revealed that the feeling of power was higher with non-realistic strong-looking avatars.