Reverse animation in Matinee

Hi. I want to use Matinee to make a quite simple animation of a character consisting in a moment idle, a step forward, a moment idle and an step back.

I am using Mixamo animations; mixamo_idle for the character to stand still and mixamo_walk to step forward. Everything is all right up to that point.

The problem arises when I want to use the mixamo_walk animation to step backward (playing it reverse). I can slow it down or make it play faster (editing it in the timeline by using the the Ctrl key) . but i can not find the way to play it backwards.

Any help?