I'm presuming you mean trotting.
When you ask to come back to the trot think up and back, let me break that down. You're forward and pushing in the extension, then you want to keep that, but compress it, so we want the horse to have more up than forward and back as in we want the haunches under the body slowing the horse down while still pushing.
Imagine if you were extending the trot/jog and then you asked for a rein back, the horse would curl his haunches, sit back and do the reinback. So that's basically what you want but then before the horse actually broke from the trot, you asked for more forward, but by then you've taken the forward push away and you're left with the up push.
Does that even make sense?