*cue CER1389 sitting on her chair pretending it's a icelandic, trying to make it tolt*
Tolt is all about the horse coming through from behind, moving forward and coming 'up' infront. So it starts with collection. I'm going to explain the very exaggerated aids, the ones for learning it, or possibly teaching a horse to tolt. I liken it to teaching a rider to canter. When they first learn they are taught it in an exaggerated manner, then, as they progress, their aids are far more subtle.
Rider sits up nice and tall, pushs weight down into heels, closes thigh around and holds in with seat bone and abdominal muscles. Horse begins to slow its walk. Rider shortens reins, sits even deeper, raises hands. Horse starts to bring it's front end up. Rider closes thighs around and squeeze (with thigh, not lower leg). Horse tolts. Often the rider will be carrying a schooling whip, and a slight flick is given, to get the back end to come through.
This aid is very much dependent on the horse in question, however in tolt the riders lower leg rarely touches the horses side (infact this is common in all icelandic riding, the lower leg rarely touches) and it is all cued from seat aids. The shortened reins and raised hands are more to encourage the front end up, never to hold it up.
Showing the riders legs not touching the horses side - and I think it shows how much his seat is being used. If you look at his amusing facial expression, it is because he is making a "kissing" noise. A lot of icelandics are trained to this sound being their cue to tolt.
With a natural tolter, it can be held from the seat so much so that there is a "loose rein tolt" class. In which the riders have to tolt "showing no contact between riders hands and horses mouth" for this, most riders will put one hand on the buckle of the reins, and drop the other hand. Although this looks effortless, it is all held from the seat still.
Although (the dun) looks effortless, I guarentee it's not. I have been lucky enough to ride this horse, and attempt loose rein tolt on him. He naturally tolts in hand, not trots, however after loose rein tolting him for about 10 seconds I had to stop, and when I dismounted it felt like I had done 90 sit ups! I found I had abdominal muscles I never knew existed!
*CER1389 runs for cover under desk, donning a tin hat for protection*