I've had a couple of people ask me recently about how to get the horse stretching. I want to state up front that if you're just introducing a horse to stretching, they won't get to where Soon is right now immediately. It will take several weeks to get a horse to develop a good stretch, and upwards of a year or more from there to really put a complete topline on the horse. Thus, my first tip is patience. Don't rush, and try not to get frustrated with slow progress. Learn to feel the little "ah-ha!" moments your horse has when they start to understand and offer you what you're looking for, even if it's just for a stride or two. Build off those moments, and your patience and dedication will be rewarded.
Introducing the Contact - Pressure and Release
Each horse is different and you have to find what works best for your horse, so here are a couple of tricks I know.
I teach my horses with the use of lateral flexion. I tried to find a good video on YouTube to demonstrate, but they were all either about "The Method©," or they were set to the Lion King soundtrack (seriously!?) and all about nature and hugging and crap. This is NOT an exercise in cranking the horse's head around and twisting the neck. So we'll just skip that garbage and get to the point: pressure and release. Horses learn and respond to the application and release of pressure. All good riding or handling is, is the understanding of how to apply pressure, and when to release it to shape the horse's behavior. I use lateral flexion not necessarily to get to longitudinal flexion (in the poll), but rather to teach the horse to yield to the pressure and seek the contact with the bit. The longitudinal flexion comes later as we develop the stretch with an engaged hind end.
The lateral flexion I introduce on the ground (in hand) and then I work on it while mounted. Here's the scenario mounted: stand and let the reins go slack, then pick up one rein and bring your hand over to your knee. Ask the horse to flex gently to that side with pressure on the rein and a gentle squeeze of the leg on the same side (inside leg). Keep asking until the horse softens and brings its nose over to that side. If he's pulling/resisting, don't let go until he softens. As soon as he softens, even if it's very slight at first, give him your hand and allow him to return. You're trying to teach him that when he yields, he gets rewarded with release. DO NOT grab a hold and ask for more and more flexion - that is uncomfortable and confusing for the horse, and entirely unproductive. You do not and should not have to bring the horse's head very far around, only enough to ask him to yield. Always release when he yields. He should start to understand fairly quickly that yielding to pressure = release. Give him a second to think about it between each one when he's good. Repeat equally on the other side; you may find he flexes better one way than the other. If he wants to move the hind end away, allow him to, but don't let it turn into a spin because that's also not the point. If it gets to that point, then you need to take it back a few steps and simplify, because that's a sign he's not understanding or getting frustrated. Once he flexes and is understanding the yield part, you can add forward movement to the equation and start to bridge some concepts.
Introducing the Stretch - Forward Stretch
So getting into the riding part finally, the lateral flexion exercise above transitions into forward riding when you start on a 10 or 15 meter circle. You're basically replicating the in hand video above from a mounted position: you have a soft, elastic connection with the outside rein and an open inside rein. Even contact on both reins. Outside leg is supporting just behind the girth. Gently apply the inside leg (think inside leg to outside rein) and ask him to bring that nose in and down as he steps forward. If necessary, give the inside rein a gentle squeeze. Once he yields (even slightly), soften your inside hand to reward/release. Again, you may only get a step or two starting off, but after a couple of sessions you should start to see him wanting to stretch forward and down, with his nose on the vertical or poked out slightly (this is not an exercise in cranking the horse's nose to its chest). Continue until you get some pretty consistent stretching at the walk, and be sure to not drop the outside rein and allow the horse to bulge through that outside shoulder. Once the walk is established, you can try it at the trot. The outside rein is very important as you don't want the horse to just
flex to the inside and throw the outside shoulder. It's very important
they be on the contact and take the stretch down, versus being on a long
rein and expecting them to find the contact. The above techniques and explanation help set the horse up for what ultimately works best for developing the stretch, which is explained below.
Riding the Stretch - Encouraging Contact
Regardless of which of the above techniques you use to introduce the beginning concept to the horse, once you get him starting to comprehend seeking the contact, it gets a little simpler. I go back to the George Morris videos from the 2014 Horsemastership Clinic on USEF Network - watch the flat sessions, and you'll notice getting a horse to soften is really just closing the fingers and closing your leg. Watch the Day 1/Group 1 flat session at about the 35 minute mark when GM gets on the horse (whole session is great, but when he's on the horse is where you see the demonstration). Watch and listen. If the horse's head goes up to evade the contact, your hands go up. Never lower and widen your hands to get a horse's head down. Hands travel up and maintain that straight line from elbow to bit. Close your fingers on the reins and gently enforce the contact, and push from your leg up into it. Make it slightly uncomfortable, or more work, for the horse to be up and running around like a giraffe. Horses will eventually come down and soften. Once they do, offer your hand by lowering it as they lower their head (maintaining straight line elbow to bit), and soften the elbow to allow them to continue the stretch. Don't throw the reins away when they yield and start to come down. Just soften your arm and allow him to bring your hand forward/down with him as he travels down in the stretch. He should not be pulling or leaning. When he starts getting really deep, then allow him to take some of the rein, but again, never just throw a bunch of rein at him because then you lose the connection front-to-back. Let him take what he needs and maintain a feel of the mouth. Like Mr. Morris says, impulsion first, but the secret is to give with the hand. Flexion at the poll is secondary to activity and flexion in the joints (hocks) behind. Seriously watch the whole flat session, because it's a wealth of information no matter your discipline!
It's important to emphasize your legs are just as important as your hands. You have to keep encouraging her to be active behind. Learn to feel when the hind leg is in the air, because that is when you apply the pressure with your leg on that side to get the hind leg to step under (for example: at the walk, when you feel the barrel swing to your right, the left hind is in the air. You want to apply your left leg when you feel the barrel swinging right, because your left leg cues her left hind to step bigger. Alternate pressure like that to encourage a bigger walk). A horse cannot correctly stretch, or correctly be on the bit at all on any length of rein, if the hind end is not first active.
Some horses just need the "close the fingers, leg to hand" part to understand stretching, but for those that don't get it, the in hand and lateral flexion exercises help bridge that gap of pressure/release. Hands should be very quiet. You don't have to have really wide/low hands to make this work; as you can see in the video my hands don't move very much, and I like to think I (for the most part with some exceptions) maintain that straight line from elbow to bit. That is very important - no puppy dog hands or broken over wrists. Carry your hands, elbows in, and relax your upper arm. Your elbow is the hinge, and that needs to be loose so you can communicate effectively. Keep your hands quiet and stable, because if you are constantly wiggling fingers and the bit, the horse has nothing to really seek if the bit's constantly moving around in the mouth. The legs create the forward energy, and the hands receive it. Think of it that way in terms of how to ride your horse forward into the bridle, versus pulling him into it, which is of course incorrect. No need to be "handsy," but you do have to explain to him what it is you really want him to do, so hopefully the above information helps out. If you have any questions let me know as I'm happy to discuss!