I am currently working with a student with precisely the same challenge being discussed. Far too many years of this brave, intelligent, and capable young woman being allowed, even taught to use force to make a horse do something, but too small herself to win and riding a horse that gradually learned from her and other students to fight back.
Now I have her on a very well trained but also roughly ridden horse (by many different riders) of good size, and Anglo Arabian, and she get's to see and learn the difference.
Now and then when her form breaks down, and she loses her center this horse, cabable of floating like an angel, will throw his nose up and start stiffening up, hollow back, forehand drilling into the ground, dragging hind quarters, etc. And as I put her back together by coaching the correct forms, sequences, and especially the power in softness and releases she can feel him changing under her ... going back into his lovely collection and suspension in all gaits.
I see that rein releases, while I've worked to develop them into an art form, have a counter part in the use of any aids, natural or artificial. Teaching my students how to "ask," and then say "thank you," even before the horse decides to agree, has a wonderful effect on the relationship of the horse to the handler. Horse's I use for students love to come to me for conferences. I discuss with the horse the events just happening and how we might help the rider hear what we are telling them when we go stiff and bouncy and drop out shoulder on turns or out whole forehand when our back, neck, and mouth or nose are hurt.
The student hears, of course.
I am so proud of this particular young lady. Though we are working together in what she thinks is conventional horse handling methods she is learning "the ask," replacing the demand. She is learning the greater importance of the thank you than the request. What others' call the release (as in pressure release) I refer to as showing respect by having good horse manners.
I use word pictures to get the point across. I'll mention that horses, when they put pressure on another horse often let off the pressure long before the other horse conceeds or complies. Bared teeth and snaky head rarely go so far as an actual bit. Same with the kick - it's usually never delivered. And when I have an itch, as a horse (but of course as a human too LOL) all I need do is point to that same spot on the other horse to get him started scratching me with his teeth.
I ask, with students who have the habit of pulling and forcing, to come up with as many ways as they can demonsrate throwing the reins away. The object is to ask by other means, but of course including actually dropping the reins.
She's inadvertently caused this wonderful horse to "stick," over downward transitions including halts. Today we had to go back and do that lesson again. Namely: you do not stop a horse with force, you stop him with asking and thank you.
Asking, of course is to stop moving your center forward, to relax downward, to breath out more than in on each breath, (that tiny moment when you push that last bit of breath out is something the horse feels very strongly as a message from you of confidence and relaxation and they wish it too for themselves, so drop their energy downward as well). Then you drop the reins.
It would seem counter intuitive - drop the reins before the horse has even slowed? Yes. You can always pick them up again, cue softly, remembering ALL the aids one can use for downward transitioning, and drop those reins again.
In five minutes he was back to the level I had trained him to with her as rider some months ago ... from going on and on around the riding hall not slowing at all, pushing out and against the bit (blasted things) with the corners of his mouth to save the bars, to quietly coming to a halt with the reins laying on his neck for the last three or four strides.
I'm still working on other things he does out of being a lesson and loan horse for too long. But he loves it when the rider is gentle with him, and polite. He has a good sense of humor, loves to fake biting, but never bites, wants to help in every way (you should see him try to help put the saddle on - it's a riot), and like all horses deserves respect and good manners from humans.
And he knows how to ask for it and teach the rider - at least the ones that listen carefully as I act as his translator. "He's now, by going to that nose up hard bouncing jarring trot, telling you that you are coming down on his kidneys and yanking the bit - please get over your center, reach down to the ground with your legs and anchor your little fingers to his withers so your hands stop bobbling." There is almost an instant shift in him to smooth suspension, lovely soft collection, a Ramener with out use of the bit, and energetic reaching under with his hind quarters.
It's so dramatic the rider cannot miss it. And if the rider is as patient and commited as the horse they will learn to find it again, just as the horse teaches it.
Thank you for the inspiration to tell this little story, and to speak once again about the polite hand, and the rein that is in release far more than in ask - the path to bitless and especially bridleless riding. I believe this student will reach that level soon.
And of course I do it now with her on the lunge line and will continue - though probably not for five years.