...The practice of dressage as a method of training a horse and developing it's flexibility, responsiveness, balance and strength are so basic that the movements are used as an integral part of riding in many disciplines...
Horses were able to be flexible, responsive and balanced for a few thousand years before dressage was invented. That is because any decent rider values a flexible, responsive and balanced horse. But developing flexibility, balance, strength and responsiveness is done by good riding. Someone riding a forward seat can teach all of those, without ever looking at or caring about the dressage scale of training.
Heck, I've done it, and I'm hardly an experienced rider or trainer. How? By riding in situations that require the horse to respond with balance, strength, etc. Riding thru washes filled with sand, up short hills, down short hills, on ATV trails filled with gullies and very irregular terrain forces the horse to learn balance, and to gain strength. Riding a horse thru turns, and increasing either the speed of the turns or the tightness or both teaches flexibility and collection, since a horse cannot power thru a turn with a stiff back. You use the TURN to create FLEXIBILITY, and also...well, TURNS!
Mia has a very unbalanced canter, but it has improved greatly. How? By cantering. She would put her head inches off the ground while going full speed, so I braced my thighs against the pulleys (love Australian saddles!) and pull her head up. Right now, she is cantering with her head too high, but the cure for that is more cantering, and doing it until she is tired. Trooper had a pee-poor canter when we started, but he now has a nice, medium level collected canter - because we practiced it, and practiced cantering in turns.
...a very minor example would be when I used to ride a trail horse who was frequently tripping. He was a western horse who had never been ridden on contact before and basically allowed to move just as he pleased, which was very lazily, and thus he stumbled a lot. I found that by taking up some contact, asking him to soften to the bit and step further under himself (I would ask for more energy from behind but use the contact to encourage him to step deeper rather than just fall out faster and harder onto the front) he began to trip less often.
I will admit, I've often wondered what it would be like to ride a lazy horse! Maybe someday I can borrow one and find out. If I had a horse who stumbled a lot (golly, I do...Mia), then I'd take her out on increasingly rough trails. Horses don't enjoy stumbling, so she would have to (and has) learn to watch her footing AND to lift her feet higher. She used to stumble bad when cantering...some scary times, when a horse is WAY forward and stumbles...but she is much better now. Not because I ride her with contact on the bit, but because she has been on uneven trails and decided stumbling hurts, and because I've lifted her head by brute force while cantering until she figured out it feels better that way.
Collection doesn't prevent stumbling. More energy might - like I said, I've never had a problem getting Mia energized! I'm glad what you tried worked for you. Millions of horses are ridden 'on the bit', and it works great for them. So it cannot be 'wrong'. But neither is it 'right', because millions of horses have also been ridden successfully and long 'off the bit'.
Sure, it's not formal dressage, but it is utilizing a dressage type of contact with impulsion into the contact to change a flat, forward energy into a more vertical energy (for carrying the rider). It's so rock bottom I am not sure you'd call it dressage, but it requires the horse to work a bit harder but should make him carry the rider better, which is thought to prolong his useful lifespan.
But that "dressage type of contact with impulsion into the contact" has not ever been shown to make a horse carry riders better or prolong the useful riding lifespan.
I just got back from a jog. I jog on some of the same trails I take Mia on. Like a horse, my goal is efficiency. I don't leap. I don't take shorter strides, and use more power from my hindquarters (so to speak) to lift my body higher into the air. I just cover the ground as efficiently as I can. And that stride is learned by having done it a lot. If I had a pack on my back, I would do the same thing. Human studies show people respond to the weight the way horses do. We change our stride length, the duration our foot is on the ground, and we do it without conscious thought. Maybe not the first time we carry a backpack, but we don't have to carry them long to figure it out - without thinking.
How do you train a horse to decrease the pressure on its joints and legs caused by the rider's weight? You do not. Until recently, we didn't even know how they did it. Yet they have done it for thousands of years.
'On the bit' is an interesting term. I prefer 'on the aids', and I consider that to be a horse who is listening to me and responding to my cues. When we neck rein, my horse is 'on the rein'. When the horse slows from my seat cue, he is 'on the butt', and I guess when Mia accelerates when I make kissing noises, she is 'on my mouth'. I would argue all those come under 'on the aids', but I'm not using the bit to do it. I guess I consider 'on the bit, reins, butt and mouth' to be 'proper' riding, because it means my horse is paying attention to me and responding to my goals.
For backing up properly, I consider that to be...well, backing up. Quickly. Efficiently. Oddly enough, that was probably the ONLY thing Mia was good at when I first got her. She might have been uncertain about a trot, but she would back up 50 yards with enthusiasm!
Did she "flex at the poll, lift the base of the neck and bring the feet backward by lifting them and carrying them back"? Beats me, but she sure shot back fast and straight!
This brings up the stiff back/round back puzzle. Does a horse need to 'round its back' to back up well, or to go around a bend or to do an in place 180? The backbone has limited movement, and it doesn't ever 'round up' under the rider outside of a rodeo. The horse protects its back, and one way to prevent excessive movement in the back is to stiffen it. That honestly works well enough for backing up and for in place 180s. I've done enough spins with Mia where her back was stiff to know she can do a lightning fast in place 180 without rounding her back. For powering around a turn, what is needed is not a vertically round back, but some horizontal flexing and differential power from the legs.
"The race horse engages the hind legs more forward under his body than the dressage horse. Such engagement is definitively helped by the longitudinal flexion of the thoracolumbar spine and dorso-ventral rotation of the pelvis and sacrum around the lumbo-sacral junction, which is all natural at the canter. However, the race horse does not utilize greater engagement of the hind legs to enhance balance. Instead, the race horse utilizes the elastic strain energy accumulated during the decelerating phase to maximize the propulsive action.
The horse’s morphology also does influence the position of the hind hoof under the body at impact. For instance, two horses working with the same thoracolumbar column and pelvis rotation; a horse with a sickle hock will place the hind hoof more forward while a horse with a straight hock will place the hind hoof less forward. Forcing a straight-legged horse to track up deeply, would place the horse at risk of hock injury as well as sacroiliac problems and/or stifle issues.
" Hind Legs Engagement and Stifle Problem
As a practical matter, to teach Trooper to power thru a turn, I rode him thru turns. I did circles with him. I tightened the circles. I used my balance to shift weight to the rear, tipped his nose in (that was when I began using a bit with Trooper) and tried to help him flex thru the turn. After a bit, he started doing it on his own because it felt better. Mia & I are now working on that during our arena days. She is a stiffer horse, so it will take her longer. Maybe a dressage rider would use the same tactics. I don't know. I won't use lunging or side reins. Not because they are bad things, but because I don't know how to use them. So we'll just work on turns until her turns get better.
But her turns WILL use a natural head carriage. She will not have a bit guiding her forever. Trooper can do it now without using the bit because he learned how to carry himself. That is my goal for Mia. It is not right or wrong. Dressage horses are not ridden wrong. Neither is a loose-rein western horse. The approaches differ, but both, if done right, result in a balanced, flexible, strong horse moving comfortably and willingly. Of course, if the goal is a collected gait, then you need to follow dressage principles. But you can get a relaxed, strong, balanced, flexible horse capable of carrying a rider well for many years without using dressage...