Triggering the Hollowing Reflex
Just like pulling the reins down along the sides of the shoulders on a stargazing horse will not help the outline, the horse's first natural instinct is to fight the pull form the drawreins, pulling down on his mouth. What the regular reins are supposed to do is not place the head down, but merely relax the jaw and tongue so that the horse will stretch the rein. The horse is the one lowering, not the rider or the gadget!

The short drawrein will do exactly the same as the underline muscles during rollkur work - they will shorten the underline and pull on the nuchal ligament to be wrapped around the spinal column lengthwise, and compress it. The bottom of the S-curve will push out, and the horse will hollow. Added to this, the exaggerated pressure on the tounge will cause stiffness in the jaw and poll, which will tense the topline in the same way as a stargazing horse tenses his topline. Wether the horse actually holds his head way up, or is striving to move his head upwards but stopped by the drawreins, it's all the same. The same hollowing reflex is at work.
Rubberband Neck Extender

This device is a mechanical drawrein that is not directly adjustable during riding. It goes from the girth area through the bit rings to the poll. It never reaches the hands, and the distance from hands to head has no impact on the horse's mouth. It is also elasctic, and can thus invite the horse to take contact. It's biggest drawback is that it is not adjustable from the riders point of view, so the rider cannot give, to reward the horse, or allow a full stretch. This is quite inflexible, and does not teach the horse much other than to lower his head. It relieves the rider from the task of holding and organizing the drawreins, but this only inclines even poorer riders to use them. The fact that there's no connection to anything at the withers, such as hands or surcingle, speaks for them. The fact that they are mechanical and not something a skillful rider can use in his conversation with the horse speaks against them.

The distance where the rubberband is taut can be stretched and elongated some, and the horse can actually stretch forward-down and outish. That is, if you don't adjust them too tightly before getting on. And being loosely enough adjusted, this device will not prevent a stubborn horse from shortening his neck and inverting totally. And the only use left in defence of this thing, is the fact that the horse can use it to quiet the bit from rattling in his mouth, because the rider has unsteady hands. A hard, steady pull is at least less unpleasant to the horse than hard snatches on the reins, going from slack to taut, to slack, to taut. The horse can lower the head and steady the bit against the elasticity of the rubber band.
Sidereins


At the Spanish Riding School, tradition has it that sidereins have always been used for lungeing and to a certain extent for long reining. How and why they do so is out of my sphere of knowledge since I did not attend the school, so I will not go into it. But for those of us not attending the school, this is really nothing to much consider using for any purpose. Instead of lunging endlessly with sidereins, having a horse that fights the sidereins or goes behind the vertical/bit, or as is most common - learns to hang on it to make it stop bouncing the bit in his mouth, time is wiser spent trying to learn long-reining, or simple work in-hand. Most riders can accomplish a lot more with only a bridle on working their horses in hand with their feet on a track 3 feet to the inside of the horse's track, working the horse by bending and stretching at the walk. Bending and shoulder-in at walk is often more useful than trotting in sidereins.

Some users say they must longe in sidereins to get straightness. They adjust the inside rein shorter to get the right bend on the circle, and then they longe. But the sidereins do not sit on the horse. They cannot feel the straightness/crookedness of the horse, nor can they drive on either side with the legs or release to get a stretch. They can only fix the head. I see so many horses lunged in sidereins that are overbent to the inside, push the shoulders to the outside and set the haunches on a track inside of the forelegs. That's a blueprint for crookedness.
Stop fixing the horse's head into positions! Learn to do the Shoulder-In Volte in hand, then to longrein, and ride the horse to get rhythm, relaxation, contact and schwung as a riding horse before you work on straightness. Straightness cannot be found in a position that you can adjust with straps any more than "on the bit" can be found in strapping the head down.
Sidereins are as inanimate a gadget as anything else, and does not improve the stretching forward-down-out but rather teaches the horse to keep the shape of the neck and jowl and drop from the withers. This is NO STRETCH!
The sidereins fix the distance between the horse's mouth and and a point on the girth or roller. The horse can handle that in many ways, by shortening the neck, by curling down, etc. To make a horse go "on the bit" in sidereins, you need to be expert in driving it forward just so on the lunge, you have to release him often to save him from cramps that cause resistances, and have the horse quite well schooled. So what's then the point, if you have a well-schooled horse and know how to drive correctly? If you can do that, you can longrein successfully, too! Or why not ride?

The horse in the picture is well schooled. He is in sidereins that appear way too short for any productive work. In walk he is overbent and curling in. When he arches the neck upwards enough to piaffe, although this piaffe is not engaged enough, the hindleg is raised higher than the foreleg, the reins are of adequate length (although one would wish for a longer neck). So using this for short bursts of work on extremely collected exercises has some kind of purpose. But they can equally well teach the horse to curl behind the contact.

Simply using them for shortening the horse is counter-productive, since the horse soon learns to stiffen against the mechanical non-yielding lines attached to the bit, and thus learns to resist.
Sidereins also block the head and neck movements of walk and canter gaits, which leaves trot as the only option. In trot, with its sometimes rather jarring up and down movement, the straps and rubber doughnuts, weighing considerably more than the desired "weight in the reins", jerk up and down with the gait. The only thing that helps the horse evade this rather unpleasant effect on the bit is to heavily lean onto it.

There's also the problem of the horse stumbling, losing balance, being frisky on the lunge line. And what happens? The fixed leather siderein will snatch the horse in the mouth as hard as he moves his head. This RUINS the mouth of the horse, and makes him utterly insensitive. The possible benefits you can have from sidereins are overshadowed by the fact that they harden the mouth in many intricate ways.
Some say the horse can learn "proper contact" with sidereins. I guess that depends on what you mean by "proper contact". If you mean that the rider should be able to hold the reins at a fixed length for lengthy periods of time, and that the horse has to be the one who adjusts to it all the time, then the horse can learn that from sidereins. If "proper contact" means that the horse always tries to stretch the reins, and that the rider adjusts the length to suit the activity of the back and hindquarters, to reward or bend, and places the head higher and lower with the same amount of rein traction, then the horse will only learn from the sidereins not to mess with the hands.
Sidereins also cannot position the horse at the poll, or rather the C1/C2 joint. You can buckle one siderein shorter than the other, but lunging, you have no control over whether the horse bends off at the shoulders, mid neck or at the correct spot.
No control, is actually the theme of sidereins. You can't control their length from the end of the lunge line, you can't control the horse's shoulder, or bend. You can't release, or even shorten momentarily. So why use them? So unless you attach them to a cavesson and take care to chose the lightest doughnuts, release them frequently, drive carefully, leave them.
Thiedemann Reins

Thiedemann reins are semi-drawreins which the unskilled rider can use without actually having to hold the extra straps in the hands. Some riders praise these contraptions and call them horse friendly and the best thing since sliced bread. I have even ridden for instructors who insisted I use them before they had even seen me ride, meaning they go on her horses by default. Oh dear!
But some argue they are kind. They only apply until the horse has the head set, and then they automatically relax. These advocates probably love drawreins for the same reason, the head set, but are not dexterous enough to use them. These advocates don't realise that the proper head carriage is not achieved by pulling the bit downwards until proper position is taken (the head set). Proper head carriage is achieved by activation from behind which results in the back and the base of the neck lifting, the neck arching and all things perfect.

So why the reins at all!? Why don't riders ride without reins if that's so damn correct. Well... Before "all things perfect" in the sentence above comes "the poll relaxes and drops the head to near vertical by the action of the bit on the jaw". This is what the hands do, in the case of "on the bit" and front end poise. They ask "Please relax your jaw, please position at the poll, please elongate the neck, for I will give you plenty of rein if you do it."
This must be possible whereever the horse has his head. That's why we ride with adjustable reins in the hands and not sidereins. High or low, in, down or out, you must be able to feel the mouth of the horse, and quickly ask it to relax if clenched. Is this done by set-length reins pulling the bit down until you have exactly the same head position every time? No, that is automating the head set.
Thiedemann reins and metal loops for adjusting them also add weight to the reins. These unskilled riders are not only heading for a head set and a tense neck, their reins also flap and flop by their sheer weight, jerking the horse in the mouth.
The Rein-Aid Inserts

These are basically short extensions of the reins that have been intersected by a piece of elastic. Or, intersected may be the wrong word. The firm leather rein is looped in the background, and the elastic stretches between this leather rein looping (slight tension on reins) and the elastic being stretched out so that the firm leather rein is taut (quite firm rein tension). There may be somewhere around 1-2 inches of "give" in these things.
I'm not going to barf all over this stuff. They're OK, especially from the horse's point of view. They are used by riders who are unable to have an elastic, living contact coming from the feel in their hands and relaxation. Those whose hands are not independent of the horse's movements, and thus the rider's own seat. These people know that, hopefully. They just use them to help their horses.
What they will not help in the long run, is the problem itself. If you use these inserts, they will do the elasticity for you, and you will only reinforce by habit that a tense grip on the reins is OK, and the subsequent bobbing of the hands is OK, since the rein-aids soften it before it reaches the mouth. You will never learn to feel the soft chewing of the horse being on the bit.
Chambon & De Gogue...

Recently, in the perspective of dressage, inventions and developments have been made to the drawrein. The idea has been to actually achieve the gradual release that is needed to encourage the horse to stretch forward-down-out for the bit. They are quite more elaborate than the drawrein, and function by tackle action. These are really lunging devices, much the same as the traditional sidereins are used at the Spanish Riding School, but many people use them for schooling and riding in general. I personally find it incomprehensible, that riders think themselves less equipped for making the horse stretch forward-down-out from straightening, driving and rein manipulations, than a simple string that gives mechanically at the right angle. I mean, they seem to have no problem with the fact that this effect is created by something which affects only the head of the horse, so it's not a noveau "Look, Mama, no hands!" kind of thing. It's "Look, Mama, this string can do what I can't!" One can only hope that these rides realise their need for further education and the danger in thinking that an auxiliary rein can ride for you. A couple of tied knots on a string will not cure neither a painful back nor poor education.

Out of all of them, the chambon is the only one which really works satisfactorily in its true context - lungeing. The chambon is the only device that lets the horse stretch fully forward-down-OUT.
The Chambon is really a simple thing. You could make it yourself if it wasn't for it being so cheap that it's less expensive to buy the finished product, than buying leather straps, rings and a string. You need a girth for attaching the main strap (blue) to, and if you don't have a lungeing girth, use your saddle and its girth. Next, there's a short strap (green) across the crown piece of the bridle (that you really need to have on). There's a ring (yellow) at each end of the crown piece, through which the string (red) runs from the attachment to the bit.

The function is as such:
As the horse lifts his head and pokes his nose, tensing his back, the device applies because the strings are pulled taut. The distance to the raised head (poll) becomes longer than in a relaxed state, and the poking nose uses up its share of the string as well. So the string pulls on the mouth, but not only that. It presses the crown piece down. Any attempt in the right direction is rewarded instantly. If the nose is dropped there is a release, and especially, if the poll is lowered there is a release. In a full stretch forward-down-out the distance from girth to poll to mouth is still shorter than when the horse has inverted. The device is slack.

Horses usually don't even initially fight this device, because its action is quite soft. Compared with a Harbridge or a standing martingale which the horse can have slack, and then as he raises his head it can snatch taut, and cause panic or fits. I have personally seen a horse and rider topple over because of a harbridge. The horse got upset by something and threw her head up, so that the harbridge snatched at ther mouth. From this she paniced and started fighting it, which resulted in her rearing and toppling over.
The 2 Part Chambon Lunge Device

If you necessarily need to use something to get your horse to stretch down, please use a kinder and cheaper gadget than the Pessoa System or The Abbot Davies. Remember that patent holders make mega-bucks out of your desperation, and sell a bunch of strings for $150 or more. The money you spend will not do your horse any good. Construct a cheap and kind homemade thing instead, and spend the money on a chiro for your horse, or longlining lessons.

Use a chambon in front and simply sling a rubber neck-extender around the hocks and attach to the girth on both sides. I guarantee the horse will feel just as much behind is rear end, but the chambon will have mercy on his mouth and allow him to stretch all the way forward-down-out!
Remember also, that it is the innate drive forward from the hindquarters that create the stretch, so teach your horse to drive forward without rushing.
The Pessoa System

During the Pessoas' total reign in showjumping in the 80's and 90's many "inventions" came from their barn. One was the Pessoa Gag Bit, which I speak of elsewhere, which is a combination of a driving bit and an elevator gag, and then the Pessoa Training System used for lungeing. This system is supposed to get the horse to stretch down AND engage the hindlegs forward, and thus be good for the back. I have seen it at work several times, and whilst it does get the horse to lower his head on the lunge, the most glaring effect of this contraption is that it succeeds in jabbing the horse in the mouth with each push of the hindlegs.

It has a semi-intricate pulley system that via a lunge-girth connects the gaskins with the mouth. I guess the rope is supposed to encourage the horse to grasp forward with the hindlegs as it tightens around the hindleg and at the same time limit the height of the head. But which is more sensitive - the skin on the hocks or the mouth!? The horse will be encouraged to roll down but not stretch to the bit, because the bit jabs at the mouth with each step. Now this is mechanical if anything!

I have also never seen any horse truly engage in this "system", only go on the forehand and curl behind the bit. It can be adjusted lower (for more stretch) and higher (for collection) but it seems to have very little such effect.
The Hock Hobbles

Some of these devices seem to be so ignorant of the horses mouth, that I simply cannot think they are. It must certainly be intentional to jerk the horse in the mouth, if you use something called hock hobbles to connect the hocks to the bit. Now, this is apparently some kind of western training gadget, but it's worth mentioning, because it sooner or later seeps into mainstream riding, anyway.
The Abbot-Davies Balancing Rein

Another version is the Abbot-Davies Balancing Rein, which connects the bit to the tail of the horse. I don't know if anyone uses this kind of contraption, at least not whenever they can be seen by someone. It is in practice a standing martingale that pulls the tail in between the buttocks. One might think that the horse would tuck his croup from the pull on the tail in between his hindlegs, but I hardly think so. A horse must be driven to place his hindlegs further underneath himself in course to tuck the croup. And the most impact will still be on the mouth, when the entire weight of the straps under the belly flap with each step. Also, it does not allow for the neck to stretch forward-down-out, only to curl towards the knees.
The "Cowboy Dressage" Tie-Down Device

Eitan Beth Halachmy calls his kind of horsemanship "Cowboy Dressage" because he was first "Taught lots of discipline and dressage by a Hungarian Cavalry Officer". Note he says dicipline first. Then, he also loves the American Cowboy, so he mixes the two. He finds it necessary to tie the bit to the tail around the side of a horse to force it to bend and be obedient. Dicipline, no doubt. Or torture.
Martingales & Tie-Downs

There are several different more or less intricate tie-downs to use, that limit the height of the head. The simplest ones just go from the bridle to the chest, being strapped to the girth or to a harness around the shoulders. Some attach to the bit rings, some to the cavesson and some attach to the reins via running rings. The running martingale has been frequently used by jumper riders for quite some time, and are more or less standard issue nowadays. They are really quite useful in jumping situations, especially with horses that tend to evade the rein aids approaching a fence.
Hot or stubborn horses tend to throw their heads up, and I mean really throw their heads up. Not like going 'above the bit' in a dressage situation, but more at nose-the-highest-point running like mad. And the sporthorse breeds just keep getting hotter. The good thing about a running martingale, is that it is adjusted to come into effect only when it is needed. When the reins are pulled up above a certain level, the rings hold them back. This also makes the reins pull down, instead of back.

When the horse has thrown its head up really high, the reins only pull the bit towards the ears (head horizontal) and anything one can do with the reins in that angle will be useless. When the horse has its head in a more normal position, the straps are loose and do nothing. It also serves to keep the reins from going over the horse's head and hinders him some from stepping on them, should the rider suddenly dismount.

The irish martingale has the same function of keeping the reins. And there is a simple piece of equipment, if ever there was one. You run the reins through the rings while the strap is under the neck of the horse. This makes the strap go against the underside of the neck if the horse raises the head, and this is where the rings will offer resistance. When the horse behaves well they come out of action. Just one problem...

Most martingales are not long enough, or split enough to allow for an opening rein aid. That might be fine in show jumping, but in dressage it is disasterous. The irish martingale allows almost nothing of movement sideways, and can sometimes hold the reins together closer than the rider would in a neutral position. So they are for jumping and not for basic training on flat ground.
There are numerous tie-downs, or standing martingales around. These are static length straps that go from the head to the chest. The harbridge rein is one such tie-down. It either attaches to the noseband, like any standing martingale. It sounds quite innocent, and truthfully, it's not that bad. A real downer about it is that it doesn't have any elastic, so when it comes into action, it can to so with quite a snatch.

On a very few horses, with vices such as rearing, this can be life-threatening. There's enough room for the horse to gain momentum with the neck, and when it is pulled taut, the horse can freak out, and rear and flip over. Scary.
With a simple extra converter it can be attached to the bit rings, too. That is naturally much harsher, and naturally, the same thing can happen as with the regular attachment as described above. But with this attachment something much more severe happens - the bit rings are pulled down and together, creating a nut-cracker effect with the point of the joint of the bit going straight up into the pallet. That, if anything, can cause the horse to rear or run away with its rider.
Alliance Back Lift
I have now found my way into the English part of the website and read about this thing, finally. I'm a little less confused now.
I have of course still not tested this "auxiliary rein", but some things I can still say about it.
1 It appears to work on the right influence on the front end - it attempts to lift the base of the neck.
2 It is not attached to the mouth, and does not appear to make the horse curl in behind the vertical.
3 It is still a static contraption that CAN be used to force the head down, instead of "asking" for a stretch. Read further here...
Throughout this reading, you must have by now realised that all these contraptions are concentrated around one specific part of the equine anatomy - the head.
Instead of Gadgets
I'm on a mission.
I'm searching for the lost "positioning" at the poll. Everywhere I go, everything I read, it's about bend, flexion, contact, activity, drive-drive-drive etc. But nowhere does the old concept of positioning near the poll emerge. I think it has been totally forgotten.
At the same time, I constantly observe what Paula Kierkegaard (US judge and trainer) refers to as precipitous flexion, premature flexion or direct flexion, for those of us less steeped in the English language. Direct vertical flexion of the head to make the horse come to the bit. When I was at riding school as a kid, we were NOT ALLOWED to pull alternately at the reins to get an outline. We were not allowed to shorten the reins strongly and kick on until we got an outline, either. We weren't taught about outline at all. No riding teacher ever mentioned "on the bit". We were taught to ride careful corners, with positioning at the poll just before the corner, careful bend through the corner and a tad of a release after the corner. In every corner. The same for circles, voltes, turns on haunches and forehands. Even the dreaded leg-yield.

I can't remember ever talking about "on the bit" as a child or teenager. But I was a child, and don't remember all of it, anyway. But I do know, that from riding these exercises with careful positioning, the horse got really soft, and comfortable to sit on. I rode Jino, dreaded for his schwedengang and hard-to-sit trot. He was really nice. There was an x-competition horse that the school had bought. I never managed to ride him well, to sit his trot, because the corners and figures never worked to get him soft and comfortable. He was resistant, and stiff in the back. My guess is, he had been the victim of premature, direct vertical flexion in his previous career as a competition horse.
Horses that are "forced" to flex by pulling the nose in or pulling the head down, flex behind the 2nd vertebra. They stiffen between the 2nd vertebra and the poll in self-defence. Good positioning, with the bend between the 1st and 2nd vertebra and a release of the outside rein, will decontract this stiffening of the poll and stretch the neck out. If you manage to move the inside hingleg to step further in under the body and towards the midline (aim for the outside fore) the release will come from the pelvis and hip, over the back and to the mouth, and be a mature flexion (as opposed to an immature one).
I was on a mission in Finland in the early spring of 2005. I had not been there before and did not know the riders or the horses. They didn't know me either. Theory-wise we went through the bio-mechanics of the "shoulder-in volte" how to get a stretch and how to alternate between working and stretching. They all agreed and understood the theory.
Then we got into the riding arena. It was harder than it sounded to convert the theory into the real thing, and mainly because of one thing. The riders were terrified of opening the inside rein. They had been yelled at for doing so, probably, or repeatedly informed that it is Verboten! And now I asked that they commit the forbidden act...
The next hardship was to actually release the reins forward when the horse began to stretch. Many riders had the well cultivated reflex of snatching the reins back as soon as they were released a little. Probably because they had previously been instructed to Shorten the reins!
Practice makes perfect, and although most of the riders didn't arrive at perfect just yet ;-) they got to feel just how the back feels as the horse releases it into a stretch. The ball was set a'rollin'. It was hard for all of them, however, because riding is soo much about aquiring the right set of habits and cultivating them to work without having to think of every little thing every time. Then to change that... Well, they did good.
Almost all horses respond to positioning in the poll and crossing over with the hindlegs. I have dealt with extremely thick-throated ponies, where it was really hard-won to get first a lateral flexion in the right place, and then a stretching release. But that's both conformation, as well as being ridden by an uneducated kid with a sharp pelham for 10 years. And still they would generously release when the rider got the coordination and timing right
Theresa Sandin. Sustainable dressage