Auxiliary reins — often loosely called side reins as a catch-all term — are straps or cords that limit a horse's posture, usually during lunging and sometimes under saddle. Few pieces of equipment divide opinion in the horse world as much: some see a useful tool for focused work, others see a shortcut that hides problems. This guide lists the best-known types, describes what they do and don't do, and sets out the limits within which their use is defensible.
What an Auxiliary Rein Does — and Doesn't Do
The starting point: an auxiliary rein limits a posture, it doesn't teach a horse anything. The strap can stop the nose from going too high or the neck from bending too far sideways, but it doesn't explain why a lower, rounder posture is actually more comfortable. That understanding only comes from correct training: a horse learning to move from back to front and to use its back, as described in suppleness: getting your horse to work over the back.
The debate around this is real, and both camps have a point. Supporters point out that a correctly adjusted auxiliary rein on the lunge provides a frame: the horse gets a clear boundary, can find its balance within it, and gets used to steady contact without a rider's hand. Critics counter that a horse within a fixed boundary mostly learns to evade the pressure — and that the shape you see then says nothing about the muscles and balance underneath. Both observations are correct; the difference lies in the adjustment, the duration, and the purpose for which the rein is used.
The Best-Known Types
| Auxiliary Rein | How It Works | Typical Context |
|---|---|---|
| Side reins (uitbinders) | Fixed straps from girth to bit; limit the neck sideways and upward | Lunging |
| Lauffer reins (triangle reins) | Run from the girth, between the front legs, through the bit rings, and back; leave room forward-downward, limit upward | Lunging |
| Chambon | Works via the poll; applies pressure as soon as the head comes up, encouraging a lower posture | Lunging |
| Gogue | Related to the chambon, but continues through to the bit; keeps the invitation to go lower in place during movement too | Lunging |
| Draw reins | Run from the girth through the bit rings to the hand; the rider sets the limit moment to moment | Under saddle, experienced hands |
A few notes on the table. Side reins are the simplest and most widely used variant, but also the most rigid: the length is fixed, regardless of what the horse does. On the lunge, Lauffer reins are often the friendlier choice, because the horse can stretch its nose forward and down — exactly the direction you want to see during loosening work. The chambon and gogue actively encourage a lower posture through poll pressure and therefore demand more knowledge from the user. Draw reins under saddle are a case apart: in experienced hands a finely adjustable tool, but the potential for misuse is high, since a rider can roll a horse in behind the vertical without it being obvious.
When an Auxiliary Rein Can Make Sense
There are situations where an auxiliary rein is defensible, and they share common features: short in duration, with a focused goal, and almost always on the lunge. Think of a horse that consistently runs around with its nose in the air while lunging and, as a result, never settles into a relaxed trot, or of evening out the contact with a young horse that already knows how to lunge — the first lessons themselves should be given without auxiliary reins, as described in what is lunging: the first lessons.
The adjustment determines whether the tool helps or harms. Correctly adjusted means: the horse can keep its nose in front of the vertical and has room to stretch forward and down. An auxiliary rein that locks the head into a shape is by definition too short — at that point you're no longer limiting, you're forcing.
Where It Goes Wrong
Most damage comes from adjusting too short. The horse does take on the desired shape, but without using its back: the neck curls, the back stays hollow, and the hind legs slide out behind the body instead of stepping under it. From the outside it looks round; in reality the horse is learning to creep behind the contact — retreating from the pressure instead of working into it.
A second pitfall is masking. A tense underneck or a hollow back doesn't disappear just because you put a strap around it — it only becomes invisible. Anyone who removes the auxiliary rein and sees the same tense picture return has trained for weeks without building anything. And because the shape looked acceptable with the auxiliary rein on, the problem often goes unnoticed until late.
The Alternative Is Usually Better
For almost every purpose an auxiliary rein gets reached for, there's a slower but more durable route: correct lunging on a large circle, plenty of transitions, and letting the posture emerge from relaxation instead of imposing it. Suppleness is built from back to front — an active hind leg, a swinging back, and only as a result of that a neck that rounds. A strap can't force that sequence; time and systematic work can.
The rider's hand is part of this too. Anyone who reaches for draw reins under saddle because the horse won't come onto the contact is usually solving the wrong problem — the cause more often lies in riding technique or a lack of basic training than in the horse. A properly fitted bit, used correctly, does more good than an extra strap.
The rule of thumb: an auxiliary rein doesn't compensate for a lack of basic training. And if you're unsure about its purpose or adjustment, have an instructor take a look — the adjustment itself is exactly the moment where experience makes the difference.
Competition Context
Auxiliary reins aren't allowed in the dressage arena; you ride your test on a snaffle or a double bridle without any extra restriction. For warm-up and lunging areas at competitions, rules vary by federation and by discipline — check before you leave what's allowed at your competition via knhs.nl (the Dutch equestrian federation).
In Short
- An auxiliary rein limits a posture but teaches a horse nothing — the training itself has to build the understanding.
- The debate is real: a frame on the lunge can be useful, but a fixed boundary also invites evasion.
- Lauffer reins and (in skilled hands) the chambon leave room forward-downward; draw reins under saddle carry the greatest potential for misuse.
- Correctly adjusted means nose in front of the vertical with room to stretch; locking it down forces a shape without the back and teaches the horse to creep behind the contact.
- The alternative is usually better: correct lunging, transitions, and building suppleness from back to front.
- Auxiliary reins aren't allowed in the dressage arena; warm-up and lunging areas at competitions are governed by federation rules (knhs.nl).
See also: What is lunging: the first lessons · Choosing the Right Horse Bit · Suppleness: getting your horse to work over the back · Glossary: lunging · Level: Considering Your Own Horse