In modern dressage, the double bridle is often used as if both bits were designed identically. Most riders hold all four reins with the same tension. So the horse and rider don't get the benefit of the finesse of two bits that are designed differently and act very differently. The double bridle is not intended as a part of a costume. It is not there to get the head down. It is not there as brakes to stop your horse! In reality, the double bridle can bring a whole new dimension to the conversation with your horse.
For me, introducing the double bridle is almost like being slightly near-sighted and putting on glasses. With glasses, I can see a lot better. With a double bridle, you can feel a lot more details because you receive information through four reins and two different channels. And you can talk to the horse even more precisely than with just a snaffle.
By using the two bits differently according to their design, you double the vocabulary with which you can talk to the horse. The conversation can become more sophisticated, you can frame the shoulders better, you can connect the base of the neck more securely to the shoulders, and you can align the horse more precisely.
From a gymnastic point of view, you can flex the hind legs more effectively by using a double bridle. One of our old teachers used to say that the curb bit acts more on the skeleton and the snaffle more on the musculature. You can really feel the joints of the hind legs fold more when you half halt with the curb bit. You feel the half-halt go through in a more profound way than with a snaffle.
Because of the different design, the snaffle bit is better suited for bending and for elevating. The curb bit is more suited for longitudinal flexion of the poll, but also of the hind legs. Since the half halts you apply by closing your fingers on the curb reins flex the hind legs more effectively, you indirectly get more relative elevation of the forehand as a result of the increased flexion of the haunches.
Historically, in a military context, the trained horse needed to be ridden with a double bridle because it made stopping and turning easier, especially in highly stressful combat situations. In that context, the use of the double bridle was more about control than sophistication. It was always introduced at the end of the elementary training when the horse was able to walk, trot, and canter, and to perform all the transitions between the gaits, including the more difficult ones, like trot - halt, and canter - halt.
In the French tradition, the double bridle tends to be introduced earlier than in the German tradition. Some followers of François Baucher, such as James Fillis, actually even started green horses in a double bridle. Fillis never rode his horses just with a snaffle.
In modern dressage competitions, the use of the double bridle starts in Germany at Klasse L, which is the equivalent of USDF Second level. In the US it starts at Third level. Essentially, when the lateral movements in the trot and the flying changes in the canter start to show up in the competition tests, that's where the double bridle is either permitted or even mandatory. In German competition tests, there were no lateral movements in Klasse L. This was the end of the traditional basic training of the cavalry horse.
In Germany, the military tradition is still followed in that the double bridle is introduced before the lateral movements (excluding leg yields). I personally prefer to begin with lateral movements earlier in the training but to wait longer before introducing the double bridle. Gymnastically, it makes more sense to incorporate the lateral movements and their precursors earlier than in the military tradition. The double bridle is not really beneficial until the horse is able to step far enough underneath the body weight, which is what sidestepping exercises with the bend against the direction of movement are designed to do (among other things).
It is important not to become too reliant on the double bridle. Even once the horse has graduated to wearing a double bridle, it has to be possible to ride everything in a plain snaffle too. Some riders never return to the snaffle once they have introduced the horse to the double bridle. Their horses then become stiffer and stiffer, until they can’t be ridden on the bit in just a snaffle, or they become difficult to stop or to bend. This creates a whole series of new problems.
If someone rides their horse only in the double bridle because work in the snaffle is too challenging, it is like sweeping dirt under the rug. They are not really addressing the issues that are still there, but they are merely covering them up with the double bridle. It is important to ride the horse regularly with a simple snaffle and to make him supple and pliable. And when you do that, it will make the work in the double bridle that much better. Conversely, when you return to the snaffle after a couple of days in the double bridle, the horse should go better in the snaffle than he did before the double bridle days.
In Germany, it was customary when I was a teenager that upper-level horses were ridden in a double bridle once or twice a week, and then the rest of the week in a snaffle. In the Spanish Riding School under Podhajsky, they rode three days a week in the snaffle and three days in a double bridle. Always three days in a row. But for some of the horses we trained over the years, three days of the double bridle in a row was too much. I started seeing negative side effects of the double bridle, like getting short in the neck or dropping the withers. If your horse starts to curl up, get behind the seat and leg, falls more onto the forehand, steps short behind, etc. it’s a sign that you have been riding with a double bridle for too long and that it’s time to return to the snaffle for a while.
When we were actively showing and had to keep our horses tuned in the double bridle Shana used to do one day double, two days snaffle, one day double. Then during a show, of course, the horses would be in the double the whole time. After the show, they got a day or two off and were ridden in the snaffle afterwards.
As I said before, when you return to the snaffle bit after a day or two in a double bridle, the horse should go better in the snaffle than before the double bridle. However, if he is stiff and braced, then something went wrong. Maybe you were relying too much on the curb, or using the curb to cover up training deficits.
Used correctly, though, the double bridle can contribute a great deal to refining the training and the conversation with the horse, and to the development of greater precision in all movements.
