One of the things that I always strive for is to engage and to activate the hind legs as much as possible. In traditional riding lessons, the way to obtain more activity always seems to be “more leg”. But that’s not really correct. If you drive more, if you use stronger leg aids, you stiffen your leg muscles, which blocks your hip joints, which blocks the horse’s back and hind legs. Gripping or kicking legs cause the horse to hold his breath and to brace his rib cage, which also kills the impulsion and the back activity. I have ridden horses that would actually stop and kick at your leg or try to bite your toes (usually stallions), if you were gripping at all.
The secret to better engagement and activity is really not to do anything with your seat that can block or slow down the hind leg movement. “Take the foot off the brake, before you step on the gas” is something I used to tell students who took longe lessons on our horses in the US and weren’t able to keep the horses in the trot. Most of them would immediately kick the horse to keep him going, although they themselves were the reason why the horse fell back into the walk. The less you interfere with the horse’s back movement, the less you need to drive.
If the seat is static and very heavy, with most of the weight resting on the seat bones, it deadens the movement of the back. Stiff hip and knee joints will do the same, by the way. A static, heavy seat prevents the back from lifting, which forces the hind leg to step short. If the hind leg touches down too soon, it will be too far behind the center of gravity, which shortens the flexion phase vis-à-vis the pushing phase. The result is a stiff horse that is on the forehand and uncomfortable to sit.
Enhancing the upswing of the horse’s back can be accomplished by extending your hip and knee joints slightly as the horse lifts up into the suspension phase of the trot so as to create a little space underneath your seat bones which the horse can fill with his back. When the horse lands again after the suspension phase the rider’s hip and knee joints flex again and she can let her weight rest more on her seat bones again. If we want to lighten the seat by swinging a little higher with our pelvis, we need to support ourselves not with our seat bones at that moment, but somewhere lower down. The insides of our knees and thighs can temporarily receive some of the weight (but without gripping!) that was resting on our seat bones before. This gives the seat greater stability and greater mobility at the same time. When you can find additional support somewhere below the horse’s spine and below your seat bones you actually end up sitting deeper in the horse, whereas if all your weight rests on your seat bones you end up feeling stuck on top of the horse’s back.
Of course, if you focus exclusively on swinging up and lightening your seat, the horse will pretty soon start to fill the space underneath your seat by pushing his croup up and falling onto the forehand. So we need to emphasize the downswing after the suspension phase occasionally as well, when a hind leg lands and flexes its joints.
Emphasizing the upswing, the downswing, or the lateral swing of the back is not something you need to do every stride. Otherwise, it would get too hectic. You can “cruise in neutral” for a few strides, then emphasize the upswing, if you feel like the horse needs to lift his back and engage his hind legs more. You can emphasize the downswing for a couple of strides if you feel like the hind legs need to soften and flex a little more. Then you return to neutral for a few strides, etc. All actions are taken on an “as-needed” basis. They are not mechanically repeated every stride. The seat has to be a living, breathing, dynamic entity, not dead weight or a hard brick that presses the horse’s back and hind legs into the ground all the time. One more thing that needs to be pointed out is that these movements of the seat are so small that an observer won’t be able to see them, but big enough for the horse to feel them. So, allowing the horse’s back to lift and his hind legs to engage through the dynamic use of the seat is one aspect. The other part of the equation is that the horse needs to support himself well with one hind leg while the opposite one is in the air. The more the grounded hind leg flexes first, the more forward-upward it can propel the other hind leg when it is pushing against the ground during the extension phase of its joints. Horses that are not well connected to the ground and the weight typically don’t use the full range of motion of their hind leg joints, and they usually don’t move through their back. They feel more or less stiff and uncomfortable.
Connecting the horse’s legs to the ground and allowing the back and withers to lift results in a horse that is very active, very round, and moving properly through his back.
This dynamic, flexible use of the seat can be augmented by other aids. For instance, you could apply a driving leg aid as your seat is swinging up, which will then increase the engagement of the hind leg on this side as well as the lifting of the back. If you consistently lighten your seat slightly when you drive with your leg, the horse will connect the dots and may end up becoming more active when you lighten the seat without a driving leg aid because he associates the upswing of your seat with the driving leg aid. While you’re emphasizing the downswing of the horse’s body you can apply a half halt and/or a stirrup pressure. That is the moment one of the hind legs is touching down and starting to flex its joints. Accentuating the flexion phase of the grounded hind leg can lead to deeper flexion, shorter and higher strides, or a slower tempo, depending on what you want to achieve.
