Introduction
We are probably all familiar with the phrase “Ride from the inside leg to the outside rein”. Teachers love to repeat it. Riders giving well meaning advice to fellow equestrians love to say: “inside leg to outside rein!” This sounds good. It sounds like they know what they are talking about. But what does it mean? Why should I ride from the inside leg to the inside rein? And how do I do that?
Big Picture
Goal
In order to make sense of the bumper sticker slogan “inside leg to outside rein” I have to make a big detour to start at the beginning and give you an overview over the biomechanics.
A good starting point is to ask ourselves: What is our dream goal in riding? Not in terms of fancy movements or going to the Olympics, but in terms of the quality of the gait? For the old masters the quality of the gait - or the purity of the gait, as they called it - was paramount. Nothing was more important than the quality of the gait because this directly impacts whether the horse stays sound or not and whether he is pleasant to ride or not.
My own personal vision of the perfect gait is that it is elastic, comfortable, round, energetic, and light. In gymnastic terms, this requires that the horse is straight, balanced, and supple. This, in turn, requires that both hind legs step far enough under the body and support the back from below by flexing their joints. If the hind legs are not flexing under the body, the back will drop, the horse will either invert or curl up, and all the roundness, lightness, suppleness, and fluffiness will go right out the window.
Obstacle
Unfortunately, the horse’s natural crookedness forms a big obstacle for engaging and flexing both hind legs underneath the body because the hind leg on the stiffer/convex side unfortunately to lag behind a little, while the hind leg on the hollow/concave side tends to move next to the body, rather than stepping underneath it. Consequently, we have to bring both hind legs underneath the body first before we can use the body mass to flex them in order to protect the back and create an effective shock absorbing system.
Engage the Inside Hind Leg
It’s easiest to engage a hind leg under the body mass when it’s the inside one (in terms of the bend) because of the lateral bend of the spine and the fact that the inside hip is placed slightly ahead of the outside one. We can use circles and voltes on a single track to create a lateral bend and to engage the inside hind, or we can use sidestepping exercises in which the horse is bent against the direction of travel, e.g. enlarging the circle (the so-called 1st Test of the Inside Hind Leg), shoulder-fore/shoulder-in (the so-called 2nd Test of the Inside Hind Leg on the circle), leg yield, turn on the forehand in motion. The rider’s aid that communicates with the inside hind leg in order to ask it to reach more under the body is the inside lower leg (the inside leg part of “inside leg to outside rein”).
Sidestepping is on the one hand more demanding than riding on a single track, but on the other hand it’s more effective, and it has the bonus effect of shifting the weight onto the hind leg that is not crossing, i.e. in shoulder-in related movements it’s the outside hind leg. Shifting the weight to the outside makes it easier for the inside hind leg to engage.
If you want to bring the outside hind leg more underneath the body, you can either change direction or you can use so-called counter movements like the counter shoulder-fore and counter shoulder-in (the so-called 3rd Test of the Outside Hind Leg on the circle), where the horse is bending towards the outside of the arena. If you want to changing direction in order to address the opposite hind leg, you can ride figure 8s and serpentines.
The Outside Rein
When you engage the inside hind leg in the direction of the outside front leg so that it steps closer to the inside hind leg and closer to the center of gravity, the muscles on the outside of the bend will expand and the horse will stretch into the outside leg and rein of the rider. Once the rider can feel the horse in her outside hand, the outside rein is able to start communicating with the horse, but not before. As long as the outside rein is empty, there is nothing you can do with it.
As soon as the horse initiates contact with the outside rein, you can begin to recycle the energy impulse that originated with the inside hind leg swinging forward by creating a connection through the outside hind leg into the ground, which completes the circle of aids.
The most common aid that is used to flex the outside hind leg between the ground and the weight is the half halt on the outside rein when the outside hind leg touches down (the so-called 1st Test of the Outside Hind Leg).
The Outside Hind Leg
The outside hind leg has the function of an anchor or stabiliser in turns as well as in lateral movements in which the horse is bent against the direction of travel. The old masters said that the quality of a turn is only as good as the rider’s connection to the outside hind leg. This applies to 20m circles, as well as to corners, voltes, and even pirouettes.
When the outside hind leg disconnects, the horse will usually fall onto the inside shoulder and counter bend.
As soon as the outside hind leg is connected to the ground and the rider can determine precisely how much it flexes and how much weight it supports, the inside hind leg is free to swing forward, the rib cage is able to swing to the outside, and the spine is able to bend along its entire length.
The engagement of the inside hind leg and the flexion of the outside hind leg form a feedback loop. The more the inside hind leg engages, the more the rider can flex the outside hind leg. And the more the outside hind leg flexes, the easier it is for the inside hind leg to swing forward.
Practical Considerations
From the previous paragraphs, you can see how important it is that both hind legs step underneath the body and support the back by flexing their upper joints. However, as I mentioned before, the hind leg on the stiffer side tends to take shorter steps and lag behind because the hind leg of the hollow side doesn’t stay on the ground long enough, and it tends to move alongside the body instead of stepping underneath it.
This means that we need to take action to engage and flex both hind legs. Since it is easier to engage and flex one hind leg at a time than both simultaneously, we will alternate between engaging and flexing the left hind leg and the right hind leg. Due to the mechanics of the lateral bend, it is easier to engage the inside hind leg than the outside one.
First Degree Bending
When we ride in the horse’s stiff/convex direction, he will initially step short with the inside hind leg and lean on the inside shoulder and rein. The croup will swing to the outside and the outside rein has no contact. The simplest remedy is to ride a circle and enlarge from the inside leg (1st Test of the Inside Hind Leg). If the horse is leaning onto the inside rein and not approaching the outside rein, the inside leg and rein have to support the rider’s seat and weight aids as well as each other in taking the horse out. The inside leg addresses the inside hind leg, and the inside rein addresses the inside shoulder. When the inside rein applies a half halt towards the outside hind leg so that the excess weight is transferred from the inside front leg to the outside hind leg, this is called the 2nd Test of the Outside Hind Leg.
As the horse is starting to shift the weight onto the outside pair of legs the spine will begin to the inside. This used to be called “1st Degree Bending”, i.e. the inside leg and rein bring the horse to the outside leg and rein, which results in a lateral bend to the inside. For young horses and rehab horses this is often the starting point for bending work in motion.
Second Degree Bending
Once the horse has discovered the outside rein and makes contact with it, we can recycle the energy to the hindquarters and apply half halts with it into the outside hind leg (1st Test of the Outside Hind Leg). The outside rein then also has the function of framing the base of the neck and connecting the base of the neck to the shoulder so that the neck can’t become unstable and overbend. At that point the inside rein can actually apply some laterally flexing aids to supple the poll region, while the outside rein is providing stability and a connection all the way back to the outside hind leg. When the horse is able to accept diagonal aids, the old masters used to call this type of bend “2nd Degree Bending”.
Pingpong
If we want to address the other hind leg, the one that is facing the outside of the arena, we either change direction or we stay on the same rein and use a counter movement (i.e. a movement in which the horse is bent towards the outside of the arena). Frequent changes of rein and changes of bend prevent one hind leg from escaping by being “unsupervised” for too long. This is one of the reasons why figure 8s and serpentines are so effective.
When we alternate between engaging the left hind and the right hind leg every few strides we can send the horse from the old inside leg to the new inside leg so that he starts rolling back and forth like a ball. Every change of bend requires a weight shift onto the old inside hind leg. The reason for this is that you hold the old inside hind leg on the ground a little longer so that the new inside hind leg is free to pass the old one and reach farther under the body.
This combination of shifting the weight and changing the bend is an integral part of every change of direction, every simple lead change in the canter, every flying lead change, and every transition between shoulder-in and renvers, or counter shoulder-in and haunches-in.
Practicing these weight shifts and changes of bend has an excellent straightening and suppling effect on the entire horse. Many horses find them difficult at first, but the better they get at them, the rounder they feel and the easier it is to roll them like a ball in any direction at any time.
Summary
Inside leg to outside rein is an abbreviation for a relatively complex set of movement patterns that result in a very supple, balanced, straight, and agile horse.
The job of the inside leg is to initiate the circle of aids by bringing the inside hind leg closer to the outside one as well as closer to the front legs.
This results in a weight shift from the inside shoulder onto the outside pair of legs, which results in an expansion and stretch of the muscles on the outside of the horse’s bend.
Bending and stretching the muscles to the outside creates a contact with the outside rein, which is then able to connect back to the outside hind leg. The outside rein can half halt into the outside hind leg, i.e. press it briefly into the ground to flex its joints with the help of the combined weight of horse and rider.
Since the hind legs are similar to coiled springs, flexing/compressing them between the ground and the weight creates an equal and opposite impulse to extend and push again. The extension of the joints of the outside hind leg and the pushing power it generates can be harnessed by the rider an directed either in a more vertical direction (more collected gaits) or in a more horizontal direction (medium and extended gaits). The skilful alternation between engaging, flexing, and releasing the hind leg builds power and impulsion.
I hope this helps to unravel the mystery of the “inside leg to outside rein” mantra and shows you the possibilities that are behind the brief slogan. And I hope some of the biomechanical explanations give you some ideas of how to create the inside leg to outside rein connection, how to “get the horse into the outside rein”, how to improve the bend, and how to establish a “circle of aids” because they are all connected to each other.
