Why Do We Ride on the Correct Diagonal in Rising Trot?

I was tagged in a video on social media recently where someone asked a really good question:

"Why do we ride on the correct diagonal in rising trot?"

One explanation you'll often see in magazines, coaching manuals and online articles is this:

"The correct diagonal in rising trot refers to rising when the outside foreleg and inside hind leg move forwards and sitting when they move back. This timing allows the horse's inside hind leg, which generates most of the propulsion around turns, to move freely and take a longer stride."

It's a neat explanation and it's easy to understand why it's been repeated for years, but the problem is that it blends together traditional coaching theory, biomechanical assumptions and research findings as though they're all established facts. When you actually go back and read the papers themselves, the picture is both more interesting and more nuanced.

The research certainly demonstrates that changing diagonals alters the interaction between horse and rider, but it doesn't conclude that the inside hind simply moves more freely or takes a longer stride. That doesn't necessarily mean the traditional explanation is wrong. It simply suggests that the real reason is probably more complex.

To understand why, I think we first need to step back and ask a different question.

Why do we rise to the trot in the first place?

Trot is often described as a spring-like gait. As each diagonal pair of limbs contacts the ground, the horse's muscles, tendons and ligaments store elastic energy before releasing it to propel the horse forwards and upwards into the next stride. That upward movement doesn't stop at the horse's back. It continues through the horse's trunk into the rider.

As riders, we can respond to that movement in two ways. We can remain seated and absorb the horse's movement through our pelvis, spine and lower limbs, or we can use some of the energy the horse has already generated to initiate the rise.

The important point is that we aren't pushing ourselves out of the saddle every stride. If we were, rising trot would be exhausting. Instead, the horse accelerates our body upwards and we simply organise ourselves so that movement can happen efficiently. A stable lower leg provides the base of support, the knee acts as a pivot allowing the thigh to arc forwards as the hip extends, and the pelvis remains organised rather than tipping forwards or arching through the lower back.

The highest point of the rise is often described as the point where the rider is "lightest", but that isn't really what's happening. The rider hasn't become weightless and the horse isn't supporting less body weight. Instead, it's the point where the rider reaches the top of the rise before their downward movement towards the saddle begins.

At this point, a greater proportion of the rider's body weight is supported through the stirrups, which temporarily become the rider's primary base of support. The horse is still supporting exactly the same rider, but the pathway through which the load enters the horse has changed. Rather than passing predominantly through the rider's seat into the horse's back, a greater proportion is transmitted through the feet, stirrups, leathers and saddle tree into the horse's thorax.

Gravity then accelerates the rider back towards the saddle. As the rider returns, the horse doesn't simply support the rider's body weight. It must first absorb the rider's downward momentum before generating the upward force needed to propel both horse and rider into the next stride.

This distinction is important because the rider isn't just adding weight to the horse. They're adding timed loading. The supporting limbs must absorb the rider's downward momentum before generating the force needed to accelerate both horse and rider into the next stride.

Whether those forces are beneficial therefore depends on when they occur.

Straight line versus circle

On a straight line, a sound horse aims to move relatively symmetrically. The left and right diagonal pairs alternate their roles from one stride to the next, so neither side is consistently being asked to perform a different job from the other.

On a circle, that symmetry naturally changes.

Straight Line vs Circle.  Different Forces. Different Movement.

The horse isn't simply travelling forwards. It must also continually redirect its centre of mass towards the middle of the circle whilst maintaining forward propulsion. From a biomechanical perspective, this means the inside and outside limbs can no longer perform identical mechanical roles.

The paths they travel are different as well. The inside hind follows a smaller radius, whereas the outside hind follows a larger one. The outside hind therefore travels a longer path during each stride, meaning the temporal and mechanical demands placed upon the two hindlimbs are no longer identical.

Once the limbs contact the ground, those differences continue. Studies have shown that the inside hind remains in contact with the ground for longer, whereas the outside hind experiences the greater peak vertical ground reaction force. At first glance, those findings appear contradictory. If the outside hind produces the larger force, doesn't that mean it's doing more work?

Not necessarily.

Peak force simply tells us the greatest force produced at one instant. It doesn't tell us how long that force is applied. The inside hind, despite producing a lower peak force, remains on the ground for longer. This means it generates force over a greater period of time, resulting in a similar, and in some studies greater, total vertical impulse. Impulse is simply the total amount of force applied over time. A large force applied briefly can produce the same overall impulse as a smaller force applied over a longer period. In other words, the inside hind isn't necessarily working less than the outside hind. It's simply contributing differently.

The outside hind produces a larger peak force over a shorter period, whilst the inside hind supports the horse for longer. Together they allow the horse to support its body weight, continue moving forwards and continually redirect its centre of mass around the bend.

This is consistent with movement symmetry studies by Greve and Dyson, which showed that predictable asymmetries in head, wither and pelvic movement occur even in sound horses simply because they are travelling on a curve. Predictable asymmetries in head, wither and pelvic movement occur even in sound horses simply because they are travelling on a curve. Maintaining ground contact for longer allows the inside hind to continue producing force over a greater proportion of the stride, whereas the outside hind produces a larger force over a shorter period.

The horse is therefore already moving asymmetrically before the rider even returns to the saddle.

From a biomechanical perspective, that becomes important because every time the rider returns towards the saddle, one diagonal pair is responsible for supporting not only the horse but also the rider's downward momentum. Changing diagonals doesn't change how much the rider weighs. It changes when that weight and momentum are applied to a horse that is already moving asymmetrically.

If that reasoning is correct, we would expect changing diagonals to alter the loading experienced by the horse.

The obvious question is whether the research actually shows that.

What makes a correct diagonal in rising trot on a circle

The first question researchers needed to answer was whether changing the rider's diagonal actually altered the forces acting on the horse. If changing diagonals didn't affect loading, then none of the traditional explanations could really be true. If it did, the next question becomes whether one loading pattern is more beneficial than another.

This is exactly what Roepstorff and colleagues investigated. Their study demonstrated that changing the rider's diagonal altered the horse's vertical ground reaction forces, together with changes in pelvic, spinal and limb movement. During the rider's seated phase, the diagonal pair supporting the horse experienced greater loading. Changing diagonals therefore changed which diagonal pair experienced that additional force.

The differences were relatively small, but they were consistent enough to demonstrate that changing the timing of the rider's movement changes how forces are distributed throughout the horse-rider system. Importantly, however, this wasn't the conclusion many people have since attributed to the study. The researchers did not conclude that the inside hind moved more freely, that it took a longer stride or that it generated more propulsion. What they demonstrated was that changing diagonals changes the timing and distribution of forces acting throughout the horse's locomotor system.

Demonstrating that changing diagonals alters loading is one thing. The more important question is whether one of those loading patterns is actually preferable.

This is where the work of Persson-Sjödin and colleagues becomes particularly interesting.

Rather than simply measuring ground reaction forces, they investigated whether riding on different diagonals influenced the horse's movement symmetry whilst travelling on a circle.

Their findings suggested that riding on the traditionally correct diagonal rendered the horse's movement more symmetrical than riding on the opposite diagonal, effectively counteracting some of the asymmetry created simply by travelling on a curved line.

However, it's important to read their conclusions carefully. When discussing why this occurred, the authors deliberately used the word "probably." They proposed a mechanism rather than proving one. Their explanation was that the timing of the rider's loading probably interacted with the horse's natural asymmetry during circular locomotion, reducing rather than reinforcing it. Again, they did not conclude that the inside hind was unloaded or that it simply moved more freely.

That is quite a different explanation from the one many of us learnt as children. Rather than the correct diagonal somehow allowing the inside hind to swing forwards more easily, the evidence suggests something more subtle. The horse is already moving asymmetrically because it is travelling on a circle. The rider then adds another loading pattern to that movement. Depending on when the rider returns to the saddle, that loading appears either to oppose or reinforce the asymmetry already present.

From a biomechanical perspective, this makes a great deal of sense. Changing diagonals doesn't alter the horse's mechanics in isolation. It changes how the rider's weight and downward momentum are superimposed onto a movement pattern that already differs between the inside and outside limbs.

That also helps explain why we change diagonals when riding on straight lines. On a straight line there is no inside or outside limb performing a consistently different role. Repeatedly riding on the same diagonal would therefore introduce the same loading pattern into what is otherwise intended to be a relatively symmetrical gait. By regularly changing diagonals, we avoid repeatedly loading one diagonal pair in the same way over prolonged periods of work.

On a circle, however, the horse is already asymmetrical. The evidence currently suggests that the traditional "correct" diagonal reduces some of that natural asymmetry, whereas the opposite diagonal appears to reinforce it.

The traditional coaching advice therefore still appears to be the right one. It's simply the explanation behind it that has evolved.

Could the "wrong" diagonal ever be useful?

Perhaps the most interesting implication is that this changes how we think about the so-called "wrong" diagonal. If the correct diagonal appears to reduce circle-induced asymmetry, it is reasonable to hypothesise that deliberately riding on the opposite diagonal could, in some situations, increase the mechanical demands placed on a particular limb or movement pattern.

In rehabilitation, we manipulate load all the time. We progressively load tendons, alter movement patterns and increase the demands placed on tissues to stimulate adaptation. From that perspective, deliberately choosing one diagonal over another could potentially become another variable that influences how forces are distributed through the horse-rider system.

However, this is where it's essential to distinguish between evidence and hypothesis. The current research demonstrates that changing diagonals alters loading and movement symmetry. It does not demonstrate that riding on the opposite diagonal strengthens a particular limb or should be used as a rehabilitation technique. At present, no published studies have investigated that question directly.

It is therefore a biomechanically plausible idea, but not an evidence-based recommendation. Perhaps that's what I find most fascinating about biomechanics. It rarely tells us that traditional coaching was wrong. More often, it explains why those traditional principles work. Sometimes it also shows that the explanations we've repeated for years have become oversimplified as our understanding has improved.

Riding on the correct diagonal probably isn't about magically freeing the inside hind.

It's about recognising that every time we rise and sit, we change when our weight and momentum are transmitted through the horse-rider system. On a straight line, regularly changing diagonals helps avoid repeatedly introducing the same loading pattern into a symmetrical gait. On a circle, the evidence suggests that the traditional diagonal times that loading in a way that reduces, rather than reinforces, the horse's natural asymmetry.

The traditional rule may still be exactly the right one. We simply have a much better understanding of why.#

If you've enjoyed this way of thinking about riding, this is exactly the approach I take at Pegasus Physio. Whether I'm working with riders in the Rider Physio sessions or through the online Riding Ready courses, my aim isn't simply to tell you what to do. It's to help you understand why by applying the science, anatomy and physics behind rider position and movement. Once you understand the principles, you can adapt them to your own horse, your own body and your own riding, rather than relying on rules alone.