On the surface, this sounds like a straightforward exercise. However, as with everything in dressage, nothing is ever as simple as it first seems.
Changing the rein across the long diagonal can present quite a few challenges for the dressage rider.
In this article, we take a look at what can go wrong, some of the common rider mistakes, and how you can ride this exercise for maximum marks in a dressage test.
What are the long diagonals?
In a dressage arena, the long diagonals run from the corner markers F to H (or H to F), and K to M (or M to K).

For reference, examples of short diagonals are F to E, and K to B (see below). You are still riding a diagonal line but, as the name suggests, it’s shorter.

In this article, we’re mainly focusing on the long diagonals however the same principles apply when riding the short diagonals.
What the judge is looking for
When judging a change of rein across the diagonal, here are a few things that the judge expects to see:
- The rhythm and tempo of the pace are maintained.
- The horse remains in balance.
- The horse is straight on the diagonal line.
- The horse shows clear, correct, and uniform bend through both of the corners.
- The movement is ridden accurately from marker to marker.
On top of that, the horse should continue to work forward through his back to seek an elastic contact with a consistent, correct frame. The horse’s balance should be uphill and off the forehand with light, mobile shoulders and active hindquarters relative to the horse’s level of training (i.e. the more advanced the level, the more of an uphill balance is required).
How to change the rein across the long diagonal
For this example, we are going to change the rein F to H across the long diagonal, going from the left rein to the right rein.
Step 1 – Ride a good corner
How you ride the corner preceding the diagonal line will determine the quality and accuracy of the movement. If you ride a bad corner, you’ll probably ride a bad diagonal line.
Use the corner to further engage your horse’s hind legs. This will help prevent a loss of balance when on the straight line.
To do this, whilst on the left rein and before entering the A/F corner, prepare your horse by riding a half-halt and look ahead of you to plan the turn. Establish the correct uniform bend through your horse’s body and keep him balanced between your inside leg and outside rein whilst continuing to ride forwards. Riding forwards will encourage the horse to step under with his inside hind leg.
You should ride as deeply into the corner as is appropriate for your horse’s stage of training.
Step 2 – Position your horse on the diagonal line
As you are riding through the corner, look up towards the arena letter that you are aiming for on the opposite side of the arena, in this example, that’s H. This will help you to position your horse accurately.
As your horse’s shoulders reach the F corner letter, you should be leaving the outside track through a smooth curve. Avoid making a sharp-angled turn as this could cause your horse to lose balance and straightness.
Ensure you have a secure outside rein contact to prevent too much neck bend and the horse clinging to the outside track.
Step 3 – Straighten the horse
Some riders assume that after turning their horses left, they then need to pull on the right rein to straighten the horse, or vice versa. That causes the horse to wiggle and lose balance and straightness.
To straighten the horse correctly and smoothly, simply put all your aids back to neutral whilst keeping a little bit more weight in your outside rein (your right rein in this example), and ride the horse forwards without rushing him.
To keep your line accurate, focus on placing the letter H between your horse’s ears and riding your horse through a tunnel using both legs equally.
Step 4 – Preparing for the next corner
A few strides before your reach the H corner marker, ride a half-halt to balance the horse and prepare him.
This is where you are going to change your diagonal (if in rising trot) and transfer your horse into your new outside rein (left rein) ready to re-join the track on the right rein.
Aim for your horse’s outside shoulder to reach the corner letter at the end of the diagonal line, rather than his head straight on. That ensures that the horse doesn’t hit the track at an angle that makes the turn too sharp.
Step 5 – Ride the corner
For the corner, ride your horse from your new inside leg into your new outside rein, whilst positioning your outside leg slightly behind the girth and using your inside rein to indicate the direction of bend and ask for a little inside flexion.
Look up and ride the horse forwards through the corner and away.
Why not change your diagonal over X?
When learning to ride and change the rein, most riders are taught to change their rising diagonal over X. Unfortunately, this can cause a few problems.
This is because X marks the center of the arena and it has no supporting walls or fence lines. By changing your diagonal here, whilst riding a straight line, you are highly likely to disrupt your horse’s balance.
It’s far more tactful to change your diagonal (and your outside rein) either before or after riding the straight diagonal line.
Here’s a quick rundown of how to do that.
Changing before the diagonal line
- Ride through the A/F corner on the left rein and with left bend.
- Position the horse onto the diagonal line and straighten the horse.
- Ride a half-halt, change your rising diagonal and your outside rein. (So, instead of having a bit more weight in your right rein, you now have a bit more weight in your left rein.)
- Ride the horse straight and forwards across the diagonal line.
- Prepare the horse for the corner and ride through the corner in right bend.
Changing after the diagonal line (also in the steps in our above detailed example)
- Ride through the A/F corner on the left rein and with left bend.
- Position the horse onto the diagonal line and straighten the horse, keeping a bit more weight in your outside rein.
- Ride the horse straight and forwards across the diagonal line.
- Just before reaching the H corner marker ride a half-halt, and change your rising diagonal and your outside rein. (So, instead of having a bit more weight in your right rein, you now have a bit more weight in your left rein.)
- Ride through the corner in right bend.
Doing it this way ensures that you are not going to disrupt your horse’s balance and rhythm at the crucial point of riding over X when the horse is already going to be at his least balanced moment. And since you are riding a straight line, you can be on either rising diagonal.
Common mistakes and troubleshooting
Here are a few common mistakes that happen when changing the rein across the long diagonal.
Problem 1 – The horse cuts the corner onto the diagonal line
If this happens, not only will your diagonal line be inaccurate but your horse will most likely be out of balance and on the forehand.
Cutting the corner is usually due to the horse leaning and falling inwards and/or the rider not establishing the correct uniform bend through the corner.
Remember to ride the horse from your inside leg into your outside rein to keep the horse out on the outside track.
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Problem 2 – The horse clings to the outside track
When trying to position the horse on the diagonal line it’s not uncommon to see horses cling to the outside track and overshoot the marker.
This usually happens because the rider has tried to turn the horse by using the inside rein in isolation. This creates too much neck bend and causes the horse to fall out through his outside shoulder. The result is that the horse turns his head to the inside, but his shoulders continue traveling straight down the outside track.
To correct this, use your outside rein to prevent too much neck bend and to control the horse’s outside shoulder.
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Problem 3 – Horse loses straightness
When traveling across the long diagonal, you want your horse’s hind feet to track behind your horse’s forefeet.
To help keep your horse straight, imagine that you are riding through a tunnel and keep your horse securely between your leg and rein aids and keep riding forwards.
Do not try to slow the pace in an attempt to try and straighten the horse because, more than likely, this will only result in the horse becoming more crooked.
Think of a bicycle. If you try to ride a bicycle in a straight line whilst pedaling slowly, you’re more likely to wobble. It’s much easier to cycle straight when you pedal faster. The same principle applies to the horse, so ride positively forwards.
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Problem 4 – Horse loses balance
When crossing over the center of the arena horses can sometimes lose their balance, fall onto their forehand, and/or come against the contact.
This can happen because the horse is on a straight line in the ‘middle of nowhere’ with no supporting wall or fence line to help balance.
You can help your horse keep his balance by preparing him diligently through the first corner. Use the required bend and a half-halt to encourage your horse to step further underneath with his hind legs. That will put him in the best position possible to remain in balance on the straight.
If you are still experiencing a loss of balance even after careful preparation, then change the rein via the short diagonals instead. Because they are shorter, there’s less opportunity for a loss of balance. You can progress to the long diagonals once the horse can keep his balance comfortably across a whole short diagonal.
Problem 5 – Horse loses rhythm and/or tempo
When changing the rein across the diagonal, regardless of if you are in walk, trot, or canter, the rhythm and tempo must remain consistent.
The horse should not speed up or slow down, nor should he break the pace (i.e. break into canter when he should be trotting).
These problems usually occur because of one of the following reasons:
- The rider tries to slow the pace in an attempt to keep the horse balanced and straight.
- The rider pushes the horse out of his natural rhythm and tempo in an effort to keep him straight.
- The horse loses its balance and rushes forward.
All of the above can be corrected by first ensuring that the horse is sufficiently prepared and balanced through the first corner, and second by riding the horse positively forwards without rushing him.
Count the rhythm and tempo in your head (for example for trot you would count 1, 2, 1, 2, 1, 2, or up, down, up, down, up, down) and make sure it stays the same throughout the whole movement.
In conclusion
Changing the rein across the long diagonal is trickier than it sounds!
Most of the problems that are experienced with this exercise happen because the rider fails to prepare for this deceptively difficult movement.
Remember that the first corner is very important. If you ride a poor corner your horse will be unbalanced and the movement will be inaccurate.
Lastly, if changing the rein across the long diagonal in rising trot, think about where you want to change your diagonal. Although riders are commonly taught to change their diagonal over X, it’s often more tactful to change it either before or after the diagonal line.
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