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Skeleton of the horse

The skeleton of the horse consists of a framework of bones combining to form a rigid support for the body mass and there movement, in response to the contraction of muscles and the consequent activation of joints provides locomotion.

The skeleton of the horse consists of

  • skull bones,
  • vertebrae, which form the spinal column,
  • ribs
  • a chest bone - 'sternum' - which is  attached to the 8 "true" pairs of ribs,
  • and bones in front and hind legs.

There is a lot to tell about the skeleton of the horse - and I invite you to thoroughly study this subject - but this article will focus on some details which are important in Straightness Training.

The spinal column of the horse

Straightness trainingThe first key of Straightness Training is about 'lateral bending' and it's a collective name that we use for everything that happens in the horse’s whole body to gain the ability to bend with the arc of the circle in both directions and  to bend the body in lateral movements.

In lateral bending the body appears to bend evenly in the spine, from his poll to his tail, but anatomically seen that is not possible.

The spinal column can bend to the left and to the right, but is not flexible throughout the length of the spine because of the vertebrae:

  • Part 1: 7 neck vertebrae: most flexible part of the spine, so the horse can very easily bend his neck. The neck also easly ‘overbends’, which means that the neck is not aligned with the body.
  • Part 2: 18 chest vertebrae: relatively stiff area because of connection with the ribs. The first 8 pairs of ribs are connected to the top of the first 8 chest vertebrae and at the bottom they are connected to the sternum. And not a lot more flexibility can be expected from the other 10 vertebrae and 10 ribs. So there’s limited flexibility in the chest area.
  • Part 3: 6 lumbar vertebrae: more flexible, because there is no connection to the ribs, but there is limitation because of the large transverse processes. They would hit each other if there was too much sideways movement,
  • Part 4: 5 connected croup vertebrae, this area is not flexible because the vertebrae are united in the sacrum.
  • Part 5: 15-20 tail vertebrae, and the tail will generally hang to the left when the horse turns to the left and to the right, when he turns to the right.

So the flexibility of the spine differs in each part. How much an area (neck, chest, behind the saddle, area of the pelvis, tail) can bend, depends on the shape of the vertebrae (body, spinous process) and the construction (connected to ribs or other vertebrae or not)

The neck is the most flexible part (1), followed by the lumbar region (3). Bending in the rib area (2) is hardly possible and the croup vertebrae (4) are connected and cannot bend at all.

Therefore some vertebrae and parts of the spine also need to rotate and flex when riding circles and lateral movements.

Spinal movement

Movements of the spine can be measured in three dimensions by setting up three axes: x, y, z.

Depending on their location and construction a vertebra will move in three different directions:

X: Extension/flexion  

Y: Rotation

Z: Lateral Bending  

All three types of movement - extension/flexion, rotation and lateral bending - occur in each part of the spine and there has been a fair amount of research done to figure out how much motion there is all three directions in different regions of the spine.

But before we dive into this research and in these three dimensions, let's first dive a bit into the history of lateral bending.

History of the 'lateral bending'

Gustav Steinbrecht (1808–1885) wrote in his book 'The Gymnasium of the horse' a lot of chapters about 'bending'.

In the original - German - version of the book, there are the following chapters in the book:

  1. Bending of the neck
  2. Bending of the poll
  3. Bending of the rib cage
  4. Bending of the back
  5. Bending of the hindlegs

In chapter 3 he discusses the chest area - the area of the ribs - and chapter 4 is about the lumbar area - the area behind the saddle.  Nowadays, in the English version of the book chapter 3 and 4 has been combined to 'Bending of the spine', but it's interesting to see the original chapters in the spirit of age:

Steinbrecht speaks a whole chapter about 'bending of the ribs' and 'bending of the rib cage' and what he means by that is pushing the ribs close to each other on the concave side due to bending of the spine.

He writes (translated from the original German book):

"The correct and well founded bending of the rib cage or lateral bending of the back vertebrae is a main characteristic of a well ridden horse...

... it forms the the soul of the art of riding...

... As a part of the spine, the back vertebrea must be bend laterally according to the same rules as the neck vertebrae, but working them is easier because they are more fixed by the rib cage and therefore have less of a tendency to bend incorrectly and in an exaggerated manner."

So here he describes the bending that he 'sees', but what he 'feels' is the combination of bending, rotation, and flexion (XYZ) in that area:

"The rider recognizes the correct, well founded rib cage bending immediately by his secure, comfortable seat with a slight, natural tendency towards the inside...." and d a few sentences later he writes about "... the tendency of the rider to hang inward, keeping both bodies in harmony and simultaneously match the laws of centfigal forces on curved lines...". 

Over the years, science has brought new light to spinal movement: the horse 'appears' to bend evenly from head to tail, but nowadays reseach has proven that this is anatomically seen not possible because of the difference in flexiblity in all areas of the spine. Also rotation and flextion is needed to create the 'illusion' of lateral bending.

However, 'lateral bending' is still the most useful image and metaphor for rider and trainers, because when the horse 'feels' and 'looks' as if the horse is evenly bended from head to tail, he turns in a balanced way.

Research on lateral bending

Many 'tests' have been done with horses to figure out how a horse use their spine in turns and on circles and many equestrian books have a topic about bending:

  • Some of the research is done on dead horses where they can measure extremes. Other research looks at horses alive and how they move naturally.
  • Some of the research is done on one single horse, other research focuses on a group of horses, some of the research used race horses, other dressage horses, some research in walk, other in trot or canter. (For example "Six thoroughbred horses (mean age 9.6 years) cantered on a treadmill at four velocities".)
  • Sometimes the amount of movement between two vertebrae is mentioned, in other research the movement of a single vertebra is observed in 3D.
  • Sometimes the research is done with uneducated (natural asymmetrical) horses, other research with educated (straightened) horses.
  • Sometimes the research is done with big warmbloods with long backs, other research with smaller horses with short backs.
  • Some of the book describes a theory on bending/rotation based on riding a horse with steady rein contact on both reins, other books base their theory on riding with a supple/soft inside rein and contact on the outside rein.
  • Some of the books describe the proces based on horses on the longe with side reins, other base their work on horses at liberty.

So with scientific research and written materials it’s always important to realize on what grounds the results are based.

Totally other outcomes may be expected if other types of horses are used, or even more important, if the rider uses a totally different training style. Because it makes a huge difference in influence on the spinal movement, if a rider rides with strong contact on both reins or if the rider has a soft inside rein, or if the horse moves with side reins or not. It also makes a huge difference if a rider is riding 'on the bit' (picture) or 'behind the vertical' or 'against the hand' or 'towards the hand', all four styles will influence the movement of the spine differently. Also the asymmery of the rider in his own pelvis and spine and where he has his center of mass will be of influence, as are many, many other factors.

It's important to see each research, book, and article within it’s context. And we have to realize that not all research is reliable or reproducibly: sometimes the same research is done with a completely other outcome than the original.

It’s like when somebody is baking a fantastic lava cake and somebody else wants to bake the same cake. He asks this amazing cake baker what he needs: the ingredients, the recipy, the materials, the brand of the oven, the heat. Now 100% equal the cake will never be, but when it’s close, it’s a good sign. If the result is different – then there are several conclusions possible: the second cake baker did something wrong, or the amazing cake baker didn’t explain it well, or, and that’s the most interesting: the amazing baker didn’t understand completely how he created the awesome cake in the first place...

The absolute truth or an opinion?

There’s a whole spectrum between ‘the absolute truth’ and ‘just a theory or opinion’, and it’s always important to keep this spectrum in mind regarding interpreting research, books and materials.

Results of research are often reported in inches/centimeters, percentages and number of degrees, which are sometimes presented as ‘the absolute truth’. But sometimes the results differ and also books and articles on the internet are not always agreeing:

  • Sometimes the results state that the maximum possible bending in the whole spine is 15 cm, other results state 18 cm.
  • Sometimes the results state that the greatest amount of rotation was measured in the chest area at the level of the 11th and 12th chest vertebrae joint, other results measure an decreased rotation from the 9th until the 14th. Another source states that the biggest rotation is at the 18th chest vertebra, because that vertebrae is connected to the lumbar region, and the rotation in the lumbar vertebrae is greater than in the chest, because the tilt from the pelvis and sacrum, caused by the stepping under of the inside hind leg, is transmitted forward along the spine through the sacrum, to the lumbar vertebrae, to the chest vertebrae.
  • Some materials state that the chest vertebrae have to rotate outwards in the turn, other materials state that the chest vertebrea have to rotate inwards.
  • Some materials talk about specific 'S shaped' horses where head and neck are bended in one direction and the chest area in the other direction – so the chest vertebrae rotates in the opposite direction, not corresponding with the neck bending. Other materials state that every horse is 'S shaped' by nature: 'left bended' horses are left bended in the neck and rotates to the right in the chest, (and vice versa with right bended horses). So they state that all horses have a preferential chest rotation one way and they will choose to rotate that way no matter which direction they go. So wheather the neck bends to the left or right, the chest area keeps rotating in the an equal way to both sides.

Now just to be clear, this post is not meant to 'find the truth', or to dive into detailed scientific discussions, this post is just meant to give the ‘bigger picture’ and to realize that there are different 'beliefs’, but that we have to be careful with making generalisations. Remember the story of the scientists:


Five scientists sit on the train and travel through Scotland. They look out the window and see a sheep in a pasture.

  • Scientist #1 says: All sheep are white.
  • Scientist #2 says: No, all sheep in Scotland are white.
  • Scientist #3 says: No, all sheep in this pasture are white.
  • Scientist #4 says: No, this sheep is white.
  • Scientist #5: we can say with certainty that this sheep is white on this side.

So just observe your individual horse, that has a certain breed, age, condition, education, a horse that you ride in a certain discipline, in a particular style of using the reins, a horse that you ride with your amount of weight, suppleness, asymmetry etc. etc. and just observe what is happening when you ride on circles. Then whatever is out of balance, see it as a challenge and change your approach to turn things around.

The skeleton in LFS

So the movement of the back is very complicated, the map is never the territory, in practice the spine moves in a three dimensional way when we ask our horse on a circle.

Besides Lateral bending - key #1 in Straightness Training - we also strive for a Forward-down tendency in head and neck - key #2 - to encourage the stretch of the whole topline and we focus on Stepping under of the inside hind leg - key #3. All keys are closely connected, and one key cannot without the other keys.

So to get into a forward down tendency, we need the lateral bending of the horse, so the back muscles will stretch in both ways, which encourages the lengthening of the topline. Now because the lateral bending of certain spinal areas is limited we also need rotation. And a proper lateral bending also requires engagement of the hind legs.

So let's see what happens in the horse's skeleton when we invite the horse to move in LFS on the circle:

Part 1 - the neck vertebrae:

  • Extension/flexion are maximal at the joint that connects the head to the first neck vertebra and because of this joint the horse can shake his head as if he is saying ‘yes’ and this ability allows a horse to go for example too much behind the vertical during the work. We strongly focus on forward down, because the higher the head and neck are carried the shorter the strides in behind.
  • Lateral bending is relatively uniform along the length of the neck and the horse can easily overbend his neck.
  • The first two neck vertebrae have far more ability to rotate as the other five: that’s why a horse can tilt and twist the head during the work. The horse might start to tilt the head if the inside hind leg is not stepping under well, so again, what happens on one end of the spine often relate to and influences what happens on the other end and in between.

Part 2: the area of the chest and ribs

  • Extension/flexion takes place at the chest area and it’s about the rounding and hollowing of the back. When a horse carries a rider with a hollow back, kissing spines may arise, because the spinous processes, which look like shark fins, might start to kiss each other. So in ST we encourage the forward down tendency when riding a horse at all times.
  • When it comes to the lateral bending, the chest area of the spine is limited in the ability to bend because of the connection to the ribs. So lateral bending is always accompanied by rotation in the chest area.
  • Overbending of the neck can disturb proper rotation in the chest: when the rider overbends the neck of the horse, in combination with a shift of the center of mass to the outside shoulder (falling over the outside shoulder), the chest vertebrae might rotate in the opposite direction and then rider and saddle often slide to the outside of the horse’s back.

Part 3: the lumbar area (part behind the saddle)

  • The connection between the last lumbar vertebra and the sacrum is, after the neck, the most flexible when it comes to flexion and extension of the back. You can see that very clearly in the sliding stop, where the horse tilt his pelvis to the max.
  • Because of the combination of bending and rotation of the lumbar vertebrae, the horse is able to produce the haunches-in.

Part 4: the sacrum (area where the hind legs connect to the spine)

  • The sacrum consists of 5 connected vertebrae, so it cannot bend, only rotate. The hind legs are connected to the pelvis which is connected to the sacrum. Via this connection, this joint, the energy that starts in behind is transferred through the spine towards the front. Now when a horse moves, you see that his pelvis tilts from side to side depending which leg is on the ground. This up and down movement is transmitted through to the sacrum to the lumbar vertebrae and then to the chest area.

The hind legs contribute to a correct lateral bending of the whole body, when the inside hind leg is able to step under the center of mass: this will bring the inside hip forward, and then the lateral bending of the whole body is also triggered from behind.

The stepping under of the hind leg will also result in a bending of the haunches and a closing of the angles between the joints when we put more weight on it.

A joint is a movable connection between two bones and the hind leg contains seven joints:
Skeleton<br<br /> /> of<br /> the<br /><br /> horse
1. the lumbo-sacral-joint, which connects the spine with the hind legs
2. the hip joint
3. the stifle joint (pronounced st-eye-full joint)
4. the hock joint
5. the fetlock joint
6. the pastern joint
7. the coffin joint

So the hind leg has many joints, which make it resemble an 'accordion' or a 'spring'. This gives a good bending and carrying potential to the hind leg.

The goal of Straightness Training is a 'riding balance', in which 3/5 of the body weight is carried by the hind legs to enlighten the fragile front legs.

Skeleton<br<br /> /> of<br /> the<br /><br /> horse



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