Scientific studies are helping us understand what dressage horses are capable of and how the demands of training and performance impact upon their health. Rachel Murray MRCVS looks at the evidence for guest editor Carl Hester

Guest editor Carl Hester says: “As dressage trainers we use all kinds of phrases to describe what we want to see horses doing with their bodies. We ask them to ‘lift the back’, ‘bend through the ribcage’ and so on.

“But from a veterinary viewpoint, can a horse physically do these things? And even if they’re physically possible, are they really good for the horse? I asked vet Rachel Murray to investigate…

“Riders are constantly asked by their trainers to translate dressage terms into improved quality of movement from the horse. But is the horse physically capable of what we are asking?

Recent work at the Animal Health Trust in Newmarket has given a greater understanding of the processes involved. Below are 7 common phrases we ask of our horses.

Phrase 1: ‘Do more transitions’

Changing from one pace to another requires the horse to use energy in braking or accelerating and altering the pattern of movement of his limbs. In a recent study investigating risk factors for lameness in dressage horses, we found that these transitions were protective against lameness. Why might that be?

In the wild, a horse makes a transition between paces at the most energy-efficient time. Yet the ridden dressage horse must change pace on command — and at a time when more energy is needed for muscle contraction. This means that transitions are hard work and result in a raised heart rate, so they’re good fitness training.

Changing from one pace to another also develops co-ordination, as he has to work out where his limbs are and keep his balance. But perhaps the most important aspect of a good transition is that the horse must maintain the correct posture. If done well, transitions activate the core musculature to flex the thoracic and lumbar spine.

Phrase 2: ‘Keep uniform bend through the whole body’

Scientific studies have shown that the horse has the ability to bend through his back, but not equally all the way along.

Maximum bend is possible through his neck and at the lumbosacral junction, just in front of the pelvis. For the rider, what may be more obvious as a bend is the attachment of the pelvis on to the spine and the shoulder blade on to the ribcage.

The shoulder blades are attached only by muscles, which allows them a large range of motion and enables the forelimbs to go a long way forward and back. The spine can rotate, allowing the ribcage to swing slightly from one side to the other. Where the pelvis attaches on to the spine it can also rotate to allow each hindlimb to come forward.

When these things all come together, one side of the horse becomes considerably shorter than the other — even though the actual amount of bend in the back itself is quite minimal and is largely concentrated in front of and behind the saddle.

Phrase 3: ‘Take more weight behind’

As training becomes more advanced, it appears that relatively more weight is taken on the hind limbs for an increased proportion of stride.

This requires core muscle strength to transfer the load from the limbs through the body. Generally, there is increased compression of the hock and extension of the fetlock when the hind limbs are on the ground.

In trot, the horse raises his ribcage through contraction of the muscles of the thoracic sling and flexes his back. In canter, he flexes and extends his back more than in trot, so he can more obviously “sit” by increasing lumbosacral flexion.

The stronger the muscles flexing the lumbosacral and hip joints, the more a horse appears to sit.

Phrase 4: ‘Come up in the wither’

As horses do not have collarbones, the forelegs are only attached to the body by muscles. This means that there is some flexibility in the attachment of the ribcage on to the forelimbs, as the trunk and ribcage are effectively hung in a sling from the shoulder blades (known as the thoracic sling).

If these muscles are contracted, the sling lifts up the trunk and ribcage relative to the forelimbs. The wither comes up and the horse actually becomes taller.

A horse working correctly learns to contract the muscles of the thoracic sling and come “up in the wither”. This is hard work when carrying a rider, so requires ongoing muscle strength and fitness training.

Phrase 5: ‘Come up in the back’

The weight of a rider makes a horse’s back drop (extend).

To counteract this weight, the horse must contract his abdominal muscles and those underneath the spine, which flexes the spine and brings the horse “up in the back”. This requires muscle strength and fitness.

A young horse inexperienced in carrying a rider, or a horse with poor muscle development, is likely to have a very mobile and unstable back. His spine may extend and his muscles may spasm in an attempt to hold everything in place, while his legs are trying to move underneath him.

If this extension is excessive, there is a risk of developing kissing spines.

Phrase 6: ‘Swing through the back in trot’

As trot is a gait using diagonal pairs of limbs, most of the movement of the spine is in rotation. To “swing through the back” the horse needs enough muscle stability to maintain back flexion and sufficient flexibility to allow this rotation.

This then allows the energy stored in the stretch of the flexor tendons while they are loaded on the ground to be transferred efficiently into taking the next stride.

Phrase 7: ‘Overtrack in walk’

Overtracking is when the hindlimb lands in front of the print of the forelimb.

In walk, a longer hindlimb stride occurs if the limb becomes longer through extension/flexion of the back and rotation of the pelvis. So a young horse with a very unstable, loose and flexible back is more likely to have a longer hindlimb stride with lots of overtrack.

But a horse trained correctly to grand prix level will have a very stable, well-muscled back. He is therefore likely to have less overtrack and a less extravagant walk.

Because of this stability and muscle development, his back moves through a smaller range of motion each stride.

The mechanics of motion

Biomechanics expert Hilary Clayton MRCVS says research is changing the sport of dressage — both in terms of understanding the horse’s performance and limitations, and with regard to the rules of how the gaits and movements should be performed.

“Slow motion and freeze-frame photography have revealed details of the horse’s locomotion that our naked eye is unable to appreciate,” says Hilary. “Using this technology, dressage paces and movements have been analysed in exquisite detail — sometimes revealing findings that differ from traditional beliefs.

“An early realisation was that, even though the movements of a diagonal pair of legs are synchronised, the hooves do not necessarily contact the ground simultaneously in either trot or canter. In trot, horses showing uphill balance tend to make contact with the hind hoof first, whereas a front-first sequence is often associated with being on the forehand.

“In canter, the diagonal footfall sequence differs according to the type of canter and stage of training.

“The rhythm of the canter pirouette strides has been a controversial topic. Slow motion analysis indicates a 4-beat rhythm, with the footfall of the inside hind preceding that of the outside front.

“If you see a pirouette photo with both hind hooves on the ground and both front hooves in the air, there can be no doubt that the canter has 4 beats.”

Challenging conventional wisdom

“Another area of discussion has been the presence — or not — of an aerial phase in piaffe,” continues Hilary.

“When slow motion studies of piaffe in Olympic competitors failed to show an aerial phase, the findings were not universally accepted.

“To investigate further, I made recordings of horses at the Spanish Riding School of Vienna. The result was the same: no aerial phase.

“From a biomechanical standpoint, this makes sense. In order to leap into an aerial phase the horse must extend [straighten] the joints of the hindlegs, which is not compatible with maintaining the lowered position of the croup that is required in a good piaffe.

“There is no doubt that science can further our understanding of dressage,” she concludes. “The findings are sometimes unexpected, however, and may challenge conventional dressage wisdom. We must stay open-minded if we are to learn from the research and use the information to benefit the sport.”