Reducing the pressure - Scientists discover performance benefits of relieving five key pressure points under tack

By Dr Russell Mackechnie-Guire

Scientists discover performance benefits of relieving five key pressure points under tack

Recent scientific studies reveal how using new designs of saddle, pad, girth and bridle can significantly benefit the locomotion of the galloping racehorse

Researchers detected peak pressures under commonly used tack that were of a magnitude high enough to cause pain and tissue damage. When horses have to manage this type of discomfort on a daily basis, they develop a locomotor compensatory strategy. Over time, this can lead to tension and restriction that inevitably affects performance. Physio interventions will usually ease the symptoms of tightness and soreness and, after a period of rest, performance may be restored and improved. However, this costly course of action only addresses the secondary problem. If the primary cause is still apparent—in this case pressure from badly designed or ill-fitting tack—the compensatory gait strategy will be adopted again, the tension will return, and the cycle will repeat.

Reducing the pressure that forces a horse to adopt a compensatory gait will not only improve performance, but it will also help prevent further issues which could have veterinary implications and reduce susceptibility to injury in the long term.

Saddle up

When scientists tested the three most commonly used exercise saddles, they discovered every saddle in the test impinged on the area around the 10th-13th thoracic vertebrae (T10-T13)—a region at the base of the wither where there is concentrated muscle activity related to locomotion and posture. The longissimus dorsi muscle is directly involved in the control and stabilisation of dynamic spinal movement and it is most active at T12 (see fig 1).

Dynamic stability is the combination of strength and suppleness—not to be confused with stiffness—and is essential for the galloping thoroughbred. The horse’s back moves in three planes: flexion-extension, lateral bending and axial rotation—all of which can be compromised by high pressures under the saddle (see fig 7).

Studies in sport horses have shown that saddles which restrict this zone around T13 restrict muscle development and negatively influence gait. This effect is amplified in a racehorse because they train at higher speeds, and faster speeds are associated with higher forces and pressures. In addition, gallop requires significant flexion and extension of the horse’s spine; and if this is compromised by saddle design, it seems logical there will be an effect on the locomotor apparatus.

Tree length

In addition, half-tree and full-tree saddles were shown to cause pressure where the end of the tree makes contact with the horse’s back during spinal extension at gallop. In the three-quarter-tree, high pressure peaks were seen every stride and either side of the spine, correlating with the horse’s gallop lead; this indicated that the saddle was unstable at speed (see fig 1).

Using a modified saddle design to achieve a more symmetrical pressure distribution, researchers saw a positive impact on spinal stability and back muscle activation. The hindlimb was shown to come under the galloping horse’s centre of mass, leading to increased hip flexion, stride length and power. A longer stride length means fewer strides are necessary to cover any given distance; and better stride efficiency brings benefits in terms of the horse’s training potential and susceptibility to injury (see compensatory strategy panel).

Pressure pad

The saddle pad acts as a dampening layer between the horse and the saddle, reducing pressures and absorbing forces. In a pilot study of thoroughbreds galloping at half speed over ground, a medical-grade foam saddle pad was shown to be superior at reducing pressure, significantly outperforming gel and polyfill pads. Preliminary findings show the forces were 75% lower, and peak pressures were 65% lower under the foam pad than those recorded under the gel pad. The polyfill pad reduced the forces and peak pressures by 25% and 44%, respectively, compared to the viscose gel pad.

A pad with a midline ‘seam’ designed to follow the contour of the horse’s back and withers performed best, maintaining position and providing spinal clearance even at speed. Flat pads without any shaping or a central seam were observed to slip down against the spine as the horse moved, even when the pads were pulled up into the saddle channel before setting off. The pressure associated with a pad drawing down on the spine under the saddle will lead to increased muscle tension, reduce elasticity of the back and could potentially alter gait. Relieving pressure at this location improves posture, movement and propulsion.

It might be assumed that using multiple pads under an exercise saddle would improve spinal clearance or comfort. However, based on studies, this is not the case. …

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How technology can quantify the impact saddles have on performance

By Dr. Russell Mackechnie-Guire

Thanks to advances in technology, it is getting easier for scientists to study horses in a training environment. This, combined with recent saddlery developments in other disciplines, is leading to significant progress in the design and fit of exercise saddles.

Back pain, muscle tension and atrophy are common issues in yards. Although there are many contributory factors, the saddle is often blamed as a potential cause. Unlike other equestrian sports, where the effect of tack and equipment on the horse has been investigated, until now there has been little evidence quantifying the influence of exercise saddles.

New era

The technological advances used in sport horse research are sparking a new era in racing, enhancing our understanding of the physiological and biomechanical demands on the horse, and helping improve longevity and welfare. For the trainer this translates into evidence-based knowledge that will result in marginal or, in some cases, major gains in terms of a horse’s ability to race and achieve results. Race research has always been problematic, not least due to the speed at which the horse travels. Studies have previously been carried out in gait laboratories on treadmills, but this is not representative of normal terrain or movement. Thanks to new measuring techniques, we can now study the horse in motion on the gallops. Evidence of this new era arises from a recent study published in the Journal of Equine Veterinary Science. It found areas of high pressures under commonly used exercise saddles which had a negative influence on back function, affecting the horse’s gallop and consequently performance. 

The pressure’s on

Researchers used a combination of pressure mapping and gait analysis (see Technology in focus panel) to investigate three designs of commonly used exercise saddles: full tree, half tree and three-quarter tree. The aim was to identify pressure magnitude and distribution under each of the saddles then to establish whether the gait (gallop) was improved in a fourth saddle designed to remove these pressures. 

Areas of high pressure were found in the region of the 10th-13th thoracic vertebrae (T10-T13). Contrary to popular belief, none of the race exercise saddles tested in this study produced peak pressure on or around the scapula. The pressures around T10-T13 at gallop in the half, three-quarter and full tree were in excess of those detected during jumping or dressage in sport horses. They were also higher than pressures reported to be associated with clinical signs of back pain. Therefore, it is widely accepted that high pressures caused by the saddle could be a contributory factor to back pain in horses in training.  

Three most commonly used saddle-tree lengths, plus the new design (purple 40cm)

Half tree: High peak pressures in the region of T10-T14 were consistent with the end of the tree.

Three-quarter tree: Peak pressure was localised on one side of the back at a time, depending on the horse’s gallop lead.

Full tree: Peak pressure was further back and, although not high, gait analysis demonstrated a reduction in the extent to which the hindlimb comes under the horse, reducing the power in the stride.

New design: A more uniform pressure distribution, recording the lowest peak pressures at each location.

Lower pressure leads to longer strides

When looking at propulsion, there are two important measurements: the angle of the femur relative to the vertical and hip flexion. When pressures were reduced beneath the saddle, researchers saw an increased femur-to-vertical angle in the hindlimb and a smaller hip flexion angle (denoting the hip is more flexed).

A greater femur-to-vertical angle indicates that the hindlimb is being brought forward more as the horse gallops.

A smaller hip flexion angle denotes the hip is more flexed, allowing the horse to bring his quarters further under him and generate increased power.

Improved hip flexion was recorded in the new saddle design (A) compared to a commonly used saddle (B).

When pressure is reduced in the region of T13, the hindlimb is allowed to come more horizontally under the horse at this point in the stride, leading to an increase in stride length. Researchers speculate that this could be due to the fact that the thorax is better able to flex when pressure is reduced.

Perhaps surprisingly, the study found that reducing saddle pressures did not result in any significant alteration in the forelimb at gallop. The major differences were recorded in hindlimb function. This could be explained anatomically; the forelimb is viewed as a passive strut during locomotion, whereas the hindlimbs are responsible for force production.

This is consistent with findings in the sport horse world, where extensive research investigating pressures in the region of the 10th-13th thoracic vertebrae has shown that reducing saddle pressure is associated with improved gait features in both dressage and jumping. 

Speed matters…

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