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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Saddle + Half Pads - The effect on race saddle pressures and gallop kinematics

By Dr. Russell Mackechnie-Guire

Scientific research quantifies the impact different pads have on the horse’s performance

The use of pads under the saddle has been common for years, but now scientists are using dynamic testing technology to discover how well they really work

In everyday yard situations where multiple horses use the same saddle, putting one or more pads under has been seen as a way of providing cushioning and comfort for the horse, or even relieving pain. However, there has never been any research in racehorses to demonstrate whether this reduces saddle pressures or provides comfort. Furthermore, there is limited scientific evidence to suggest which type of pad is most effective.

A recent study suggests that, depending on the material and design, using a pad beneath the saddle might not always achieve the desired pressure-relieving effect. And using multiple ineffective pads under the saddle might not only be a waste of time and money, but it could potentially cause areas of high pressures, compromising the horse’s locomotor apparatus and affecting race performance.

Peak pressure of more than 35kPa were recorded in two of the three pads.

Peak pressure of >35 kPa can cause compression of the capillaries, leading to soft tissue and follicle damage (ischemia) which, in extreme or prolonged cases, results in white hairs, muscle atrophy, skin ulcerations and discomfort.

A recent published study evaluated saddle pressure distribution in sports horses using pads made from sheepskin, viscose gel and a medical-grade closed-cell foam. When using a gel pad, the peak and mean pressures increased in the front region of the saddle in trot and canter. This is possibly due to the gel’s lack of ability to dissipate shear forces compared to wool or foam.

Similar findings were seen in a pilot study of thoroughbreds galloping at half speed over ground. The same dynamic testing was used (see Technology & Anatomy panel) to compare the forces and peak pressures under polyfill pads, as well as viscose gel and medical-grade closed-cell foam. From the initial trials, the overall forces recorded were significantly higher than those seen in the sports horse study. This seems reasonable, given the difference in locomotion and speed (see Speed & Force panel).

Preliminary findings show the forces were 75% lower, and peak pressures were 65% lower under the medical-grade closed-cell foam pad than those recorded under the gel pad. Interestingly the polyfill pad, which deforms to the touch, reduced the forces and peak pressures by 25% and 44% respectively compared to the viscose gel pad.

The role of the pad is to act as a dampening layer between the horse and the saddle, reducing pressures and absorbing the dynamic forces which occur during locomotion.

Based on findings from the sports horse study, and initial findings from the racehorse study, it appears that the medical-grade closed-cell foam pad is superior in its effectiveness at acting as a pressure-reducing layer between the saddle and the horse.

Pressure to perform

A shaped saddle pad with a midline seam is less likely to draw down on the spine

Reducing saddle pressures improves gallop locomotion. Horses will still perform when asked, despite areas of high pressures induced by the saddle and pad; but they develop a compensatory locomotor strategy in an attempt to alleviate any discomfort.

To increase speed, a galloping horse will either increase stride frequency or increase stride length. Both mechanisms can be used, but the horse will have a natural preference. Published pressure studies have shown that stride length is increased when saddle pressures are reduced. Now, new research is underway quantifying whether a stride frequency approach, which has higher peak forces, could be a compensatory strategy in response to discomfort caused by pressure.

Forces are influenced by speed and weight and are produced when the hoof comes in contact with the ground. At racing speeds of 38 mph, the hoof hits the ground approximately 150 times a minute. Stride frequency is an important consideration because a study has suggested that horses have around 100,000 gallop strides before the soft tissues fail. Therefore, any reduction in loading cycles (number of strides) could potentially help reduce injury risk.

Harder, faster, longer

Every stride impacts the horse’s joints, causing wear and tear (see Speed & Force panel), so fewer longer strides is the preference for optimum training efficiency. Although horses have a naturally imprinted option, the pressure studies demonstrate that they switch between the two in response to certain extrinsic factors, such as high saddle pressure.

Our task as trainers is to optimise the horse’s locomotor efficiency by removing any impediment that might force it to adopt the shorter-stride compensatory gait. We speculate that equipment which increases pressure (such as an unsuitable design of saddle, bridle, girth or saddle pad) will be counterproductive because it may encourage an increase in stride frequency and compromise natural locomotor efficiency.

Contouring is key

In both studies, the saddle pads that were designed to follow the contour of the horse’s back and withers performed better than those that were flat with no shaping. Furthermore, pads with a midline seam connecting the two sides were able to maintain traction and position, providing spinal clearance even at speed.

In contrast, pads that were flat without any contouring or with no central webbing seam were observed to slip in response to the horse’s movement, drawing down against the spine under the saddle. This was seen even when the pads were pulled up into the saddle channel before setting off.

Quality vs quantity

In an attempt to improve comfort, it’s standard practice to use multiple pads under an exercise saddle. However, adding more shapeless padding can lead to instability and potentially saddle slip.

This feeling of instability can encourage the jockey to overtighten the girth in an attempt to keep the saddle still. One study demonstrated a relationship between increased girth tension and a reduced run-to-fatigue time on a treadmill, indicating that girth tension can affect the breathing of the galloping horse.

In addition, bulk under the saddle puts a feeling of distance between the horse and rider. This compromises the close contact feel and balance all jockeys strive to achieve and hinders the lowering of the jockey’s centre of mass relative to the horse.

Age concern

It’s worth noting that the ability of a material to absorb pressure can be significantly compromised with use and washing, as well as changes in climate. As some materials age, they degrade and loose any initial shock-absorbing qualities. For example, wool loses its ‘crimp’ over time and becomes less effective, so a well-used wool pad may not absorb as much pressure as a new one. …

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The benefit of using ‘yearling rollers - Dr. Russell Mackechnie-Guire asks if a roller is a harmless piece of equipment? -scientists discover performance inhibiting spinal pressure under rollers

Dr. Russell Mackechnie-Guire

Reducing pressure under the saddle, bridle and girth has been found to significantly improve performance, and now the roller has been scientifically tested.

Lost training days, treatment and medication for back problems are time consuming and costly, so optimising equine spinal health from early on is an essential consideration in improving equine health and welfare. When a young horse is started, one of its first experiences is to have tack on its back, initially a lungeing roller. The roller, a seemingly harmless piece of equipment and its effect on the horse, has previously been overlooked. However, it has now come under scientific scrutiny by the same research team that investigated the impact of pressure distribution under the saddle, bridle and girth on equine health and performance.

Their recent study used high-tech pressure mapping to examine the pressures exerted on the horse’s back during lungeing (see technology panel). Localised areas of high pressures were consistently recorded under the roller on the midline of the horse’s back directly over the spinous processes in the region of the 10th and 12th thoracic vertebrae (T10-T12, see anatomy panel).  

High pressure directly in this region, as seen under a conventional roller, is likely to cause the horse to seek a compensatory locomotor strategy and adopt a posture where the back is stiffened and hollowed, resulting in an extended spine. Previous research has shown that back function and gallop kinematics are compromised by a stiffened spine.

Studies have demonstrated that pressure-relieving modifications in a saddle result in increased stride length and hip flexion, along with a greater femur-to-vertical angle (indicating that the hindleg is being brought forward more as the horse gallops). Reducing saddle pressures leads to a marked improvement in the horse’s locomotion, allowing it to gallop more efficiently. 

A modified roller that removes pressure will allow the back to function without restriction.

The roller is positioned over the part of the back where the front half of the saddle sits; by applying these principles, modifying the roller to remove pressure would allow unhindered back function. 

The equine back is an essential component of the locomotor apparatus, transferring biomechanical forces from the hindlimb. So, a modified roller will not only result in improved locomotion and performance but will also have long-term spinal health benefits.

Strong start

In racing, where lungeing is primarily used prior to backing, what we do to and the equipment we use on the young horses in the preparatory stages are likely to have a significant impact on the development of the horse’s posture, back health and locomotion. 

If a young horse begins the training process of being lunged with a roller that exerts pressure directly on the spine at T10-T12, it will develop a strategy to compensate for the discomfort. Then, as the horse progresses to a saddle—which similarly exerts high pressure in the same area—it is inevitable that this will have an effect on the locomotor system. The horse’s athletic performance will be significantly compromised before it even gets on the track. 

Innovative pressure-relieving modifications in tack design have demonstrated improved locomotion when pressure is reduced. Identifying and replacing any equipment that has limiting effects on locomotion or development could have long-term benefits for the longevity and performance of the horse. This applies particularly to the lungeing roller as it is the first piece of tack a youngster has on its back. It is essential that the horse does not develop a locomotor strategy to compensate at this stage.

Under pressure

Pressure mapping during lungeing

Conventional roller - 35kPa pressure directly on the spine at T10

Conventional roller & side reins - pressure consistent at T10 but increases at T11 and T12 to 45kPa

New roller design, even with side reins - all pressure is removed from the spine]

In a recent study, horses were lunged on a 20-metre circle on both reins in trot and canter wearing a roller fitted with pads. In canter, peak pressures were seen each time the inside forelimb was in stance (on the ground). In trot, pressure peaks occurred each time a forelimb was in stance phase. 

Given that the horse is experiencing high pressures under the roller directly on the spine in the region of T10-T12 in every repeated motion cycle (stride), it is inevitable that a compensation strategy will develop.

When trotting and cantering with no attachments, such as side reins or training aids, peak pressures under the centre of the roller were found to be similar to those seen under the saddle with a rider on board. Studies have shown pressures over 30kPa can cause back discomfort. In this study, researchers measured pressures up to 35kPa directly on the midline of the horse’s spine, in every stride, with just a roller and pad.

With side reins attached, the location of the peak pressure was brought further towards the front edge of the roller. Essentially, the pull of the side reins caused a ridge of pressure under the front half of the roller, and the readings increased to 45kPa.

Compensation costs

Compensatory gait strategies lead to asymmetric forces which have a negative effect on limb kinematics (movement). The consideration here is that the horse is experiencing these locomotor compromises before the back has been conditioned to manage the increased forces, and before a jockey has even sat on its back. 

It remains to be shown whether the compensatory gait and asymmetric forces caused by early roller pressure manifest as lameness or loss of performance later on. There is a coexisting relationship between back problems and limb lameness, but evidence is still being gathered as to which one comes first. Researchers are investigating to what extent loss of performance and lameness issues might be traced back to these ‘training and backing’ experiences. It is therefore essential that young horses are started with correctly fitting equipment to limit any long-term effect.

Lungeing for rehab

In addition to the backing process, lungeing also occurs during other influential periods of a horse’s life, including rehabilitation after surgery. Post-operative recommendations for kissing spines can often include lunge work with training aids to induce spinal flexion and opening up of dorsal spinous processes. …

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On the bridle - scientific research uncovers performance advantages of different types of bridles - reducing bridle pressure

By Dr. Russell Mackechnie-Guire

Using a modified bridle design has a significant impact on whole horse locomotion–front and hindlimb–not just the head. 

Recent scientific advances have seen an increase in performance-based research, particularly in the sport horse world where a podium finish can depend on the smallest of margins. The findings from the sport horse research can be translated to the racing thoroughbred where the shortest distance can put you first past the post. All items of training tack and equipment have found themselves under scientific scrutiny, with some unexpected results which could have significant effects on racehorse performance. 

Perhaps one of the most surprising discoveries was the effect that bridle fit and design has on the locomotor apparatus of the horse (biomechanics). The bridle is a neglected item of tack which has, until now, received little scientific attention.

Ahead of the game

As well as improving locomotion these findings could have a significant benefit when it comes to resolving common issues affecting race performance, such as oral lesions in the commissures (corners) of the lips, tongue lolling and hanging, as well as steering or control issues.  

A sensor mat was used under many different bridles and nosebands to measure and record pressure on the horse’s head in motion.]

Research indicates that these behaviours are likely to occur as a result of the horse seeking relief from bridle pressure and instability. Tongue ties or Australian nosebands are two examples of gadgets traditionally used to remedy these issues, but they have their own welfare and pressure-inducing concerns. A more effective solution would be to remove the primary cause of discomfort which leads to the negative or undesirable behaviour by using a modified pressure-relieving bridle design.

Pressure head

Research using a calibrated pressure sensor mat, which was positioned beneath all parts of the bridle, revealed interesting findings and disproved some long-held assumptions. 

It had long been thought that horses experience bridle pressure directly on their poll. In contrast, the research team found no significant areas of pressure over the poll. Instead, areas of high peak pressure were located at the base of the ears in the region where the browband attaches to the headpiece. Anatomically this corresponds to the temporomandibular joint (TMJ). The TMJ is an essential part of the physiological apparatus, associated with the swallow reflex and the hyoid apparatus (see anatomy panel). The location of pressure (base of the ear and TMJ) was consistent in all commonly-used headpieces and occurred at the same moment in the stride, regardless of the make or design. 

Important locomotor muscles are all linked to the mouth and tongue via the hyoid.

The research team also used gait analysis where markers are placed on the horse’s anatomical locations (joints), allowing locomotion to be measured. …

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How girths have been scientifically proven to have an impact on performance

By Dr. Russell Mackechnie-Guire

Groundbreaking research has revealed the effect girths can have on the locomotion of the galloping racehorse.

Generally, whenever the subject of tack and equipment is discussed, the saddle is always the first, and possibly even the only, consideration. Recent scientific studies have revealed interesting findings relating to girth design and its association with gallop kinematics (movement). These findings could bring significant benefits for trainers—in terms of performance and equine health.

It seems the girth has the potential to be more influential and important than ever been imagined. Indeed, the girth’s impact on equine locomotion has been reported to be so great that authors of a study suggest the girth and its fit should be considered by a veterinarian when evaluating a horse for poor performance.

Thanks to advances in technology, we have enhanced our understanding of the physiological and biomechanical demands placed on the horse. This evidence-based knowledge is leading to progress in the development of race and exercise tack, allowing trainers to optimise benefits brought about by the design and fit of saddles and girths—benefits which have been quantified using scientifically robust principles and state-of-the-art measuring systems.

Pressure matters

The association between saddle pressures and back discomfort is a topical area within the equine literature. Studies have reported that a mean saddle pressure of more than 13kPa, or peak pressure of more than 35kPa, has the potential to cause ischemia—compression leading to soft tissue and follicle damage. This can result in the appearance of white hairs, muscle atrophy and skin ulcerations, with the potential to induce discomfort. 

It has always been assumed that girth pressures are at their highest on the midline of the horse’s trunk, at the horse’s sternum (breastbone) where the girth passes over the bone. In a study investigating girth design on sport horse performance, researchers identified repeatable high pressures beneath the girth, but these pressures were actually located behind the elbow, not on the sternum. This also seems logical, given it is the location where girth galls and girth pain may appear.

Adapting technology previously used in saddle-based research, using a pressure mat with 256 individual pressure sensor cells, researchers were able to quantify the precise levels and exact location of actual pressures beneath the girth. For the first time, they were able to demonstrate how the pressure distribution changes during locomotion and show that the pressure peaks are directly associated with the timings of the gait. 

Limb kinematics were quantified using a two-dimensional motion capture system. The combination of pressure mapping and gait analysis demonstrated that a girth designed to alleviate pressure, particularly in the region behind the elbow, resulted in an improvement in equine locomotion and the horse’s movement symmetry.

Two-dimensional motion capture is used to quantify improvements in gait.]

Speed increases pressure

The groundbreaking findings from the sport horse study sparked further investigation into racing thoroughbreds. It is accepted that high speeds are associated with higher pressures under the saddle and, applying the same principles to a girth, it was speculated that girth pressures may increase with an increase of speed.

In a recent experiment, researchers quantified girth pressures in a group of racehorses that were galloping on a treadmill at a standardised speed wearing commonly-used exercise girths. All girths were of the same length and tension. Just as in the sport horse study, increased girth pressures were identified behind the elbow in the galloping thoroughbred, with pressure peaks occurring when the forelimb opposite to the leading leg was in stance (see photo).

The moment in the stride when peak pressure is seen—the point where the musculature is trapped between the front of girth and back of leg.]

Although the location of pressure was consistent between sport horses and racehorses, the magnitude of the pressures recorded under commonly used race girths was dramatically higher—and far higher than had been reported in any previous saddle study. The girth pressure mat was calibrated to manufacturer’s guidelines at a maximum of 106kPa, but in the racehorse study pressure values for a galloping horse wearing a regular girth peaked out above the highest calibration point. It was not possible to estimate the exact magnitude of girth pressure, but it is worth noting that 106kPa is already three times the peak pressure reported to cause capillary damage and discomfort beneath a saddle.

Pressure under a straight girth on a horse galloping on a treadmill was higher than the pressure mat could record.

In the second part of the experiment, the same horses were galloped over-ground in order to quantify gallop kinematics and determine if there was any change when girth pressures were reduced. Data demonstrated that a modified girth, designed to avoid areas of peak pressures, significantly improved the horse’s locomotion at gallop with increased hock flexion, hindlimb protraction and knee flexion. 

Space to breathe

Girth pressures are also thought to have an influence on the horse’s capacity to breathe efficiently. One study demonstrated a relationship between increased girth tension and a reduced run-to-fatigue time on a treadmill, indicating that girths can affect the breathing apparatus of the galloping horse. 

The more recent girth pressure study also identified a relationship between peak pressures in a normal girth and breathing. This study didn’t quantify respiration rate, but visual observation of the pressure mat data indicated a peak pressure on inhalation. When the horse was wearing the modified girth, the pressure spikes (speculated to be related to the intake of breath) were no longer evident.

It has been reported that the equine rib cage has a limited range of expansion directly where the girth sits. The shape and fit of the modified girth design reduces pressure from the intercostal muscles and therefore does not hinder the rib cage’s naturally occurring expansion.

The girth pressure studies in sport horses and racehorses suggest that muscle function could be highly significant in relation to the time it takes a galloping horse to fatigue. 

Muscles need to contract in order to work effectively. If pressure from the girth negatively affects muscle activity, this could result in restricted function and limit the limb’s full range of motion. Subsequently, the muscles may have to work harder and, if they are required to work harder, may fatigue faster. 

When scientific evidence shows that commonly used girths are compromising muscle function and restricting breathing during galloping, the advantage of the modified design becomes obvious.

Not so fantastic elastic

One anecdotal belief is that girths modified with elastic inserts offer some form of pressure relief, allowing the horse’s rib cage to expand, therefore enhancing instead of hindering breathing mechanics. However, in the sports horse research, adding an elastic component to the end of the girth did not result in increased locomotion or any alteration in pressure distribution beneath the girth. In contrast, the addition of the elastic decreased the stability of the saddle. Furthermore, new elastic girths can provide up to six inches of stretch and, as a result, are easy to over-tighten. With daily use, the elastic component of the girth weakens over time, losing its elastic properties and stretching. From a safety viewpoint, where elastic girths are being used in race training, routine checks of the stitching and elastic strength are crucial. 

Anticipated pain and ulcers

In practice, without the use of sophisticated measuring systems and in the absence of skin ulcers, girth pressures will largely go undetected. However, behaviour when being tacked up, particularly when the girth is being done up, can be indicative of girth-related pain and discomfort. 

Similar to humans anticipating pain, horses increase cortisol and gastric acid production, leading to gastric irritation. For horses that already have clinical signs of ulcers, this, combined with excessively high girth pressures in excess of 106kPa behind the elbow at gallop, is likely to lead to increased discomfort. As a result, health and performance are likely to be compromised.

The use of a pressure-relieving girth may be an effective tool when used as part of a multidisciplinary approach in supporting horses undergoing treatment and management of ulcers. If pressure-related discomfort is eliminated, it seems likely that the anticipation of, and response to, pain will be reduced over time. 

The area of peak pressure (shown in red) caused by a straight girth is avoided by the cutaway shape of the modified girth.

The research performed on the treadmill demonstrated that a straight girth created areas of high pressures in excess of 106 kPa behind the elbow, on muscles that are vital for locomotion and respiration. …

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