FEI Footing Report–Highlights

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The 2012 Olympic competition arena. Wax coated sand was installed for the test event a year before the Games but after complaints from dressage and jumper riders was replaced with footing of sand, felt and fiber. © Ken Braddick/dressage-news.com
The 2012 Olympic competition arena. Wax coated sand was installed for the test event a year before the Games but after complaints from dressage and jumper riders was replaced with footing of sand, felt and fiber. © Ken Braddick/dressage-news.com

An Equine Surfaces White Paper prepared over four years by eight experts from six universities in Great Britain, Sweden and the United States has been published by the International Equestrian Federation (FEI). The report does not draw conclusions or make recommendations but compiled the latest data on arena and turf surfaces, and the effects on horses in training and competition.

Key properties of footing, and the effects on horses’ physiological and biomechanical responses, are described in the white paper, as well as the optimal composition, construction and maintenance of arenas for maximizing equine performance while minimizing injury risk.

The Surfaces White Paper is the biggest international collaboration of its kind and was funded by the FEI, World Horse Welfare, the Swedish Foundation for Equine Research and the British Equestrian Federation. Dr. Sarah Jane Hobbs, research lead in equine biomechanics at the University of Central Lancashire in England and member of Research and Consultancy in Equine Surfaces was the lead in preparing the document.

Some highlights:

The volume of exercise in competition is another important consideration, as the intensity is likely to be greater than during training. In addition, the surface at a competition may be quite different to the training surfaces used at home. A horse should be expected to work on a variety of surfaces during training in order to condition the musculoskeletal tissues so that they are fit to perform higher intensity exercise on a competition surface. Understandably riders expect the surfaces at competition venues to be good quality, but there are currently no guidelines or grading systems. In addition, there are often disparities between the functional properties and characteristics of warm up and competition arenas even though it is considered beneficial for the warm-up arena to be the same as, or at least similar to, the arena the horse will compete on. A grading system for arenas would allow riders and trainers to select appropriate competitions with greater consideration for a horse’s fitness and performance history, particularly as there is a higher risk of injury with higher intensity of exercise.

Dressage movements involve high levels of collection (passage and piaffe), extension (extended trot and canter) lateral movements (travers, renvers, half pass) and rotational movements (pirouettes). The properties of the arena surface are expected to be important to the successful execution of each movement, but to date only some measurements of elite horse-rider combinations are available.

Collected movements
Collected movements require a reduction in forward motion without an alteration in cadence, elasticity or impulsion, which demands a greater reliance on static rather than dynamic equilibrium. Modifications in foot placement patterns, which enhance center of mass (COM) stability include prolonging stance durations, increasing overlap durations, and reducing or eliminating
suspension phases. Of the collected gaits, piaffe was found to have all of these modifications and therefore considered the closest to static equilibrium. Compared to trot, passage has a shorter airborne phase and higher flight arc, which is achieved by increasing the vertical impulse in fore and hindlimbs, but not the magnitude of peak force. There is also a shift in the load distribution to the hind limbs with greater positive dissociation between hind and forelimb foot strikes and an increased weight-bearing function. Greater flexion is seen in the hindlimb and lumbosacral joints, but this is not achieved by stepping further under the body with the hindlimb, as the hoof contacts the ground in a more caudal position. As a result.. storage of elastic strain energy in the hock and pelvis may be of great importance for passage. The performance of the surface to support applied loads without large energy losses, but at lower strain rates (due to the longer stance durations) is therefore essential for collected movements.

Extended movements
Little information is currently available on the extended movements of trot and canter, which require the horse to cover as much ground as possible, in a lengthened frame, without hurrying. Elite horses were found to execute the extended trot at an average speed of 4.93 m/s with a stride length of 3.55 m and stance durations of 273 and 276 ms in fore and hindlimbsrespectively. It was also suggested that for top marks a speed of 5.4 m/s and stride length of 4 m would be expected. This compares to working trot at 3.61 m/s with a stride length of 2.73 m and increased stance phase durations of 341 and 339 ms in the fore and hind limbs. Extended canter speeds were reported to be in excess of 7.1 m/s to achieve the highest scores at the Olympic Games in 1988 with increases in stride length, but not stride duration. The increase in speed and demand for a long stride combined with a decreased stance time suggest that larger peak forces must be developed but also that greater impact shock will be experienced by the limbs. Currently, the data most comparable with extended trot of dressage horses come from racing trotters performing on different sand preparations and moisture contents at comparable or faster speeds. Although impact shock characteristics were increased on the firmer, wetter surface (which may be considered as detrimental), the yielding drier surface was unable to support peak loads. So, to maintain the same speeds on the deep, dry surface the horses produced equivalent impulses by increasing limb stance times. This was achieved by reducing stride length and increasing stride frequency, which is undesirable in dressage. So for extended trot, the surface is required to support higher applied loads at higher strain rates with higher shear strength during propulsion, but with lower deceleration and vibration frequencies at impact.

Rotational movements
The canter pirouette is performed in collected canter with the forehand moving around the haunches in a circle with a radius equal to the horse’s length. A 360 degree pirouette should be completed in 6-8 strides, and should maintain the activity and clarity of the canter. To turn, the limbs on the outside of the circle need to push in the opposite direction to the horse’s motion to rotate the COM around the leading hindlimb. In elite horses duration of the pirouette strides were reported to be significantly longer than collected canter strides, and there was no suspension phase, so there was overlap between leading forelimb lift off and trailing hindlimb footstrike. As the leading hindlimb is grounded for approximately 50% of the stride (540 ms stance duration for a stride duration of 879 ms, and each stride covers 45 to 60 degrees of rotation, this limb may be subjected to a notable amount of torque if the surface does not allow any rotational shearing. The canter pirouette, like piaffe, is
closer to static equilibrium conditions, so the surface must perform under lower strain rates, supporting an almost static load whilst allowing rotational shear for the leading hindlimb, but also resisting horizontal shear sufficiently as to allow rotation to be produced during propulsion of the other limbs.

Lateral movements
In shoulder-in, half pass, renvers, and travers the horse is evenly bent in his neck and body, but moves on more than two tracks. To move laterally the horse must push sideways, producing larger transverse forces at the ground than those produced in a straight line (Clayton. These movements create an unusual strain on the horse’s back and an additional twisting movement on the appendicular joints. Similar to rotational movement, the shear resistance of the surface is expected to be most important to the execution of the movements and reduction of injury.

It is generally believed that a surface with optimal performance is associated with a greater risk of injury whereas a surface that has shock absorbing properties will be detrimental to performance. The trade-off between high performance and low injury rate is not a given in human biomechanics where improved performance has been linked to much lower injury rates in at least one study. The absence of a link between injury and performance has not yet been shown to be true in equestrian events. In addition, the optimum surface for a specific sport is yet to be determined but has been described… as needing to minimize concussion through energy absorption, whilst still returning suitable power to aid performance. There is also a need to optimize shear strength, where optimization is likely dependent on the event. This is an area that requires further research. As the balance between safety and performance is highly dependent upon the functional properties and characteristics of the surface, it is important to understand the characteristics and performance of the individual parts of the system as well as having standard measures that can be taken in-situ.

In recent years there has been an increasing trend towards the use of artificial and synthetic surfaces rather than grass surfaces for training and competition arenas. Factors associated with this increase potentially include climate, greater demand for all year round use, ease of maintenance, planning considerations and taxes levied on buildings (particularly related to the construction of indoor arenas), greater rider awareness of performance and injury risks, the emergence of surfaces composed of silica sand and other materials, and an increase in the number of manufacturers and suppliers of these products. Nevertheless, grass arenas are still used worldwide where the climate is favorable and they are also used at elite level competitions on established sites.

There are many different types of artificial surfaces on the market for the various equestrian sports, which can be sold as individual components or mixed with additives according to the requirements of the buyer and the intended use of the arena. To date however, the manufacture and selection of materials have been based largely on empirical evidence and marketing factors. The surfaces used most commonly in training arenas by dressage riders in the UK are sand and rubber, sand, woodchip, and sand and polyvinylchloride (PVC). The additives can include synthetic or natural fibers of varying lengths, rubber, cloth or felt strips. A polymer or wax coating is applied to a number of the commercial surfaces; it serves as a binder between the particles and, depending on the coating material, can create a hydrophobic coating layer. The surface is then usually supported on an engineered foundation or drainage system. The geographical location of the arena may affect the ability to source certain materials and it may only be feasible to utilize surfaces that are locally available, which may influence quality control of the materials.

Grass based
Historically high level competitions on established sites used a turf surface, but the difficulty in maintenance and days lost due to bad weather alongside the development of synthetic surfaces has meant there has been a shift towards other solutions. Some venues have opted for all weather surfaces, which are usually based on sand and fiber mixes whilst others have invested in ‘all
weather’ turf, such as Hickstead in the UK that hosts the Hickstead Derby and the Royal International Horse Show. A ‘second generation gravel carpet’ that enhanced the drainage and base layer thus increasing the ability to manage consistency regardless of environmental conditions was installed at Hickstead. Grass based surfaces are suggested to provide the horse with what is often described as a more natural footing, but the functional properties will be highly dependent on the quality of the root structure and the moisture content. Poorer quality or overly wet turf surfaces can lack shear resistance and the use of shoe studs or caulks may be necessary. Conversely, compaction of grass based surfaces can occur over time which increases bulk density and hardness. The presence of organic matter has been found to strongly influence bulk density and consequently the ability of the soil to compact.

Rubber and Woodchip
Rubber and woodchip based surfaces are commonly used and are usually cheaper to buy than premium sand-based surfaces.= Two forms of rubber additives can be used in arena surfaces although alternative forms may also be found; 1) rubber crumb which consists of regular particles of 2-5 mm in diameter and 2) larger rubber pieces which are 25-40 mm in diameter. Rubber crumb is mixed into sand surfaces whereas rubber pieces are laid (to a depth of 50 mm) over rolled sand subsurface. The rubber source material is usually either new rubber, usually EPDM (Ethylene propylene diene monomer) or ‘alternative’ rubber such as shredded carpet backing and tubing, or processed tire or belting rubber. Processing removes the steel reinforcement belts and foreign objects from tire waste, leaving pieces of rubber and any associated fiber backing or reinforcement. Tire rubber is available in high volumes (at a low cost) and as such represents a preferential raw material for economic surface production. The rubber is effective in reducing compaction of either a sand or woodchip surface because rubber compresses with almost no change in volume and so opens up pores in the surfaces when pressure is applied. Injury risk may be increased on woodchip and rubber surfaces where routine maintenance is not carried out due to a lack of consistency. Woodchip used as a primary surface is also reported to increase the occurrence of slipping in horses. In contrast, a woodchip layer below the primary surface is reported to provide more cushioning by significantly reducing hardness and increasing shock absorbency. Degradation of these materials can affect the functional properties so the rate of degradation should be monitored and the surface should be refreshed when needed.

Sand with additives
Some arena manufacturers recommend using very fine angular or sub-angular silica sand with up to 15% clay or silt content (<63 μm diameter) to provide a firm surface of approximately 15cm in depth. In more traditional wax coated arenas sub-rounded sand with high quartz content is used to ensure durability of the sand and to maintain vertical drainage. The sand particles themselves have a high modulus of elasticity. The addition of polymer or natural fibers and rubber particles adds elastic recovery from impact and reduces compaction. If sand with a narrow particle size distribution is used, it is usually beneficial to add a binder such as wax to produce sufficient shear strength and some level of cohesion to avoid creating deep hoof prints and to provide lateral support when turning. The way the sand responds to any of the added materials depends on particle size distribution of the grains, which affects the bulk density, compaction, water retention and dustiness of a surface. The use of fibers in a sand based surface appears to have many advantages, as they are thought to create a root-like structure and are reported to increase the stability and drainage of games pitches. At higher confining pressures the mechanics of fiber reinforcement of sand is well established. However, high quality fibets that are dust-free are expensive. In the UK sand based surfaces appear to be most popular for dressage riders… at least 77% of British dressage riders responding to a survey had a sand based surface.

Wax coated sand and fiber surfaces are also offered on the equine market however, this is usually at a premium because the properties allow for long term performance under a variety of conditions. Paraffinic and microcrystalline wax is commonly used as a binding polymer. This material in the form of a relatively unrefined slack wax has cohesive properties and has a high oil content. The unrefined nature of the material requires blending to obtain the phase transition points and viscosity required. More recently there has been a lot of activity in coatings that are more selectively tailored to applications that can make use of a polymer combined with a solvent for coating of the particles. Permanent competition centers or arenas in high use often provide waxed surfaces, as better longevity with less maintenance has been reported. It could be considered that these surfaces are more uniform at a wide range of moisture content and are thus less sensitive to weather with the exception of large shifts in temperature. When compared to sand and woodchip surfaces, the incidence of lameness and injuries is reduced. This is supported by data from a waxed track, which showed a significant reduction in impact shock related variables during trotting compared to a crushed sand track.

Other surface materials
Other combinations of surface materials are used in different geographical locations according to cost, local availability of materials and environmental considerations. Often these surfaces incorporate cheaper natural or recycled materials, which include but are not limited to carpet strips, rubber from tires, plastic coatings from wire and dirt.