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Biomechanics: from surface to spine

by
01 November 2014, at 12:00am

Marion McCullagh presents her first report from the 2014 congress of the British Equine Veterinary Association with a review of the sessions on arena surfaces and approaches to back problems.

THE British Equine Veterinary Association held its 53rd annual congress at the International Convention Centre in Birmingham from 10th to 13th September with a typically large attendance from both the UK and many overseas countries.

Very suitably for the international membership, Thursday morning started with a session on “World class performance: science and practice behind the medals”, chaired by Pat Harris of MARS HorseCare.

Lars Roepstorff of the University of Agricultural Sciences, Uppsala, Sweden, described his work on “Improving arena surfaces for performance and injury reduction”.

It had become apparent, he said, that there was a need to evaluate the effect of the surface on the welfare and orthopaedic health of the horse both in competition and in training, so a research project was started in 2007, backed by FEI, World Horse Welfare and the Swedish Foundation for Equine Research.

There is a balance between minimising injury while maximising performance, as better performance means more load on the musculoskeletal system. The surface plays an active role and maintenance of the surface is as important as its original design. 

Surface science

It is important to train the horse on a surface similar to the competition surface so that it can adapt and fine tune its movement at reduced work intensity before it is expected to compete at the peak of its ability.

Lars adapted the “mechanical hoof” that had originated with Professor Michael Peterson in the USA and set about working out how the physical properties of the surface interacted with the biomechanics, neurophysiology and orthopaedic pathology of the horse. 

He correlated this with riders’ comments and the performance of the horses. He has analysed over 400 surfaces and decided on five objective criteria of the surface: firmness, cushioning, responsiveness, grip and uniformity.

His second paper, “An overview of the biomechanics of surfaces, and the interaction of horse and surface”, was given in the “Whole horse biomechanics” session chaired by Thomas Witte of the Royal Veterinary College. In this paper Lars examined hoof-ground interaction in detail.

For the horse there are three distinct events: impact, support and push-off. The surface needs to be both yielding, to absorb the energy of impact, and resilient, to support turns and take-off. 

As the hoof hits the ground it decelerates, creating a force of 20 to 30 G on a soft arena, about 250 G on a trotting track and 1,000 G on tarmac. An aircraft pilot will faint at 10 G; this gives some idea of the force involved.

Sixty-five per cent of this force is absorbed between the hoof capsule and the cofin bone; impact has its greatest effect on the hoof but in trotters with extreme grip the carpus can be affected.

Too much force for too long leads to injury. In impact, the hoof brakes or slides to a stop and this is followed by the support phase where there is full ground contact and load.

Depending on speed, this may mean that the hoof carries up to twice the horse’s weight. This is the phase of maximum load; elasticity of the surface distributes the force and returns energy to the horse. Many surfaces show room for improvement in this property.

In the next phase of roll-over or take-off, the hoof lifts from the ground, the heel is lifted rst and then the hoof rolls over the toe.

From the point of view of the surface “impact firmness” is the hardness of the very top surface: how stiff it is on the primary impact. “Cushioning” relates to the whole depth of the surface: how much does it yield and how much does it support the horse? 

“Responsiveness” is a measure of how active the surface feels to the rider. A good surface feels springy. This depends on the natural frequency of the surface and how the material moves in response to the horse’s movement, influencing the energy that the surface gives back to the horse. It is related to stiffness and cushioning.

“Grip” measures how much the hoof slips during take-off, landing and turning. It relates to the movement in the material of the surface as well as to the movement between hoof and surface. “Uniformity” measures how the whole arena rides. Is there consistency throughout or are there uneven patches? Consistency over time is another vital component. The use of the surface, the weather, the initial construction and the method of maintenance must be considered in all their complexity.

Epidemiological studies have established how these parameters can predict risk of injury.

Thanks to Lars’ research, the functional properties of the surface have been quantified and objectively assessed but the final outcome depends on how the surfaces are used and how the horses have been trained to compete on them.*

Physiotherapy

Thilo Pfau, of the Royal Veterinary College, chaired Monday afternoon’s session on “Veterinary-physiotherapy interface”. Sue Dyson of the Animal Health Trust described “The veterinary approach to back problems”.

When a horse is suspected of having back pain it needs thorough clinical examination, both at rest and at exercise, as the source of pain may be in hind limbs or forelimbs rather than in the spine. Impinging spinal processes (ISPs) may show on radiographs or scintigraphy but they may not be the source of pain.

The horse needs to be examined during a full range of movement both on the day of arrival at the hospital and the day after; it needs to be seen in hand, on the lunge, with its own tack and rider and again with a skilled rider.

Back stiffness may be protective, a response to limb pain rather than being intrinsic. Unbalanced riding and poor saddle t can be big factors in the development of low-grade lameness and poor movement.

Few professionally produced sports horses are presented with back pain due to ISP problems. The good core muscle strength which follows systematic training and by being ridden in a round outline by a balanced rider means that the back is rarely over- extended; this may be protective.

The source of the pain is best located by diagnostic analgesia. Conservative treatment and retraining can often bypass the need for surgery but even where surgery is performed a rehabilitation programme is necessary to re-establish core muscle function.

A balanced rider, a well-fitting saddle and a correct pattern of work complete the picture. 

  • More details on surfaces are in “Equine Surfaces White Paper” which can be downloaded from www.fei.org/fei/about-fei/publications/fei-books.