When a horse moves, its limbs perform a cyclical movement in two phases: the stance phase (damping – bearing – propulsion) & the swing phase (bringing back – suspension – embracing). Several factors can influence and modify the stride, such as the anatomical conformation (breed, hoofs, morphology) or the nature of the surface (hard or soft).
Today, the vast majority of horses are more comfortable on a soft surface which improves propulsion, and shock absorption, and makes their locomotion lighter. But how does the ground affect the horse’s movements? Is it possible to quantify these variations in locomotion?
Surface type and characteristics
In order to analyse the impact of the surface on the horse’s locomotion, it is essential to understand how it is composed. Tracks and arenas are made up of a surface layer called the work layer, which offers freedom of movement to the horse’s feet due to its flexibility. This is followed by a firmer foundation layer that provides support and drainage for the work layer.
The research programme called « Sequisol » (Safety – Equine – Surface), carried out with a complete experimental protocol combining dynamometric, accelerometric and kinematic measurements, has made it possible to characterise the effects of equestrian surfaces on the locomotor system and the locomotion of racehorses and sports horses, under real training conditions. The first results for canters confirm the shock-absorbing nature of the fibre-oiled sand tracks. On this type of track, the anatomical formations (bones, tendons, joints) of the distal part of the forelimb are less stressed than on a traditional grass track, especially during the damping phase. This effect is primarily caused by increased ground deformation.
Biomechanical effect of surface type on equine locomotion
In general, whether the horse is sound or lame, the ground has an effect on its locomotion. It is therefore essential to first understand how it influences the movement of a sound horse.
1. Biomechanical effects of the working surface
During the stance phase, the biomechanical effects of the surfaces on the horse’s locomotor system evolve. The movement is divided into six phases (Denoix and al. 2016): impact, which follows landing, braking, intermediate joint extension, maximum vertical weight-bearing, and finally propulsion and heel extension, which precedes the lift.
The shock of the impact is mainly due to the surface preparation, hence the importance of harrowing a track as this considerably reduces the impact force. This shock, which can be strong or weak, allows you to judge the track’s “superficial” firmness. Indeed, whatever the track, sand, or dirt, the impact shock is divided by 2 to 3 after harrowing.
When comparing three work layer thicknesses at the canter, the shock impact increases over a layer thickness range of 7cm to 13cm. When three work layer thicknesses are compared, the shock impact does not decrease significantly over layer thicknesses ranging from 13cm to 20cm. As a result, the thickness of the work layer has no effect when it is less than 13cm. Furthermore, tracks with varying “depth” firmness can produce similar impact shock results.
At the trot, the deceleration at the hoof on the road is 23 times greater than on a sandy track, and the vibrations perceived at the foot have a frequency of about 600 Hz on the road versus 41 Hz on the track.
2. Hard surface / soft surface: which effects?
Horses have tendons and joints that are extremely sensitive. Some horses, such as those with sensitive tendons, will feel more at ease on hard surfaces because they facilitate their locomotion. Other horses, such as those with joint problems, will move more smoothly on soft surfaces.
Nowadays, thanks to locomotion quantification tools, it is possible to objectively evaluate the changes in locomotion induced by the nature of the surface. The visual below shows the comparison of the asymmetry indices of Arion – a horse that regularly competes in show jumping and is considered to be sound – in straight line, hard surface / soft surface.
Interpretation of Arion EQUISYM results:
– For the withers, the amplitude of elevation remains identical on soft and hard surfaces, with a very slight asymmetry defect in the left forelimb (-2%).
– For the pelvis, Arion’s locomotion deteriorated slightly on soft surfaces with an increase in the asymmetry of the right hindlimb from 5% to 7%.
– Overall, Arion has a slight locomotor asymmetry defect in the left fore – right hindlimb, more marked in the right hindlimb. The surface type did not significantly affect Arion’s locomotion.
In this picture, straight-line locomotion on hard surfaces is represented by the green curves and indices
and straight-line locomotion on soft surfaces is represented by the blue ones.
For light horses with good balance, the surface condition has little importance. However, other factors are relevant: the level of the rider and the fit of the saddle, but also the trimming, shoeing and eventual osteo-articular problems..
Impact of surface type on locomotor lesions
When the foot bears down, asymmetry generally increases. Visually, the horse raises its neck when putting its weight on the pathological limb, and lowers it when supporting the non-lame limb. The right-hand circle will tend to increase the asymmetry of a horse with a right forelimb lesion.
As discussed earlier, overworking or working on unsuitable surfaces are the most common causes of lameness. Hard surfaces increase the risk of premature damage to distal joints, which can lead to joint disorders (up to the knees and hocks) and foot disorders. On this type of surface, the work sometimes tends to tire the joints. However, the exercise of the circle on a hard surface reveals the osteoarticular lameness caused by intense and/or repeated efforts at the level of the articulations.
Floors that are too deep, on the other hand, place more demands on the tendons, returning less energy to the limbs upon impact. As a result, the musculotendinous system is put under more tension. Repeated exercises on this type of floor can lead to tendon or ligament disorders (tendonitis or sprains).
In conclusion, if a floor that is too hard puts excessive pressure on the joints, a floor that is too deep will have a negative effect on the tendons.
Conclusion
Surface analysis is an important part of preventing equine lameness. It has been demonstrated in humans that there is a link between the development of chronic musculoskeletal injuries and repeated shock exposure.
The ideal surface, suitable for all situations and all types of horses, does not exist. Each type of surface, because of the way they are made or maintained, will better suit a specific discipline or need, such as the rehabilitation of musculoskeletal conditions. It is still important to work a horse on a variety of surfaces in order to get the maximum benefit from each.
SOURCES :
Crevier-Denoix, N., Chateau, H., Munoz-Nates, F., Ravary-Plumioen, B., Camus, M., Falala, S., Denoix, J.-M. and Pourcelot, P. (n.d.). [online] Available at: https://www.vet-alfort.fr/images/enva/recherche/unites-de-recherche/BPLC/r1959_9_equidee-article1-decembre16.pdf [Accessed 21 Nov. 2022].
Ifce.fr. (2022). [online] Available at: https://equipedia.ifce.fr/sante-et-bien-etre-animal/maladies/appareil-locomoteur/effet-biomecanique-des-sols [Accessed 21 Nov. 2022].je
Keywords: surface impact, locomotor injury, equine locomotion, equine physiology, EnvA, CIRALE