Before we delve into conformation and performance in the horse, let’s take a moment to differentiate conformation versus posture. What’s the difference? Conformation is form and structure of a body - generally we can’t change conformation. For example, I have short limbs and a long torso and neck. This, I cannot change. In contract, posture is dynamic and always changing. For example, I can sit in a slumped, flexed thoracic and lumbar spine posture as I sit and write this blog, or I can change my posture and sit up taller, with my pelvis in a more neutral position and my spine adopting a healthy S shaped curve.
Our last blog post discussed the link between confirmation of the dog and athletic performance, and this week we turn to the horse, Equus caballus. Just like the dog, horses formed a symbiotic relationship with humans and are intimately entwined in our history and the development of our civilisation. Humans, in turn, are largely accountable for the development of hundreds of breeds of the horse, each with their own unique conformational characteristics.
In his wonderful book The Nature of Horses: Their Evolution, Intelligence & Behaviour, Budiansky (1997) eloquently describes how Equus caballus came to be domesticated around 6,000 years ago. Since then, modern horse breeds have been largely shaped by human intention and need.
“It is scarcely possible to doubt that the long-continued selection of qualities serviceable to man has been the chief agent in the formation of the several breeds of the horse” - Charles Darwin
In the horse, conformation and breeds evolved according to the environment in which they inhabited and as a result of the needs of man. Like the dog, differences in conformation are seen between various breeds of horse. These variances evolve as a result of the demands placed upon the animal to perform.
A good example of how morphology (form and structure) and performance differ between two breeds is illustrated by the Quarter Horse and the Arab. Research by Crook and others in 2008 revealed that in comparison to the Arab, the Quarter Horse has larger hindlimb muscle mass, cross sectional area and volume as well as longer muscle belly lengths, all of which allow this breed of horse to generate high forces to accelerate quickly. In fact, the Quarter Horse was named after its ability to utilise it’s hindquarters to accelerate quickly and reach unrivaled speeds of up to 85 kph over short distances, about a quarter of a mile, even outperforming the Thoroughbred over this distance. When it comes to endurance however, the Arab outperforms all other breeds, maintaining a steady pace over distances of up to 100 miles.
The top speeds reached by the Thoroughbred are attributed to conformational factors similar to that of the Greyhound; long light limbs, less distal muscle mass, efficient elastic storage and return of energy, all allowing for a long, fast and efficient stride. Research by Komosa in 2013 revealed that the Thoroughbred is predisposed to perform well at speed with a medium length scapula and narrow light metacarpal bones which link the carpus (also known as the knee colloquially) and the metacarpophalangeal joint (fetlock). Conversely, the Polish Half-bred horse excels at show jumping due to the long section of the distal aspect of the hindlimb in relation to a smaller trunk length. It is these conformational differences which allow each breed to excel at different disciplines.
Utilising this knowledge, we can generalise that Thoroughbreds are likely to excel at jumps racing if they have a wide distance between each mandible, a large flexor shoulder angle and a large hip angle. Taller Thoroughbreds tend to be more successful racers, with a higher wither and hip height and a longer body allowing for a greater stride length.
Warmbloods are breeds often utilised in show jumping and dressage. A long sloping shoulder and large hock angle facilitate successful performance in these areas. The conformation which is typical of Iberian breeds allow for the gait characteristics considered desirable in the sport of dressage.
Just as conformation can allow an animal to excel in various performance criteria (ie. speed versus agility), conformation may be less than ideal and predispose the animal to musculoskeletal disease. Ideal conformation in any animal will be based on balance and symmetry. Faulty features can be static or dynamic in nature and may be due to an excessively narrow or wide base of support, or excessive angulation or rotation in a joint. There are many common faults that can be seen in the horse; for example a forelimb toe-in posture will predispose the horse to a winging-out gait pattern and potential interference with the hindlimb which increases the risk of a traumatic injury.
There is a growing body of research evaluating conformation of the lower leg and the hoof in performance of the horse. Poor hoof conformation and balance are commonly implicated in lameness. Research by Gordon and others in 2013 described the lower limb and hoof conformation seen in a population of Mongolian horses (a primitive type of horse) who did not receive routine hoof care and found that there were few conformational abnormalities; likely a result of the hoof interacting naturally with the ground.
A camped-under posture of the forelimb and more upright pastern can predispose the horse to tendinitis of the superficial digital flexor tendon and potentially navicular joint issues. Moving up the limb, musculoskeletal problems in the carpus can be caused by poor distal limb alignment. Research by Anderson and others in 2003 found that effusion in the carpus increases for every 10% increase in dorsal (the palmar hoof angle ratio). The authors also found that horses with a longer scapula length had a decreased risk of lower limb fracture. Furthermore, lateral deviations in the carpus and tarsus (hock) increase the risk of tendinitis and pelvic fractures in the racehorse, likely due to unbalanced forces in locomotion.
In summary, conformation can offer athletic prowess and contribute towards excellence in performance in specific pursuits, however poor conformation can increase the risk of traumatic and degenerative musculoskeletal conditions. It is worth bearing in mind that to date the assessment of conformation in animals has been more art than science, though more research is being done now to look at the link between genetics, conformation and injury risk or risk of particular neuromuscular diseases.
All of this is particularly important to physiotherapists who should consider the breed of the animal when developing a clinical picture, with a concise assessment of static and dynamic conformation forming the basis of the clinical reasoning process.