Equine Mechanics

Author: Sian Townson

  • Homework: lengthening without tension

    For Sue and Claire, who don’t get off that lightly!

    Stride counting exercise to be done at walk, trot, canter and leg yield.

    Choose two markers, tufts of grass or trotting poles and count the strides the horse takes between them. Concentrate on riding between them sitting tall and moving with the horse in a relaxed, swinging way. The horse should feel like they are dancing with you, not having a fight. Repeat, changing ONLY the number of strides the horse takes between the markers/poles. Some change of carriage (longer/shorter horse) is fine.

    DO: Prioritise keeping the same tempo, and the same relaxed, swinging rhythm, even if that means that it takes several attempts before you achieve a longer or shorter stride length.

    DO NOT: Cover the ground in half/twice the number of strides, but in a rushed or tense way.

    THE POINT: By concentrating on counting e.g. less strides between the markers you won’t be as likely to tense up or “force it” and should get a bigger, more ground covering movement in a more correct, obedient and elastic way. Counting also tests whether you are actually lengthening and shortening without the need for eyes on the ground.

  • Pushing off the ground – Newton and take off

    When a horse pushes off the ground to take off or just to travel, they have to obey the laws of physics:

    In order to take off:

    1, There must be a force (push)

    (Newton’s First Law – change requires a force)

    2,  The force must be enough to accelerate the horse’s mass. Think about trying to throw the horse up there yourself: it’s the change in speed and the mass of the horse that matter. 

    (Newton’s Second Law, Force=mass x acceleration)

    3, The floor must resist the push, or the horse will just sink. 

    (Newton’s Third Law, equal and opposite actions)

     In our picture our rider is ahead of the horse, and lifting with his hands.

    As he’s ahead of the horse his centre of mass is in front of the horse’s centre of mass. This prevents the horse from raising its front end effectively (and puts him at risk of a fall). Likely outcome: pole down in front.

    However he’s trying to compensate by lifting with his hands. This shortens the horse’s neck, bringing the head in. As the head and neck are a major part of the horse’s weight, this shifts the centre of mass backwards (caudally). This could help avoid the pole in take-off BUT also has implications for the rest of the jump. The head and neck act as a counterbalance over the fence, rotating the back end up. The longer the lever of the neck the more turning effect will apply to the horse (Moment =force x distance) so the higher the back end will go. A shortened neck prevents this adn lowers the back end. Likely outcome: pole down behind.

    So which was it in the case of this rider? I’ll leave you to decide.

  • Why Study Horses?

    As cursorial (adapted for running) locomotion goes, bottom of the food chain is really the lizards. They’re ahead of the snake, they’ve got limbs and even elbows to lift themselves off the ground, further increasing efficiency. However their shoulder design is a little primitive and they resort to side-to-side (medio-lateral) wiggling to move forward, wasting a lot of energy in the process.

    At the other end of the scale is the cheetah. The wiggle has gone and the spine dorsi-flexes (up-down) like a caterpillar. This increases stride length and hence speed by so much that the cheetah could do six mph even if it didn’t use its legs (Hildebrand, 1959). The cheetah is a sprinter, fast over short distances.

    The horse however, is not just adapted for speed but efficiency.

    – It has a fairly rigid spine, handy if you want to carry a rider.

    The stride length is increased by running on the toenails (unguligrade), with the heels (hock) and wrist (knee halfway up the leg), lengthening the legs. 

    – Extra bones have been lost, leaving just the middle toe, and all the muscles are at the proximal (top) end of the leg, with long tendons running down the limb. This makes the distal (bottom) ends light, increasing stride frequency.

    – Elastic energy is stored and released by the tendons, via the “extra” shock-absorbing joints that the horse has gained by running on its toes, particularly the fetlock, with the small proximal muscles acting as dampers (Wilson et al., 2001, Lawson et al., 2007). This makes the horse efficient.

    – Joint constraints keep the limb motion parasagittal. Stable and efficient.

     – The horse has no clavicle (collar bone). The scapula (shoulder blade) is held on by a musclar sling and hence can slide along the thorax increasing stride length and efficiency (Lawson and Marlin, in press).

    In fact the horse is an engineering marvel. If you want to understand the musculo-skeletal system, study the horse.

Equine Mechanics

Insights and resources on equine biomechanics for horse owners, trainers, and enthusiasts.