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Why Are The Biomechanics Important?

Assessment and observation before treatment.


Before I treat any horse or dog, I spend a lot of time listening to the owner, listening, observing and assessing the animal’s conformation, posture and movement. I do this because despite many horses or dogs having similar anatomy, their conformation and movement can be very different, refer to Image 1 and 2 below.





Image 1; TB yearlings at the sales in 2020. Top image- notice how well muscled the yearling is compared to the yearling below.


Conformation is the major difference between the two images (image 2 below) above, despite the horses being of similar age and breed. Body proportions, limb lengths, angles of joints all influence the forces generated by the connecting soft tissues to influence the movement and ultimately the performance of your animal. When looking at the conformation, it is important to look at the angles of the forelimbs and hindlimb to predict and understand their roles in supporting body weight and propulsion during movement.


Image 2 below. The angles of both yearlings are very different despite being the same breed and of similar age. Please be aware that the white dots are not accurate markers.


It is important to understand the limb angles and conformation of your horse or dog because this will give you a baseline understanding of how they will move . Animals that have a more upright limb angle, like an elephant, are more suited and built for stability providing support for their weight, however they would be limited to a slower speed compared to a horse or even a cheetah. Animals which have more angled limbs have greater length to straighten those limbs with the support of the extensor muscles and provide greater propulsion and speed, however their ability to carry weight is decreased.



Forelimbs versus the hindlimbs


When assessing the conformation, it is also important to look at the angle of the front leg compared to the hind leg and understand that they have very different functions. The foreleg is designed as a strut and actually slows down the speed of the animal compared to the hind leg which is designed for propulsion. In particular, if we focus on the stifle angle (image 2) which is angled forward towards the body, helps to push the body forward when the limb touches the ground. Compared to the elbow angle (image 2) which is positioned facing towards the hindquarters, helps stabilise and slow the animal down during movement.


Why is this important?


If we refer to image 3 below, we can see that the hind quarters in this young horse are higher than the front end, highlighted by the red line at the top of the back. This suggests that if this horse was to be worked hard their would be a greater chance of injury, due to the forces and propulsion of generated by the hindleg would be greater than the deceleration and stability of the forelegs.


Image 3; Yearling at the sales in 2020 showing croup high conformation.


Movement or locomotion is the result of when the feet/ hooves press against the ground to develop ground reaction forces. During locomotion, muscular contractions generate forces that move and stabilise the joints. As a result, conformation is not only about looking at joint angles and limb lengths but also understanding that different muscles have different fibre type (table 1 ) , length direction (image 4 &5 below) activation.


Muscle Function (fibre types)


Table 1: Summarises the different fibre types and their contraction speed and fatiguability.

Fibre type

Speed of contraction

Fatiguability

Type I

Slow

Low

Type IIa

Fast

Intermmediate

Type IIb

Very Fast

High


Image 4: Illustration of a prime mover muscle.

Image 5: illustration of a joint stabilising muscle


Assessing posture and overall muscle development allows me to identify which muscles the animal is using and which muscles are not being used during movement and stability. Prime moving muscles (image 4) are generally located across several joints and perform different functions depending on which part of the muscle is activated and also on how the antagonistic muscles are working. The main function of these muscles is to provide speed and power during locomotion. Examples of these prime moving muscles include the rectus abdominis and middle gluteals. The type of muscles I am drawn to during assessment and movement are the joint stabilising muscles (image 5) such as the transverse abdominis, multifidi and vastus medialis obliquus. These muscles are deeply located, close to the bones and joints and cross over one or more joints. The important difference between these muscles and the prime mover muscles are that they are highly anticipatory, meaning that they activate before the prime movers. This suggests and supports the idea of including a variety of training types and styles into your training targeted at stabilising and strengthening the joint stabilisers.


Image 6: illustration of the triceps muscles in the horse.


Another important point when thinking about the type of training we do with our animals is to understand the different muscular actions; concentric, eccentric and isometric. For example the tricep in the horse (image 6) is an important extensor for the elbow in the horse. During the swing phase the forelimb is protracting due to the extrinsic muscles of the forelimb (eg. Brachiocephalic) creating a concentric contraction. During retraction of the forelimb we tend to see an eccentric contraction occurring. Therefore the triceps, alongside other soft tissue (everything is connected remember) helps extend the elbow in late swing phase and also prevent the elbow from flexing during stance phase. From a practical perspective if we refer back to image 2 of the yearling from the sales, it is easy to identify how overdeveloped the triceps are in this young horse just from observation. Now that we know the anatomy and function of the Triceps in the horse we can start to apply this to other muscle chains around the body, and start to recognise that when a horse or dog is underdeveloped (lacking muscle) in one area of the body. Identifying, monitoring and speaking to skilled trainers or practitioners to understand why these muscles are underdeveloped will give you the doorway to creating exercises targeted to improve them. My advice before putting your horse or dog through an exercise plan targeted to improve their weaknesses is to understand why they are weak first. For example referring back to image 1 and 2 above it is obvious to see why the second yearling would have asymmetry through the muscles of the body due to the height of the hindquarters compared to the withers. In this circumstance one might want to ask yourself if exercises are the answer or rest and time to allow the yearling to grow and mature to a level skeleton.


Thank you for reading!


Any questions please do not hesitate to contact me : info@animalchiropractoruk.com









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