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The Beauty of the Booty

Writer's picture: Genevieve KirkGenevieve Kirk

Increased strength of hindquarters is something we all want for our horses, (and ourselves!) This desire is both aesthetically desirable: we want to look strong; and functionally desirable: we want to be strong. It makes our jobs easier and more effective. These muscles are needed to hold our posture and aid movement in an energy-efficient way, and they need to be strong to do so. (1)


Strong hindquarters provide the push power, the sitting power, and the forwards engine that every discipline on horseback requires. Welcome to a short and sweet introduction to the anatomy and physiology of hindquarters, specifically the pelvic region.


Major bones of the hindquarters:

1.     Sacrum – A T-shaped series of fused sacral vertebrae which extend out of the lumber vertebrae.

2.     Pelvis – a very large symmetrical shaped bone that spans the width of your horse from hip point to hip point, and then to the point of buttock on each side of the body. (Is it just me or does it kind of look like a Gothic Calligraphy designed V when seen from above??? See the following picture.)

3.     Femur & bones of the limbs – not the main focus of this article, but big, thick and solid bones to withstand contraction forces of the muscles and ligaments attached to them.

 



Major muscles of the Hindquarters:

Horses have 3 Gluteal muscles (2):

1.     Superficial Gluteal or Gluteus superficialis: a relatively thin and small layer covering the middle gluteal.

2.     Middle gluteal or Gluteus medius: the largest muscle of the equine body, and the main hip extensor.

3.     Deep Gluteal or Gluteus maximus is found deep to the middle gluteal, and aids function of hip extension.

 


These muscles originate from gluteal fascia found at your horse’s equivalent “lower back” aka lumbar back (3) and the Ilium, which is the stretch of bone found between the middle of the pelvis and the “point of hip” which is the landmark of bone labelled “Tuber coxae” (see image above). They insert on to the greater trochanter of the femur (which is the bony projection next to the hip joint), and on to parts of the sacrum. This location means that when the gluteal muscles contract, the femur is pulled backwards (and slightly abducted) from the body, thereby causing extension of the hip. (4)

 

In addition to the Glutes, The Hamstrings are crucial in the power factory that is the hindlimbs. These are made up of:

1.     Semitendinosus

2.     Semimembranosus

3.     Biceps femoris

4.     Gracillis

 

Overall, these aid hip extension function, with the addition of stifle flexion.

 


 

Left hind = hip and stifle flexors engaged. Right hind = hip and stifle extensors engaged.
Left hind = hip and stifle flexors engaged. Right hind = hip and stifle extensors engaged.

In this picture, Horacio's right hind hip extensors are the only thing carrying his weight. The strength and power those Glutes (and other muscles) have to demonstrate in this moment of EVERY stride is why they need to be well-conditioned, strong, and well-recovered. It also hopefully shows that without those extensors, we would remain in a squat position indefinitely. This means there is no weight carrying capacity without the Glutes and hip extensors.


To put in to the context of one form of injury risk; Horacio's right hind also demonstrates major fetlock extension; his fetlock is at a near 90 degree angle. This range of motion is being supported by the precious tendons and ligaments of the lower limb. If the muscle conditioning of the body has not been thorough enough, and the horse's body is being over-strained for what it is prepared for, these tendons risk injury. Weak muscles become unable to hold the weight/posture asked of the horse, and the tendons become stretched beyond their potential.


How or where that excess strain reveals itself depends on a million factors; one that if we had the answer to we would never have an injury again. The general consensus we should all be realising though, is that poorly conditioned hindlimbs and bodies mean parts of the body are then over-strained, which we should all be trying to avoid.







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