Your Horse From the Ground Up - The Hindquarters
 By mosquito   •   21st Oct 2012   •   23,113 views   •   3 comments
Your Horse From the Ground Up – The HindquartersWe’ve seen how the lower legs and hoof all work together to help the horse move, even without any muscles there. Now let’s start looking at how the muscles of the horse really give him power, speed, and balance. Where better to start than the actual ‘engine’ of the horse, the hindquarters?

The horse gets almost all of the power and energy for movement form the hindquarters. There is a simple but powerful structure of levers (the bones), controlled by ligaments, and powered by large, dense muscles. These muscles are where everything begins with the horse. Fortunately they are fairly robust, and injuries to the hindquarters – even the bones and soft tissue structures – are relatively rare. However, you still need to understand how they operate if you are going to take care of them – and get the best performance from your horse.

First, let’s look at the framework for these muscles, the bones of the hindquarters. There’s one thing you really need to know here – unlike the front legs, the bones of the hind legs attach directly to the spine – that makes them much more influential in the horse’s balance, and for things like getting your horse ‘into an outline’ or ‘on the bit’. What happens in the neck starts in the back, and what happens in the back starts in the hind legs. Forget about draw reins and bits for a minute, and let’s see if we can help you understand how to use the back end of the horse to get results in the front end!

The spine joins the hind bones at the pelvis. The pelvic bones are short and strong, and the ‘shoulder’ of the pelvic bones is what forms the point of the hip, and the other end forms the point of the buttock. Those pointy parts are out there for a reason; they need to be able to move in many directions and so have to be free of the restrictions of other bones and thick muscles. They move back and forth as the hind leg moves, and they also move up and down a bit to absorb impact. Notice how the hind leg has many more angles in the joints than the front leg? That’s important – with no ‘straight’ joints like the knee, the hind legs can absorb impact better – which protects the spine from impact through the pelvic bone connection.

The pelvic bone is actually six different bones when the horse is born, allowing the horse to grow and protect the spine form damage. Once the horse is fully grown, these six bones have fused into one solid bone. Be aware of that if you start backing your horses before they finish developing – especially if you are asking for work like racing or jumping before the bones have set. Limiting the weight carried and the requests for explosive power or very athletic collected work in youngsters is important to allow those bones to develop – and once they’ve set they’ll be much more powerful and effective too. The pelvis is the first of the ‘levers’ of the hindquarters to provide strength, speed and power. Like all levers, the longer it is the more powerful it is – a long pelvic bone means a powerful horse!

The femur, which roughly compares to our own thigh bone and is the longest bone of the horse, connects to the pelvis bone near the point of the hip, slopes forward and downward, and joins the patella, or stifle. This means the stifle is actually the horse’s knee, if we are comparing horse’s anatomy to our own! The femur is a strong bone, deep in the protection of the muscles, and is rarely injured, although the patella is another matter. The patella, or stifle, is very exposed, and is a common site of injuries if horses fall or get cast. Minor injuries from lying down on rocky or hard surfaces are also common. It’s hard to protect the area, but be aware of it and try to make sure your horse has cushioned surfaces to lie down on, and plenty of room to move around in a stall or box. Stifle fractures occur most often in jumping horses, especially eventers, from impact with rigid cross country fences. ‘Greasing’ your horse’s stifle, and of course responsible riding, are the best ways to prevent a stifle injury, as is making sure your horse doesn’t get bumped or banged by stable doors or gates.

Your Horse From the Ground Up – The Hindquarters

However, if you suspect your horse may have hit a fence hard or had a fall, keep an eye out for heat, swelling and pain at the stifle. Stifle injuries are very difficult to treat, and uncomfortable for the horse, but minor bruising and small fractures respond well to treatment, and the area is easily accessible for surgery if needed. Here’s another neat fact about the stifle – this is the part of the hindquarter bones that the horse can ‘lock’ to be able to sleep standing up. Once the horse locks the bones joining at the stifle, he can stay upright without much muscle effort. Some horse breeds, such as Morgans, commonly experience a ‘locking patella’, where the joint gets stuck and the horse has difficulty unlocking it. I had an Irish Thoroughbred with this problem. It was easily resolved by allowing her more movement – we never stabled her – and if she had room to move the problem never appeared. If your horse has locking patella, and pasture living isn’t possible or doesn’t work, it’s a fairly simple operation to permanently release the joint – but after that, remember your horse won’t be able to sleep standing up anymore!

The femur, at the patella, joins the tibia and fibula which slope down and back to the hock. These two bones are almost – but not always – fused together to make them stronger. They act more as a lever and less as an engine, and the muscle that powers it (the gaskin) is comparatively small. This muscle works mainly to help stabilize the joints of the hind leg – if your horse as conformational defects of movement (such as brushing or swinging the hind legs), strengthening the gaskin may help to straighten the movement of the hind legs. The tibia and fibula are short, strong, and not particularly exposed and seldom cause problems for the horse. They end at the tarsus – or hock – and that’s another matter.

Like the patella, the tarsus is very exposed, forming a boney protrusion sticking out behind the horse with no muscle protection and just waiting to get hurt. Hock injuries from falls, small stables, becoming cast, losing balance in a lorry or trailer, or kicking are all too common. The hock roughly compares to our ankle, and like our ankle is critical for the movement and stability of the bones below it. The hock is an anchor for the complex network of tendons and ligaments, controlled by the muscles above, and injuries to the collection of bones that make up the tarsus can have complications beyond the bones themselves. Swelling from a knock or bruise can put pressure on a tendon or ligament, or push it out of position enough to create injuries lower down the leg. In fact, many lower leg soft tissue injuries actually have their origins in the hock!

It’s easy to forget about the hock, but if there’s one part of your horse’s back end you take care to protect, make it the hock. Hock boots or tall shipping boots that cover the tarsus are wise for travelling, and if your horse is very large or a kicker then padding the stable walls with rubber maps is a good idea. At the first sign of heat, swelling or tenderness in the hock consult a vet – early intervention here may prevent a much more complex – and serious – problem later!

So those are the bones – now let’s take a look at those muscles! There are actually a pretty complex collection of muscles and sub-muscles, but it boils down to four main groups, so we’ll keep it simple.

The biggest, and most powerful muscles, make up your horse’s gluteus which is the big muscle that makes his rump. This muscle sits above the femur, and is your horse’s main engine. It compresses and expands to power the downward thrust of the hind leg as the horse pushes off, either from one leg at a time or from both legs simultaneously. It’s what helps the horse move, jump, and rear. It’s a large, dense muscle that is well fed by the horse’s system of arteries, and it rarely causes problems. What can – and often does – happen is that the gluteal muscles on one side of the horse will either develop or atrophy at a different rate than the ones on the other side. This isn’t usually a problem with the muscle itself however. This can indicate a problem with the bones underneath, such a pelvic bone displacement after a fall, or the horse moving differently due to an injury further down the leg. Uneven training – such as always working in the same direction, or if a horse becomes ‘one sided’, can also lead to different gluteal muscle appearance. If you stand behind your horse and notice that he seems ‘taller’ on more developed on one side, you might want to take a look at the weaker side for any injuries – bearing in mind they could be hiding much further down the leg.

Below the gluteals is the vasus, roughly the same as your quadriceps. This runs from the lower end of the pelvic bone down to end over the patella, making up your horse’s flank. Its main job is to help lift the hind leg forward, making it very important for dressage horse and other horses that need a lot of hind leg elevation or do a lot of collected work.

Down the back of the rump runs the semitendinosus, which is used to extend the hind leg out behind the horse, mostly for galloping. That’s why this muscle can be very developed in racehorses and eventers. It also is thick, large and strong, and rarely causes any problems.

The muscles of the gaskin are a set of parallel muscles running from the patella to the hock. The horse has muscles here on both the inside and outside of the leg, although the ones on the outside are the strongest and most conspicuous. These muscles help stabilize the hock joint.

Most of the soft tissue structures of the hindquarters are thick, strong, and well protected my muscles, and injuries are uncommon. The one you are most likely to notice is the horse’s Achilles tendon, which runs along the top and back of the gaskin, ending at the hock. Like your Achilles tendon, it is strong but exposed. Fortunately, despite being so visible, the tendon in horse is very durable, and is rarely strained or injured. To be honest, to do real damage to it (outside of an impact injury or a laceration from outside the horse), the bones and muscles are short and stable enough to protect this tendon from strain.

So that’s your horse’s hindquarters – remember if you want a powerful athletic horse, then don’t just look at the muscles. Look for that long pelvic bone, plenty of angle in the hip and patella, and a horse that looks straight and stable form the stifle to the hock. If those bony structures give you a good conformational framework, then you can build up the muscles to get yourself an athletic animal, even if what you are looking at today is young, fat, or out of shape! Next time we’ll look at how the hindquarters connect to the back, and the secret tricks to get your horse really balanced and on the bit, and get that perfect outline!
Terrific article, that was really interesting, can't wait for those secret tips for balance.
  Oct 21, 2012  •  25,130 views
PonyBox  MOD online
As always, extremely informative!
  Oct 22, 2012  •  25,184 views
PonyBox  MOD online
I always learn something new reading your articles. Thank You!
  Oct 29, 2012  •  25,166 views
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