The last of our series of articles debunking common anatomical misconceptions looks at the trapezius muscle and the posture in the area just behind the scapula.
It’s common to see horses with hollows at the back of the shoulder blade, and you’ll often hear people say that it’s caused by atrophy of the trapezius muscle because of poor saddle fit. This is, in some part a correct assumption, but the bit that's not quite correct is the mention of atrophy of the trapezius muscle.
Trapezium Muscle Facts
The trapezius muscle is relatively small and the insertion point of the thoracic part of the trapezius muscle only attaches off the upper third of the scapular spine, as you can see in this drawing. It then comes diagonally back to the spinous processes in the wither region, meaning it doesn’t actually fully cover the area where you see the hollowing.
This muscle is relatively thin. On a pony, it will be about a centimetre thick, sometimes less, and in a horse it’s probably around two centimetres. Now consider the size of the hollows that you see behind the scapula, they can be 10 centimetres or more deep. This reveals that the hollows aren’t just caused by the trapezius muscle.
The other reason people assume it’s the trapezius muscle is that in a lot of anatomy books, the thoracic part of the trapezius is drawn quite a lot larger than it is in real life.
It's important that when we are studying the muscles of the horse that we look at an accurate representation of the thoracic part of the trapezius muscle.
What Causes the Hollows?
It's perfectly understandable that people assume that the hollow is caused by the trapezius muscle, but the reality is, there are a number of other possible causes.
1. Muscle Atrophy
The main muscle in that area is longissimus dorsi. If you have atrophy in that muscle it can cause a hollow behind the scapula. True atrophy of longissimus dorsi isn't just exclusive to that area. The hollow carries on throughout the back and if you look at the area in the neck, in front of the scapula, above C4 and C5, you will often see a hollow in that area as well. This is the first thing to check if you think the hollows might be caused by longissimus dorsi.
2. Conformation and Breed
The next thing we need to discover in the mystery of the hollows is, are they caused by muscle atrophy at all or is this hollow you see behind the scapula caused by something else?
To try and answer this question, it's interesting to consider different shapes of horses, varying conformation, and different breeds and types.
For example, horses with very high withers and more acute back angles – the type that would wear a narrow saddle - will often have more of a hollow compared to your flat back, short, low withered cob types. They tend to not have hollows at all.
This, then leads us to another question - are the hollows caused by confirmation and should we just accept it as a conformational difference? The answer to that is no, because there's something else that can cause these hollows and that's posture.
3. Poor Posture
Poor posture, specifically caused by a forward and down positing of the thorax and weak thoracic sling muscles are the most common cause of a hollow behind the scapula. It’s really interesting that the position of the thorax between the front legs can influence the size of the hollow.
Very often if you have a horse with large hollows behind the scapula, if you get them to lift up their thorax between the front legs, the hollow can almost instantly disappear. Drop the thorax back down again and the hollow reappears.
Posture Test
Here's how to test if your horse's hollows are caused by poor posture:-
With your horse standing square
Place the flat of your hands on your horse's sternum. One hand behind the front leg and the other hand goes in front of the foreleg.
Push up and back towards the withers encouraging your horse to alter the position of the thorax.
Push up and release, keeping your hands in contact.
Keep repeating the movement in a rhythm, pushing up and release, in time with your breath. Up for two - three seconds, and release.
With the repetition of the pressure and release, your horse may get into a little bit of a sway and relax.
As you do this exercise, keep an eye on the hollows behind the scapula - do they disappear or alter in anyway? If they do, it could be an indicator that they are caused by postural position.
There are a number of other exercises you can try, including the sternum scratch, which is in the Pilates book, and it's explained in the Pilates webinar too. In this on-demand webinar, Gillian explains how her equine based conditioning system can increase core stability, strength, flexibility, coordination and body awareness.
By performing these specific exercises, the core muscles that make for good posture, a strong back and assist in carrying the weight of the rider can be strengthened.
Another favourite and a good test for the position of the thorax is called the Tai-Chi.
If you want to learn more about this and other exercises to improve the problem. Check out the Thoracic Sling Muscles - Improving Posture and Movement webinar. This webinar goes
into detail about the anatomy of the muscles that help to lift the thorax and the biomechanics and exercises that you can do, both ridden and in-hand Pilates type exercises that will improve the hollows.
The Impact of Poor Saddle Fit
Another important factor to consider is saddle fit. If you have a poorly fitting saddle which is uncomfortable, this is going to contribute to the position of the thorax going forwards and down between the front legs. If the horse is effectively cringing away from an uncomfortable saddle this is further going to affect back posture and the position of the thorax, so it's going to affect the entire balance of all of these muscles, as well as affecting the posture. If you are concerned about the fit of your saddle, ask your qualified saddle fitter to come out and check it for you.
Discover More at a Lecture Demo
You can watch some of these exercises and learn more about the importance of good posture at our live painted horse lecture demonstrations. See first hand how these exercises impact the horse's posture - in a good way. Learn the value of performing these exercises, as well as gaining a deeper understanding of how the horse works and what your can do to improve comfort to boost performance.
Our next lecture demonstration is on Saturday 21 September at Moulton College, Northamptonshire. Tickets are on sale now!
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