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Understanding the Thoracic Sling

Horses possess tremendous athletic ability, achieving feats that never cease to amaze us as their caretakers and partners. The tasks we ask our horses to perform come with high stress to the equine's anatomy, particularly a set of muscles that function much like that of the human "core muscles". Enter the equine thoracic sling.


The thoracic sling is complex apparatus that functions as the "control center of balance" in the horse. Without it, a horse quite literally could not bend, move side to side, nor balance himself for the movements horses must make in everyday life. The "sling" is named as such due to the horse relying on muscles that behave like "slings" primarily suspended between a horse's front limbs, rather than a clavicle (collar bone).


Photo credit - Canadian Horse Journal


A weakened thoracic sling is not to be taken lightly, yet there are hundreds of horses at nearly every sporting event and in every discipline with weak thoracic slings, often unbeknownst to their caretakers. The consequences of this apparatus being out of balance or weak, in terms of muscle development and overall flexion and stability can be devastating to the horse long term. They can also cost a horse person points, time and performance in the arena and out as the horse will not be able to fully extend, bend and be as agile as is necessary for the job intended.


Let's break down this complex apparatus and get to know how it works, and how we can help our horses strengthen this important part of the anatomy.


What Is It? The thoracic sling is essentially the group of muscles that make up for the horse's lack of collar bone or clavicle. This apparatus, which is made up of fascia, ligaments and muscles lifts the thorax and holds the equine chest between the front limbs. The thoracic sling works to provide shock absorption and help with the horse's overall balance in motion. These muscle groups allow the horse to move in multiple directions such as bending, turning, lowering the body (such as in reined cow horses), dressage movements, jumping and more.


The thoracic sling is comprised of the following group of muscles (pictured): all four pectoral muscles, sternocepahlicus, brachiocephalicus, omotransversarius, latissimus, trapezius thoracis, trapezius cervicis, rhomboideus, and the serratus ventralis muscles.


Photos courtesy of Illustrations by Alexa McKenna BVM & S from the book Horse Movement, Structure, Function and Rehabilitation by Gail Williams PhD


Why is it so important?

A well-conditioned thoracic sling which functions much like the core of the horse, will significantly improve the horse's overall balance, stability, stride length, and posture. It will also afford enhanced coordination and reduce the risk of lower limb lameness.


Horses are not built vertically like us, so they have a horizontal plane that requires special mechanisms allowing them to remain in balance, defying gravity.


Horses do not only require strong well conditioned thoracic slings for the work we ask of them. With nearly 80% of domestic life spent grazing or browsing, the way in which a horse carries himself while at rest, such as when he is grazing matters. I have discussed at length the impact that certain grazing or feeding positions will affect equine posture and muscle health in a separate article here.

Images reflect same horse, with completely different postures.


What causes a weak thoracic sling? Underdevelopment in the muscles can happen due to trauma or dysfunction. Believe it or not, many horses have scar tissue in the pectoral muscles. Imbalances of the body can also contribute issues such as those caused by genetics (breeding) and poor conformation. Still another issue is the simple fact that horses were not made to be ridden. We ask them to do tasks that are quite unnatural to them and place a great deal of stress on their bodies. Feeding habits or equipment used can also play a role such as feeders that are not conducive to correct, healthy posture or saddles that do not fit.


Some of the signs of a weak thoracic sling are:

  • General body soreness

  • Heavy on the forehand

  • Girthiness or cinchiness

  • Struggle with hills or incline

  • Lack of hind end engagement (drive)

  • Turning is difficult

  • Bending and flexibility is reduced

  • Reduced stride length

  • "Hollowed Out" posture when in work

  • Difficulty taking the correct lead

  • Lack of endurance ; tiring quickly while exercising

  • Poor balance


What can be done to improve thoracic sling strength for our horses?

There are many exercises and stretches that I can recommend but I've listed just a few here that tend to get the job done with increased duration and repetition. (You won't get results if you aren't consistent so daily routine is key here). Begin with just a short session, and work up to longer durations of these exercises as your horse's strength improves.


Carrot stretches are your friend.

Forward: Ask the horse to lean as far forward as possible, as you hold out a carrot or treat extended out directly in front of him.

Under: Place carrot or treat between horse's front legs just behind the carpus (many people call this the knee) and gradually lower as horse brings his head down and underneath himself.

Side Flexes: Hold carrot or treat about halfway down your horse's body near his barrel and ask horse to bring his head round flexing as far as he can left and then as far as he can to the right.


Walking Over Raised Objects.

This is an excellent strengthening exercise that serves multiple purposes beyond aiding the thoracic sling which is why I recommend it for most clients. Walking your horse over logs, raised cavalettis or other slightly raised objects is perfect for engaging the sling muscles.



Poles on the Ground.

This exercise may be done in hand or in the saddle. Simply walk your horse over ground poles and repeat in different patterns. This engages the muscles in the sling and throughout the body.


Back Up.

In general, I teach backing up as an essential part of horsemanship for many different reasons but all are helpful in the horse's overall health and flexibility. Horses should lower their heads for this exercise and this can be done on the ground or under saddle but I prefer to do this on the ground because I can see exactly how my horse is lowering his head while standing in front of him. Ask him to back up a few times each day to engage the thoracic sling correctly.


Lateral Flexion.

Anything that encourages your horse to move laterally is going to help him engage and strengthen the thoracic sling. You can ask him to do leg yields, half passes, side passes or shoulder-in. This can be done in hand, at liberty or under saddle as well. Obviously rider weight will increase the strength required.


Working Up Hill.

Hills are great for many muscles within the body, but going uphill in particular is a wonderful way to gradually strengthen the thoracic sling. You can start with mild incline and gradually work your horse into steeper slopes. This is easily done in hand or under saddle making it easy to do each time you're with your horse so long as there is a bit of a hill or incline to work with.


In conclusion, the equine muscular system is extravagant and complex to say the least. Because we are asking our horses to do work that they were not designed to do, we must help them along by addressing common issues in order to prevent body lameness, lower limb lameness, and ultimately to keep our horses comfortable and healthy.

If you have questions or need help with your horse's thoracic sling or bodywork management please feel free to reach out.


Sources:

Raspa, F.;  Roggero, A.;  Palestrini, C.;  Marten Canavesio, M.;  Bergero, D.; Valle, E. (2021, March 10) Studying the Shape Variations of the Back, the Neck, and the Mandibular Angle of Horses Depending on Specific Feeding Postures Using Geometric Morphometrics. Animals 2021, 11, 763. https://doi.org/10.3390/ani11030763 (open access article). Retrieved from  https://www.mdpi.com/2076-2615/11/3/763/htm

Harrison SM, Whitton RC, King M, Haussler KK, Kawcak CE, Stover SM, Pandy MG. Forelimb muscle activity during equine locomotion. J Exp Biol. 2012 Sep 1;215(Pt 17):2980-91. doi: 10.1242/jeb.065441. PMID: 22875767.

American Farriers Journal, Hagen J, 2023 Nov, 16

Anatomy of the Horse, Klaus-Dieter Budras, fifth edition

Horse Movement, Structure, Function and Rehabilitation; Gail Williams PhD, illustrated by Alexa McKenna BVM & S


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