The thoracic sling is a crucial component of a horse's muscular system, playing a vital role in its overall movement and well-being. Composed of specific muscles and other tissues that connect the front limbs to the thorax, the thoracic sling contributes significantly to a horse's balance, coordination, and strength.
Let’s take a closer look at what makes up the thoracic sling, the muscles involved, its benefits when conditioned properly, signs of weakness, and exercises to improve its strength.
What is the Thoracic Sling?
Horses differ from humans in that they don’t have a collar bone. Instead the shoulders are connected to the body by fascia, ligaments and muscles. This group of tissues is known as the thoracic sling. It lifts the thorax and holds the chest between the front limbs.
The lack of clavicle gives the shoulder more range of motion. “The larger proximal muscles activate in a complex coordination to position and stabilise the shoulder and elbow joints during ground contact.” (1) Additionally, The proximal locomotor system of the forelimbs, specifically the musculotendinous units, work to provide energy storage and shock absorption in the stance phase. (2)
The thoracic sling allows for much of the horse’s movement giving it the ability to move in multiple directions such as forward and turning, bending, jumping and more. Because of its function, a well conditioned and functioning thoracic sling is essential for overall body soundness and performance.
Muscles Involved in the Thoracic Sling:
1. Pectorals
There are four pectorals:
- transverse pectoral
- ascending pectoral
- subclavius
- descending pectoral
Illustrations by Alexa McKenna BVM & S from the book Horse Movement, Structure, Function and Rehabilitation by Gail Williams PhD
2. Serratus Ventralis
3. Rhomboideus
4. Trapezius cervicis
5. Trapezius thoracis
6. Latissimus
7. Brachiocephalicus
8. Omotransversarius
9. Sternocephalicus
Illustrations by Alexa McKenna BVM & S from the book Horse Movement, Structure, Function and Rehabilitation by Gail Williams PhD
Benefits of a Well-Conditioned Thoracic Sling
When properly conditioned, the thoracic sling enhances a horse's performance in various ways:
1. Improved Balance
2. Enhanced Coordination
3. Stability
4. Improved limb movement and stride length, reducing risk of lower limb lameness
5. Improved posture when at rest and during exercise
Recognizing a Weak Thoracic Sling
A weak thoracic sling can have effects on the entire body and function of the horse. It can cause poor gait, which can lead to dysfunction in the limbs and increase the risk of lameness.
Modern horse management, riding style, not enough free movement, and tense, consistent high head carriage will create dysfunction in the body and weakness in the thoracic sling. (2)
Signs of a weak thoracic sling may include
1. Difficulty in Turning
2. Lack of Engagement and push from the hind end
3. Tendency to "Fall In"
4. Body soreness
5. Falling on the forehand
6. Girthiness can indicate soreness cause by a weak thoracic sling
7. Struggling to navigate hilly terrain
8. Performance such a tiring more quickly while exercising
9. Reduction in flexibility and length of stride
10. Cross cantering and/or difficulty in picking up the correct lead
11. Hollow posture when exercising
12. Poor balance
While the above signs can indicate thoracic sling weakness, they can also relate to other potential issues.
Exercises to Strengthen the Thoracic Sling
1. Raised cavaletti work
Setting up raised cavaletti encourages the horse to lift its legs and stretch its head down and out, engaging the thoracic sling muscles.
2. Pole work
Pole work is fantastic for improving the thoracic sling. It can be done in hand during the early stages of rehabilitation and increase in complexity as there are improvements and you move to ridden work.
3. Hill work
Riding the horse uphill prompts the engagement of the thoracic sling. This does not need to be fast work to get results. Plenty of slow work in hand and undersaddle at the walk will slowly build the thoracic sling
4. Backing up
Backing up a few times in hand on a daily basis encourages the horse to use its thoracic sling muscles more correctly. The horse should be allowed/encouraged to lower its head during this exercise.
3. Lateral Work
Incorporating lateral exercises such as leg-yields and shoulder-in when the horse is ready can further strengthen the thoracic sling and connected muscles.
Taking time to work through beneficial exercises, such as above will help the horse develop correct muscle function, better posture and reduce wear on the anatomy of the lower limbs.
Final Thoughts
Understanding and addressing the importance of the thoracic sling in a horse's musculature is essential for promoting optimal performance and preventing injuries. Regular, targeted exercises can contribute to the development of a strong and resilient thoracic sling, ensuring a horse's overall well-being.
Resources
- 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
https://www.americanfarriers.com/articles/14163-what-is-the-horses-thoracic-sling
- 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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