09/20/2022
The equine thoracic sling is a hot topic at the moment, but what exactly is it and what is all the fuss really about?
Unlike us humans; horses (and many other quadrupeds) lack any bony attachment (collar bone) between the forelegs and the thorax (body). Instead, the thorax is suspended between the forelimbs by a ‘sling’ of muscles, known as the ‘thoracic sling’. Exactly which muscles should be included under this term is an area of some debate. In future articles I will take a more detailed look at the most commonly discussed structures; how they should function to aid efficient and healthy locomotion, and how disfunction may be impacting our horses.
The thoracic sling is made up of various muscle groups, these include:
• Muscles of the chest including deep and superficial pectoral muscles
• Muscles of the shoulder including omotransversarius, subscapularis and subclavian
• Muscles of the ribs including ventral Serratus and latissimus dorsi
• Muscles of the wither and upper neck including rhomboid and trapezius
• Muscles of the lower neck including the brachiocephalic and sternomandibular
When conditioned effectively these muscles enable the horse to elevate the thorax (body) independently within the shoulder girdle. This much coveted phenomenon can make the difference between a horse who appears croup high / ‘on the forehand’, and one who floats effortlessly with their withers and back raised, and freedom through the shoulders.
While for some horses this may seem to come naturally, conditioning of the thoracic sling requires regular activation of the correct muscles. Many horses develop poor or weak posture from a young age, this may be due to conformational weaknesses or injury; but I believe that lack of active engagement of the thoracic sling muscles in daily movement is also a significant factor.
Modern management practices often leave horses stood for prolonged periods in stables or small paddocks, with limited variation of terrane and forage. This can result in horses who no longer use their bodies as nature intended; to balance up and down hills, stretch to reach browse nor walk for vast distances in search of food.
Over time muscles which are not regularly used will weaken and atrophy, resulting in overall postural changes and reduced performance. It is therefore essential that we assess the impact modern husbandry may be having on the development of our horses, and consider the implementation of environmental enrichment where ever possible; as these can have a greatly beneficial impact on long term movement patterns and postural development.
The muscles of the thoracic sling enable the forelimbs to move inwards or outwards from the body, shifting the centre of mass or balance from one forelimb to the other. This allows the horse to turn and manoeuvre efficiently at speed and when effectively conditioned, enables the horse to perform lateral movements from a basic leg yield, to the canter half-pass and pirouette.
In addition, these muscles control the movement of the scapula; both forwards and back, up and down (as well as towards and away from the body), while maintaining the integrity of its connection at the wither, absorbing concussive forces from limb impact and (in the case of the thoracic serratus ventralis) storing and returning elastic energy to aid efficient movement. It is therefore of vital importance that the thoracic sling is able to work effectively; without restriction or discomfort.
Regular assessments from a qualified body worker can help pick up any tension or restrictions which may be occurring through the muscles of the thoracic sling. Addressing issues early on will reduce the risk of injury occurring, and enable the horse to build healthy posture and maintain long term soundness.
