Knowing about a horse’s muscles gives you a better understanding of its movement, locomotion and comfort. Each muscle plays a specific role in propulsion, balance, flexibility and posture.
Let’s take a look at the 10 most essential muscles for any rider, practitioner or enthusiast who wants to refine their understanding of equine biomechanics.
The latissimus dorsi: the bridge between the hindquarters and the forehand
The latissimus dorsi connects the horse’s back to its foreleg. It is a large triangular muscle located under the saddle, between the withers and the last rib.
Its function? To flex the shoulder and pull the limb backwards. It plays a key role in propulsion: it helps to transmit power from the hindquarters to the forehand. A latissimus dorsi that is too tense limits shoulder opening and shortens the stride.
Conversely, a relaxed muscle promotes freedom of movement and raises the back. It is therefore a muscle that needs to be maintained through stretching and relaxation exercises.
The trapezius: guardian of shoulder freedom
Located around the withers and upper neck, the trapezius has two parts (cervical and thoracic).
Its role is to raise and mobilise the shoulder blade, contributing to scapular suspension and stability of the thoracic girdle.
A supple and active trapezius gives the horse a free neck and a mobile withers, which are essential for posture and fluidity of movement.
When tense, the withers freeze: locomotion becomes stiff and the topline locks up.
The gluteus maximus: the engine of propulsion
It is impossible to talk about horse muscles without mentioning the gluteus maximus, the horse’s true powerhouse.
It is the main engine of posterior thrust, located on the croup, forming a clearly visible rounded mass.
It extends the hip and propels the horse forward. Weakness in this muscle often results in a loss of thrust, difficult upward transitions or an asymmetrical pelvis.
Working on varied terrain, with ascents and descents, helps to strengthen this fundamental muscle group.
The biceps femoris: the pillar of propulsion and stability
This large lateral thigh muscle acts on the hip, stifle and hock. It coordinates the movement of the entire hindquarters.
The biceps femoris is therefore essential for pelvic stability and propulsion.
When it contracts excessively, the stifle loses mobility and the horse has difficulty engaging.
Good forward movement and flexibility work is essential to keep this muscle functional and supple.
The long triceps brachii: the key to anterior stability
Between the shoulder and the elbow, the long triceps brachii plays a major role in stabilising the forelimb during the support phase.
It extends the elbow and acts as a shock absorber each time the horse lands on the ground.
When it is painful, irregularity in the front of the leg or even slight limping is often observed. Regular exercise on soft ground, without overload, helps to maintain muscle tone without generating tension.
The sternocleidomastoid: the muscle responsible for head posture
The sternocleidomastoid is located below the throat, on either side of the windpipe.
It flexes the neck and pulls the head downwards and to the side.
It is an indicator of cervical tension: in horses that lean on the bit or hood themselves, it often becomes hypertrophied.
Overuse of this muscle disrupts the horse’s balance and blocks neck mobility. It works in opposition to the splenius to maintain proper cervical-thoracic balance.
The splenius: balance and lightness of head carriage
At the back of the neck, between the nape and the shoulder, the splenius is an essential stabiliser of the upper neck.
It raises and extends the head, contributing to the horse’s longitudinal balance.
A relaxed splenius promotes lightness in the hand and suppleness in bends.
When tense, on the other hand, the neck becomes rigid, making the horse more difficult to position or bend.
The abdominals: core strength for the back
The abdominals (obliques and rectus abdominis) play an often-underestimated role: they support the back and actively participate in engaging the hindquarters. Located along the ventral line and flanks, they stabilise the spine and help lift the chest between the shoulders.
A horse with weak abdominals will tend to hollow its back and lose its unity.
Conversely, a horse with good core strength has a strong back, capable of supporting the rider and moving in the correct posture.
Transition exercises, ground bars and hill work are excellent for strengthening this area.
The longissimus: the spine of movement
The longissimus dorsi runs along the spine, from the withers to the croup. It is the key muscle of the back, often the site of tension.
It stabilises and extends the spine, transmits the thrust of the hindquarters forward and ensures continuity of movement.
A horse experiencing pain in this area will show a loss of momentum, stiffness in the back or a frozen back.
Good relaxation of the longissimus is a sign of a relaxed horse that is comfortable in its body.
The pectoral muscles: the basis of front/back balance
Located at the base of the chest, the superficial and deep pectoral muscles connect the thorax to the front limbs.
They enable the limb to be brought back under the body and contribute to propulsion and suspension.
They also play a major role in front-to-back balance.
When they are tense, the shoulders lock up, the horse has difficulty ‘raising its withers’ and its overall balance is affected.
Also good to know
• Deltoid: involved in shoulder movement.
• Semitendinosus/semimembranosus: essential for propulsion and pelvic stability.
• Masseter: involved in masticatory balance and influences mandibular tension.
Understanding muscle synergy for a harmonious horse
These ten muscles never work alone. They form a complete myofascial chain, where each link influences the others.
A simple tension, weakness or pain in one of them can unbalance the horse’s entire movement: loss of range of motion, stiffness, hollow back, asymmetry…
Working a horse in a relaxed manner, with hindquarter engagement and an arched back, helps to preserve this muscular harmony.
This is the secret to a balanced, high-performing horse that is comfortable in its own body.
To learn more, check out the book ‘Understanding Horse Myology’ by Julia Prevel. This comprehensive work teaches you how to observe and analyse your horse’s musculature, with detailed diagrams and explanatory text for each muscle.