A bit of Anatomy first 🦴
🐎 A horse’s movement and posture rely on the coordinated action of two major muscle systems:
The Flexor Chain – running along the ventral line beneath the spine, extending along the ventral cervical region, in front of the hips, including the abdominal muscles. These muscles flex the hips, vertebral joints, and cervical spine, elevate the back and withers, and lower the head. They are essential for maintaining spinal posture, facilitating collection, and enabling controlled engagement.
The Extensor Chain – running along the dorsal line of the spine, neck, and hindquarters, including the epaxial muscles. These muscles extend the vertebral column and hips, elevate and stabilise the back and neck, and provide propulsion during movement.
🦴Together, the flexor and extensor chains are core components that help maintain spinal alignment, balance, and fluid, controlled locomotion.
❤️🩹Muscle chains also help explain compensation patterns: a restriction in one muscle can affect movement and function elsewhere along the chain.
Extensor chain consists of:
Rhomboideus
Splenius
Longissimus dorsi
Gluteal
Hamstrings - Biceps femoris
Semitendinosus
Semimembranosus
Digital Flexor muscles
Flexor chain consists of:
Sternomandibular
Brachiocephalic
Pectorals
Abdominals – rectus abdominae,
Transverse abdominal
Internal and external abdominal oblique muscles.
Iliopsoas - Psoas Major
Psoas Minor
Iliacus
Tensor Fascia Late
Quadriceps – rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius
Digital Flexor muscles
When the extensor muscle chain is short and tight which is what this pony has, the flexor chain is long and weak. Leading to compromised postural alignment, and so any additional load imposed by the tack and rider is likely to exacerbate spinal extension. This excessive extension initiates a cascade of compensatory biomechanical adaptations that negatively influence locomotor function. Increased spinal extension not only decreases the interspinous distance between the dorsal spinous processes—thereby predisposing the animal to back pathologies—but also alters normal spinal kinematics. Such alterations disrupt the coordination of axial and appendicular movements, leading to maladaptive force distribution across the musculoskeletal system and increased stress on joints.
To optimise optimal biomechanical function, the extensor and flexor muscle chains must be in balance.
This line drawing above was taken with permission from a horse I was asked to assess and treat.
So, what were just some of the problems that I found?
· Back tension
· Neck tension
· Poll tension
· Tight shoulders
· Tight hamstrings
· Weak thoracic sling
· Weak abdominals
· Poor gait function
· Poor proprioception
· Poor stability
Sadly, all these issues can predispose this pony to injury and disease if they are not addressed.
Interaction Between Flexor and Extensor Chains
These two muscle chains function in coordination: a strong flexor chain, including the abdominals, stabilises and supports the back, while the extensor chain generates propulsion. An imbalance—such as a weak flexor chain—can cause the back muscles to compensate, leading to stiffness, discomfort, and an increased risk of injury.
If you’d like to read more on the back muscles that compensate you can check this out here https://theequinesportstherapist.co.uk/dmes-%26-stability
✨ Things to Reflect on When Observing the Above Image
🐎When asking your horse to back up, take note of the head and neck position — could this be creating more extension than you realise?
🐴Consider how your horse eats. If hay is offered from a wall-tied net, each small pull through the holes creates subtle, repetitive forces through the neck and spine. Over time, this could influence the alignment of the spinous processes and how the supporting muscles develop.
🏇🏻When training focuses mainly on achieving an “outline” — through aids or consistent pressure on the reins — we may unintentionally create tension or compensatory movement patterns instead of true postural strength.
💓💪🏻 Encouraging correct posture and balanced muscle development through thoughtful management, and progressive training allows the horse to build the strength needed to carry a rider with comfort, stability, long-term soundness and the least compensatory adaptations.
💪🏻💓As an equine strength and conditioning coach, I’m dedicated to helping horses develop deep, functional strength that supports their backs from the inside out. My focus is on creating true stability — building the right muscles to carry the weight of tack and rider with balance and ease. By reducing compensations and improving posture, I help horses move more freely, comfortably, and confidently in their work. 🐴