The Iliopsoas is not a single muscle but rather a group of three muscles seated deep within the hindquarter. It is made up of the psoas minor muscle, the psoas major muscle and the illiacus  muscle. Together they work to flex the hip and lumbosacral junction, tilting the pelvis. This is the primary step in protracting the hindlimb and therefore is susceptible to injury. Any malfunction of the psoas muscles will have a negative effect on movement and performance of the horse. The Iliopsoas Theory™ developed by Beth Shaw and Abi Lewis states that strain of the iliopsoas muscle is the most common hindquarter injury in horses and it can occur at any point in the horses life.

Horses are essentially prey animals and are therefore programmed to hide their pain to avoid being targeted by a predator. Often we as humans forget this and are only aware of obvious signs of pain and ignore subtle cues such as change in temperament or unwillingness to complete a task. In an effort to hide their pain they recruit different muscles to complete a task making it difficult to diagnose the original injury. This change in muscle recruitment often leads to further injury of other muscle groups and this is referred to as a secondary strain due to compensation. 

Poor performance and back pain often stem from weakness or restriction of the iliopsoas. A horse with a near hind iliopsoas strain will show these subtle signs

• Dropping of the near hind

• Stiff to the right

• Over bend on the left

• Stiffness in jaw on the off side

• Uneven trot on the left diagonal, may be felt as a twist of the riders back when rising

• Leg yield to the right more difficult

• Difficulty picking up right lead canter

• Lacks impulsion and forward movement

• Lacks flexibility behind the saddle