Functional specialisation of muscle architecture is a hallmark of all quadrupeds, including horses. Their proximal limb muscles have evolved to perform specific locomotory duties while distal muscles such as the psoas major and iliacus can economically generate large forces (see for instance psoas major and iliacus).
These muscles work isometrically to support the flexed position, hollow the back and raise the withers – they are considered hip external rotators on horses.
Gluteus Maximus
This muscle, the largest gluteal muscle, plays an essential role in hip extension (moving the thigh backwards) and external rotation of the hip joint. Furthermore, it assists with abduction (moving thigh out to side) and flexion of the hip (bent knee). Innervated by the inferior gluteal nerve.
It attaches to the Iliotibial Band (ITB) via its superior and inferior gemelli muscles – two narrow triangular muscles separated by the Obturator Internus Tendon that form two triangular sets – creating a posterior force on the ITB that acts to counterbalance any anterior forces created during hip flexion by TFL and vastus lateralis muscles.
At weight bearing, the muscle helps stabilise pelvis and femur by creating compressive forces through its deep connections with iliotibial tract and gluteal tuberosity of femur. Furthermore, this muscle plays an essential role in movement of both lumbar spine and sacroiliac joints.
Poor function of the GM can result in various symptoms, such as gluteal pain, hip stiffness and groin/buttock discomfort. This may be the result of injury or compensatory movements patterns which create altered muscle imbalances. For this reason it is crucial that you visit a physiotherapist regularly in order to strengthen and support your GM; they will help identify what factors contribute to symptoms while offering advice and solutions to address them.
Gluteus Medius
The gluteus medius is a fan-shaped muscle located on the outside of the hip. It serves to abduct legs away from you while also assisting in external rotation of the hip joint, often being described as the deltoid muscle of the hip due to its shape and actions. A decrease in gluteus medius strength has been linked with lower back pain (LBP), since this affects pelvic alignment as well as transverse plane rotation and frontal plane position of the hips.
As we walk, run, and jump the gluteus medius muscle must control our legs so as to stop them from swinging forward, when this muscle becomes weak or dysfunctional it may result in Iliotibial Band Syndrome.
Gluteus Medius muscle is supplied by the superior gluteal nerve. If this muscle becomes injured it may result in trochanteric bursitis which causes discomfort along the outside of knee and buttocks, especially with repetitive activities like walking or running, climbing stairs or weight bearing activities, such as climbing stairs. Massage therapy has proven itself helpful in treating gluteus medius dysfunction and relieving trochanteric bursitis symptoms; other treatment options may include hip flexor exercises, prone bridge/plank and single leg balance exercises.
Gluteus Minimus
The gluteus minimus is the smallest of three gluteal muscles, found deep within the posterior hip region. It is protected by gluteus medius and tensor fasciae latae muscles, and innervated by superior gluteal nerve (L4-S1). Its primary purpose is hip abduction; however it also works together with its counterparts to support single leg support in gait; weakening this muscle can result in Trendelenburg gait whereby supporting side drops as swinging leg moves forward; its weakness could lead to Trendelenburg gait, where supporting side drops as swinging leg steps forward versus supporting side drops as swinging leg steps forward despite supporting side dropping by other gluteal muscles working together in tandem.
Gluteus minimus plays an essential role in controlling hip rotation, as it has strong attachments to the joint capsule of the hip joint. It regulates capsular tension and femoral head translation during movement as well as contributing to stabilization of both the hip and spine.
Therefore, it is crucial that gluteal muscles work as one unit. Failure to activate one gluteal muscle effectively may result in other muscles compensating, often leading to hip pain. Bridge exercises provide an excellent test for both gluteus maximus and minimus as they must work in harmony to maintain neutral pelvic position and a straight spine; weighted bridges present even greater challenges as resistance may further challenge their stability during hip abduction against resistance.
Iliopsoas
Iliopsoas is the strongest hip flexor and contributes to external rotation of the femur. Innervated by direct branches from L1-L3, its formation involves joining together Psoas major and Iliacus muscles to form part of Scarpa’s Triangle’s floor.
Due to their proximity, iliopsoas tendinopathy (or snapping hip syndrome) and bursitis often coexist.
To use the Hip Hook for hip external rotation stretching, lie down and place its tip against the front of your pelvis (adductor muscle). Apply pressure to its lever for 30-90 seconds while breathing and relaxing; once your iliopsoas shifts and relaxes, release its pressure.
This exercise can be especially helpful for anyone who spends long hours sitting. It will prevent muscle imbalances that lead to poor posture and reduced mobility, strengthening hips, improving movement patterns and strengthening iliopsoas (one of our primary muscular control systems over body movements) which is essential for locomotion – just imagine trying to walk, run or crawl without this essential muscle working!
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