Another week, another muscle. Last week I discussed the TFL. To stay in the area of the hindquarters, this week the Middle Gluteal has the spotlight.
The Middle Gluteal is the strongest muscle of the gluteal group and largely shapes the croup of the horse. The Middle Gluteal is a superficial muscle that strongly attaches to the pelvis at the great trochanter of the femur. It has multiple origins at the Ilium, Gluteal fascia and the Dorsal Sacroiliac Ligaments as well as the aponeurotic covering of the Longissimus Dorsi Muscle – the Middle Gluteal Tongue [the portion of the muscle that goes over the last 1-4 ribs] tapers in its attachment into the Longissimus Dorsi.
Apart from a direct muscular connection, the Middle Gluteal and Longissimus Dorsi are also intimately linked through a fascial connection from the Gluteal Fascia to the Thoracolumbar fascia. Hence, it has a double connection to the horse’s thoracolumbar spine.
The Middle Gluteal also has a deeper section consisting of a separate entity called the Accessory Gluteal. Due to indecision between anatomists, the Accessory Gluteal is either absent or referred to as ‘deep’ in most anatomy textbooks. However, dissection research performed by Sharon May-Davis confirms that although assisting it in function, the Accessory gluteal most definitely should be considered as a separate muscle to the Middle Gluteal.
The main function of the Middle Gluteal is extending and abducting the hip joint. However, when the femur is fixed it also raises the trunk!
As mentioned earlier, the Middle Gluteal is a muscle that shapes the croup. In some horses, the muscle tone of the MG is hollow and thus underdeveloped [atrophied]. What can be causing this phenomom?
1️⃣ Sacroiliac Dysfunction. In case of subluxation, the MG usually atrophies first due to the fact that the origin also lies at the long and short dorsal Sacro-iliac ligaments. Thus, atrophy of the Middle Gluteal can be an important indicator in detecting SI problems earlier.
2️⃣ Spinal issues. As there is a double connection between the MG and the Longissimus Dorsi, these muscles naturally influence each other. In case of spinal issues, the connection naturally gets compromised via the Longissimus Dorsi and then also results in atrophy and dysfunction of the MG.
3️⃣ Saddle / Riders seat. Due to the connection between the MG and the Longissimus Dorsi - on which we sit (!), both saddle and rider have a direct effect on the MG. An ill-fitting saddle can cause excess pressure on the loin, which is damaging. As the aponeurosis and fascia of the MG origin can reach as far as L1, the pressure of the saddle will be centered at this area. Thus, the horse won’t be able to use this muscle to its full extent, causing atrophy. The excess pressure can also disable the extension both forward and backwards due to the pulling of the muscle at the origin, which causes discomfort.
The same can be said for a rider that sits in a so-called ‘drivers seat’. The causes great discomfort for the lower back and all its fascial and muscle connections.
Since there is no way we can completely yield our pressure on the Longissimus Dorsi when ridden, it is essential to work the horse also on the ground so restore proper functionality in these muscles and build them effectively!
A nicely developed middle gluteal muscle
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