When you sit down, you likely feel the firm contact of your body with the chair. This sensation comes from what many commonly refer to as your “sit bones.” These bony prominences are a familiar part of our anatomy, serving as a primary point of contact and support whenever we are in a seated position.
The Ischial Tuberosity
The “sit bone” is scientifically known as the ischial tuberosity. It is a large, rounded, bony protrusion located at the lower, posterior aspect of the ischium, one of the three bones that fuse to form the pelvis. This structure forms the base of the buttocks and is part of the pelvic outlet. It also serves as an attachment site for several muscles and ligaments, including the hamstring muscles, a group of three muscles in the back of your thigh.
The ischial tuberosity provides attachment for various muscles. For example, the semimembranosus muscle originates from the upper part, while the long head of the biceps femoris and semitendinosus muscles attach to the lower part. The adductor magnus muscle and the sacrotuberous ligament also connect to this robust bony prominence.
Why It’s Your “Sit Bone”
The common name “sit bone” directly reflects the ischial tuberosity’s primary function. When a person sits, these bony structures bear the majority of the body’s weight. They act as the direct point of contact between the pelvis and the sitting surface, effectively distributing pressure.
The ischial tuberosity is adapted to withstand pressure and support body weight over prolonged periods. Its position helps maintain stability and posture while seated, allowing the torso to remain upright. In an upright standing position, the gluteus maximus muscle typically covers the ischial tuberosity. However, when the hip is flexed, such as in sitting, this muscle moves, leaving the tuberosity uncovered and ready to bear weight.
Common Conditions
Given its role in weight-bearing and as an attachment point for various muscles, the ischial tuberosity can be subject to certain conditions that cause discomfort. One such condition is ischial bursitis, often called “weaver’s bottom” or “tailor’s seat.” This involves inflammation of the ischial bursa, a fluid-filled sac located between the ischial tuberosity and the overlying tendons or skin. It commonly results from prolonged sitting, especially on hard surfaces, or repetitive stress to the area. Symptoms include pain and tenderness around the sit bone, which may worsen with sitting or activity.
Another condition affecting this area is hamstring tendinopathy, also known as proximal hamstring tendinopathy. This involves irritation or inflammation of the hamstring tendons where they attach to the ischial tuberosity. It is frequently observed in athletes or individuals engaged in activities involving repetitive hip flexion and extension, such as running, cycling, or sprinting. Symptoms often include deep pain in the buttocks and upper thigh, particularly noticeable during prolonged sitting, stretching the hamstrings, or during physical activity.