The “sit bones,” officially known as the Ischial Tuberosities, are the primary weight-bearing points of the human body when seated. These bony prominences play a fundamental role in governing both comfort and stability. Understanding the location and function of the sit bones helps improve posture, minimize discomfort, and ensure the skeletal system is properly supported during long periods of sitting.
The Anatomy of the Sit Bones
The sit bones are the large, thick, roughened projections found at the very bottom of the pelvis. Specifically, they are part of the ischium, which is the lower and posterior section of the hip bone. There is one ischial tuberosity on each side of the pelvis, and they are designed to make direct contact with a seat surface.
The structure of the Ischial Tuberosity is a robust, somewhat rounded prominence that serves as an attachment point for several muscles and ligaments. This includes the three hamstring muscles (biceps femoris, semitendinosus, and semimembranosus) and the sacrotuberous ligament. When a person stands, the gluteus maximus muscle covers the tuberosity, but when the hip is flexed in a seated position, the bone becomes uncovered and directly bears the body’s weight.
How Sit Bones Affect Posture
The Ischial Tuberosities are structured to support the majority of the body’s weight when seated, acting as a stable base for the spine. When a person sits correctly, the weight is balanced evenly on these two bony points, which helps the pelvis maintain a neutral position. This neutral pelvic tilt allows the spine to stack upward with its natural curves intact, minimizing the effort required from muscles to hold the body upright.
Slouching occurs when a person rolls their pelvis backward, shifting the body’s weight off the sit bones and onto the sacrum and coccyx (tailbone). The tailbone is not designed to bear weight, and this posterior pelvic tilt causes the lower spine to round, leading to misalignment and strain on the back muscles. Conversely, maintaining an upright posture balanced directly on the sit bones reduces muscular effort and promotes healthy spinal alignment.
Practical Tips for Locating and Protecting Them
A simple way to locate your sit bones is to sit on a firm, flat surface and slide your hands, palms up, underneath your buttocks. You will feel two distinct, hard, rounded points pressing into your fingertips; these are the Ischial Tuberosities. Once located, gently rock your pelvis forward and backward to feel the shift in weight distribution and identify the neutral point where you are sitting directly on top of them.
Protecting the sit bones involves choosing seating that supports this natural alignment without causing excessive pressure. Seating that is too soft or overly padded can cause the pelvis to sink and roll backward, while surfaces that are too hard or narrow can lead to localized discomfort. Prolonged, excessive pressure on the area can irritate the ischial bursa, a small fluid-filled sac that acts as a cushion, potentially leading to a painful condition called ischial bursitis. Taking regular breaks to stand and stretch also helps alleviate pressure on the sit bones and surrounding soft tissues.