The buttocks are the two rounded, fleshy areas on the back of your hips, formed by a combination of large muscles, a layer of fat, and connective tissue. They sit between your lower back and the tops of your thighs, and they do far more than provide cushioning when you sit. The buttocks contain the largest muscle in the human body and play a central role in walking, running, standing, and maintaining balance.
What the Buttocks Are Made Of
Three layers of tissue give the buttocks their shape and function. The deepest layer is muscle, specifically three gluteal muscles stacked on top of each other. Over those muscles sits a layer of subcutaneous fat, which varies in thickness from person to person. Covering everything is skin, which in this region is relatively thick compared to other parts of the body.
The gluteal muscles all attach to the pelvis, a basin-shaped set of bones that connects your spine to your legs. The largest of these bones, the ilium, fans out on each side and provides a broad surface for the muscles to anchor to. The tailbone (sacrum and coccyx) also serves as an attachment point, particularly for the biggest muscle in the group.
The Three Gluteal Muscles
The gluteus maximus is the largest and most superficial of the three, and it’s considered the largest muscle in the entire body. It forms the bulk of the buttock’s shape. Its primary job is extending your hip, which means pushing your thigh backward. You use it heavily when climbing stairs, standing up from a chair, running, and sprinting. It also rotates your thigh outward and helps stabilize your knee through a thick band of tissue that runs down the outside of your leg.
The gluteus medius sits underneath and slightly above the maximus, along the outer edge of the pelvis. The gluteus minimus is the smallest and deepest of the three, tucked beneath the medius. These two muscles share a critical function: they pull your leg out to the side and rotate it inward. More importantly, every time you take a step and one foot lifts off the ground, the medius and minimus on the standing leg keep your pelvis level so you don’t tip sideways. Without them, walking would look like a pronounced waddle.
Why Humans Have Large Buttocks
Compared to other primates, humans have unusually large, muscular buttocks, and the reason comes down to walking upright. When our ancestors shifted from moving on all fours to standing on two legs, the gluteus maximus took on a much bigger role. In four-legged animals, other muscles handle most of the work of locomotion. But on two legs, the trunk and upper body sit directly on top of the pelvis, and something powerful has to keep that weight from pitching forward with every stride. The gluteus maximus does that job. Research on early human fossils shows that changes in the shape of the pelvis, specifically a wider, more backward-facing surface on the ilium, allowed the gluteus maximus to grow larger and attach in a way that made upright walking and running efficient.
Fat Distribution and Body Shape
The fat layer over the gluteal muscles is what gives the buttocks much of their visible roundness and softness. How much fat accumulates here depends on genetics, overall body composition, and biological sex. Women tend to store more subcutaneous fat in the buttocks and thighs, creating what’s often described as a “pear shape” distribution. Men tend to store more fat around the abdominal organs instead, resulting in an “apple shape.”
This difference isn’t just cosmetic. Fat stored in the gluteal and thigh region is associated with lower metabolic risk compared to fat stored around the abdomen. Abdominal fat correlates more strongly with conditions like type 2 diabetes and cardiovascular disease, while lower-body fat appears to be somewhat protective. Women’s tendency to store fat in this region is one reason premenopausal women generally have lower rates of metabolic disease than men of similar weight. At a cellular level, the fat cells in women’s gluteal and thigh areas tend to be smaller and more numerous than those found in abdominal fat, which reflects a different metabolic profile.
Nerves Running Through the Region
The buttocks aren’t just muscle and fat. Several important nerves pass through the gluteal region on their way from the spine to the legs. The most significant is the sciatic nerve, the longest and thickest nerve in the body. It exits the pelvis through an opening called the greater sciatic foramen, passing beneath a small, deep muscle called the piriformis, and then travels down through the buttock into the back of the thigh.
The sciatic nerve’s path through the buttock is the reason that pain originating in this area can radiate all the way down the leg. It also explains why medical injections into the buttock are given in the upper outer quadrant: the sciatic nerve runs through the lower inner portion, and hitting it with a needle can cause significant pain or nerve damage.
Common Causes of Buttock Pain
Pain in the buttock is often related to the sciatic nerve getting compressed or irritated somewhere in the gluteal region. For decades, this was called piriformis syndrome, since the piriformis muscle sits directly over the nerve and can squeeze it when tight or inflamed. But doctors now recognize that several different structures can trap the sciatic nerve in this area, not just the piriformis. The broader term “deep gluteal syndrome” covers all of these causes.
In a study of 239 patients with non-spinal sciatica, compression beneath the piriformis accounted for about 68% of cases. Other causes included entrapment at the opening where the nerve exits the pelvis (6%) and compression in the space near the sit bone (about 5%). Fibrous bands, blood vessel abnormalities, hamstring injuries near their attachment point, and even small masses can also press on the nerve in this region.
Doctors can often narrow down the source of gluteal pain by pressing on specific landmarks. Pain near the sciatic notch (a bony groove on the pelvis) suggests piriformis involvement. Pain to the side of the sit bone points toward the space between the hip bones. Pain on the inner side of the sit bone may indicate compression of the pudendal nerve, a different nerve that supplies the pelvic floor. Most cases respond to physical therapy, anti-inflammatory treatment, and targeted injections. Surgery to free the trapped nerve is reserved for the small number of cases that don’t improve with these approaches.
Cushioning and Sitting
The combination of gluteal fat and muscle provides natural padding over the ischial tuberosities, the two bony projections at the base of the pelvis that bear your weight when you sit. Without adequate soft tissue coverage, prolonged sitting puts direct pressure on skin and bone, which can reduce blood flow and lead to tissue breakdown. This is why people who are immobilized, whether from injury, surgery, or paralysis, are vulnerable to pressure ulcers on the buttocks. The ischial tuberosities and the sacrum are among the most common sites for these wounds. Shifting your weight regularly and maintaining adequate nutrition to support skin health are the main ways to prevent them.