A “square bum,” often described as an H-shape, is a common body silhouette where the line from the hip bone to the outer thigh appears relatively straight instead of curving outward. This shape results from the complex interplay between the underlying skeletal structure, the volume and tone of the gluteal muscles, and the body’s specific pattern of fat storage.
The Influence of Bone Structure
The foundational shape of the buttocks is set by the pelvis and the femur, which are the two largest bones in the region. The width of the pelvic bone, specifically the distance between the hip bones known as the biiliac breadth, establishes the upper limit of the hip span. Individuals with a wider pelvic structure may have a naturally broader base, which can contribute to a squarer appearance if combined with other factors.
The angle at which the femur, or thigh bone, connects to the hip socket also plays a role in the contour of the hip. A greater trochanter, which is the bony bump at the top of the femur, may be more pronounced in some individuals, creating a slight indentation or “hip dip” that emphasizes the straight line of the square shape. These bony structures are fixed by genetics and growth, meaning the underlying skeletal frame is largely unchangeable through lifestyle modifications.
Muscle Mass and Gluteal Contours
The gluteal muscle group, consisting of the gluteus maximus, medius, and minimus, sits atop the bone structure and significantly shapes the buttocks’ final contour. The largest of these, the gluteus maximus, primarily contributes to the overall projection and size of the rear. However, the smaller gluteus medius and minimus, located higher on the hip toward the sides, are crucial for creating the desired upper curve.
Underdevelopment or low tone in the gluteus medius can contribute directly to the square profile by failing to provide fullness beneath the waistline. This muscle’s function is to stabilize the pelvis and abduct the thigh, and when it is weak, the area may appear flatter or straighter from the hip bone downward.
A sedentary lifestyle involving prolonged sitting can lead to muscle atrophy and poor activation of these stabilizing muscles. Targeted exercises that strengthen the gluteus medius, such as side leg raises and hip abductions, can build volume in the upper, lateral hip region, which helps soften the square outline.
How Fat Distribution Affects Shape
Fat distribution is a third major factor that influences buttock shape, determined largely by genetics and circulating hormones. This adipose tissue, specifically subcutaneous fat, is deposited underneath the skin and over the muscles, providing the soft contours of the body. The square shape is often associated with a pattern where fat storage is concentrated around the upper flanks and lower abdomen, sometimes referred to as “love handles,” rather than evenly distributed across the gluteal area.
If the body tends to store fat below the hips and around the upper thighs, but not much high on the sides of the glutes, it can emphasize the straight line from the hip bone to the thigh. The female hormone estrogen encourages the storage of fat in the gluteofemoral region, which includes the hips, thighs, and buttocks.
Conversely, a lower estrogen-to-testosterone ratio or genetic predisposition to store fat in the abdominal area can result in a less rounded, more linear profile. The specific placement of this fat tissue, whether high or low on the glutes, is what either rounds out the shape or leaves the straight, square transition.
The appearance of a square bum results from a combination of three factors: the width and angle of the skeletal structure, the development level of the gluteal muscles, and the genetically determined pattern of adipose tissue placement. While the skeletal foundation is fixed, muscle development and fat distribution are modifiable, offering avenues for altering the overall contour.