Buttocks

The buttocks are two rounded masses of muscle and adipose tissue located in the lower rear part of the torso, between the waist and thighs. They consist of large muscles, subcutaneous fat, and skin. Beneath them lies the pelvis, specifically the bone called the ischium, on which people sit.

The buttocks play an important role in bipedalism. The muscles there support upright posture and are among the anatomical features that distinguish human skeletal structure from that of other walking animals.

Anatomy

The largest muscle in the buttocks is the gluteus maximus, which is among the largest muscles in the body. It is followed by the gluteus medius and gluteus minimus, which lie deeper and help stabilize the pelvis when a person stands on one leg. These muscles originate from the ilium and attach to the femur.

The subcutaneous fat gives the buttocks their shape and softness. The size and amount of this fat varies considerably among individuals and is influenced by genetics, hormones, age, and diet. From an evolutionary perspective, women tend to accumulate more fat in this region than men, a pattern associated with the hormone estrogen.

Function

The gluteus maximus extends the thigh at the hip; it is used when a person climbs stairs, runs, or rises from sitting. During normal walking, its activity is minimal, but it increases when carrying a heavy load. The middle and smaller gluteal muscles prevent the pelvis from tilting toward the unsupported leg.

The buttocks are also where the body distributes weight when sitting, with the fat and muscles supporting the weight of the ischium. Additionally, the gluteus maximus is a common site for intramuscular injections and vaccinations because of its bulk; however, the lower inner region must be avoided due to concern for the sciatic nerve.

Culture and society

The shape of the buttocks is associated with bodily beauty in many cultures, and standards of attractiveness vary over time and place. Clothing, such as skirts and trousers, is often designed to accentuate this area. The buttocks are also among the body parts that many cultures associate with modesty, affecting dress codes and conventions of speech.