The buttock, or gluteal region, is the rounded, fleshy area positioned posterior to the pelvis and upper thigh. This area is defined by a thick layering of muscle and adipose tissue that connects the trunk to the lower limbs. It serves as a powerful engine for human movement and upright posture, allowing for complex movements like walking, running, and maintaining balance.
Key Muscle Groups and Location
The most prominent structures of the buttock are the three layered gluteal muscles: the gluteus maximus, gluteus medius, and gluteus minimus. The gluteus maximus is the largest and most superficial, forming the bulk of the buttock’s shape. This massive muscle originates from the posterior surface of the ilium, the sacrum, and the coccyx, before inserting into the iliotibial tract and the gluteal tuberosity of the femur. Its large size makes it the body’s heaviest muscle, designed for generating immense force.
Beneath the gluteus maximus lies the fan-shaped gluteus medius, which is substantially smaller and positioned on the outer surface of the pelvis. The medius muscle originates on the outer surface of the ilium and inserts onto the lateral surface of the greater trochanter, the bony prominence at the top of the femur. This deeper position allows it to act as a precise controller of hip movement and stability. The smallest and deepest of the three is the gluteus minimus, which sits directly underneath the gluteus medius.
The gluteus minimus shares its origin on the ilium and its insertion on the greater trochanter with the gluteus medius. These two smaller muscles work in synergy, sharing the general function of stabilizing the hip. Deep to the gluteal muscles, a smaller group of muscles, including the piriformis, act primarily as lateral rotators of the hip joint.
Essential Biomechanical Roles
The primary biomechanical function of the gluteal muscles is to facilitate powerful hip extension, carried out largely by the gluteus maximus. Hip extension is the act of moving the leg backward, which propels the body forward when walking, running, or climbing stairs. The gluteus maximus also provides the necessary acceleration when standing up from a seated position or lifting an object off the ground.
Beyond extension, the gluteal muscles control the rotation of the hip joint, which helps direct the foot during movement. The gluteus maximus is a powerful external, or lateral, rotator, helping to turn the leg outward. Conversely, the anterior fibers of the gluteus medius and minimus contribute to internal, or medial, rotation of the thigh.
A particularly important role of the gluteus medius and minimus is stabilizing the pelvis during single-leg stance, such as when walking. As one foot lifts off the ground, these muscles on the stance leg contract to prevent the pelvis from dropping down on the side of the lifted leg. This action, known as hip abduction, maintains a level pelvis and is necessary for efficient locomotion. Furthermore, the substantial muscle and fat padding provides a natural cushion, distributing pressure and supporting the weight of the upper body while sitting.
Common Musculoskeletal Issues
The buttock is susceptible to several common musculoskeletal issues involving pain and dysfunction. One frequently encountered condition is Deep Gluteal Syndrome (DGS), which describes pain caused by the compression or entrapment of the sciatic nerve. Historically, this was often referred to as Piriformis Syndrome, linking the nerve compression to the deep piriformis muscle. The resulting discomfort is a shooting, burning pain that radiates down the back of the thigh and sometimes the calf.
The greater trochanter, the large bony prominence on the side of the hip, is an attachment site for the gluteus medius and minimus tendons. It is covered by bursae, fluid-filled sacs that reduce friction. Inflammation of these tendons or the associated bursa leads to gluteal tendinopathy or trochanteric bursitis, respectively. This condition results in localized pain on the side of the hip, often aggravated by lying on that side or by physical activities like walking or running.
Muscle strain is another common issue, particularly affecting the gluteus maximus due to its role in high-force activities. A strain occurs when muscle fibers are overstretched or torn, often during explosive movements like sprinting or jumping. Prolonged weakness of the gluteal muscles, sometimes associated with excessive sitting, can lead to chronic issues like lower back pain or altered knee biomechanics. This weakness forces other muscles, such as the hamstrings, to compensate for the lack of gluteal power, increasing the risk of strain in those areas.