The hip is a complex intersection of the lower torso and the legs, involving numerous muscles that work together to produce movement and maintain stability. These muscles are responsible for walking and running, holding the body upright, and keeping the pelvis balanced during daily activities. The major muscles of the hip are best understood by grouping them according to their primary function: the powerful movements of flexion and extension, the fine control of abduction and rotation, and the stabilizing action of adduction.
The Primary Engines: Flexion and Extension
The most powerful movements of the hip are flexion and extension, which are the actions that drive forward motion like walking and running. Hip flexion, the act of lifting the thigh toward the chest, is primarily driven by the iliopsoas muscle group. The iliopsoas is a composite muscle made up of the psoas major and the iliacus, which are considered the strongest hip flexors in the body.
The psoas major originates along the vertebrae of the lower spine, while the iliacus originates across the inner surface of the pelvis. These two muscles merge and attach to the femur at the lesser trochanter, acting as the primary engine for movements like marching or rising from a chair. The iliopsoas also plays a significant role in stabilizing the lower spine and pelvis, connecting the upper body to the lower body.
Opposing this lifting motion is hip extension, the movement of pushing the leg backward, which is dominated by the gluteus maximus. This muscle is the largest of the three gluteal muscles and is the single largest muscle in the human body by volume. Its primary function is to straighten the leg at the hip, providing the force needed to propel the body forward during running or to stand up from a seated position.
The gluteus maximus is the main extensor of the hip, responsible for up to 75% of the power behind this movement. The hamstring muscles, located on the back of the thigh, also contribute to hip extension, working alongside the gluteus maximus.
The Stabilizers: Abduction and Rotation
Beyond the powerful forward and backward movements, the hip relies on smaller muscles for stability and precise control, particularly during single-leg activities. The gluteus medius and gluteus minimus are two muscles located on the side of the hip that are essential for abduction, which is the movement of moving the leg away from the midline of the body. They are both considered primary hip abductors.
The gluteus medius lies above the gluteus minimus, and both muscles attach to the greater trochanter of the femur. Their most important function is stabilizing the pelvis when a person stands on one leg, such as during the gait cycle of walking or running. When one foot is lifted off the ground, these muscles contract on the standing leg to prevent the pelvis from dropping on the opposite, unsupported side, a mechanism that keeps the torso level.
Rotational movements are managed by several muscles, including the deep lateral rotators, which are a group of smaller muscles situated deep within the buttock region. The piriformis is the most well-known of this group, acting to turn the thigh outward. The gluteus maximus also assists with lateral rotation, but the deep rotators provide the fine-tuning for this movement.
The Inner Thigh Group: Adduction
The final major group of muscles controls adduction, the action of bringing the legs back toward the center line of the body. These muscles are located on the inner thigh and are collectively referred to as the adductor group. This group includes the adductor longus, adductor brevis, and adductor magnus, among others.
These ribbon-like muscles originate on the lower portions of the pelvis and attach along the length of the femur, or thigh bone. Their primary purpose is to pull the legs together, which is crucial for maintaining balance and controlling the side-to-side shift of the body during movement. The adductor magnus is the largest and most complex of the group, with a portion of it also contributing to hip extension.
The adductor longus, brevis, and magnus work together, and a strain in one of these muscles is commonly referred to as a groin pull. While their main action is adduction, these muscles also assist with hip flexion and rotation.