The muscles that drive the body’s largest, most powerful movements are often located along the backside, forming what is sometimes called the posterior chain. This chain includes two large, influential muscle groups: the gluteal complex and the hamstrings. Together, these muscles generate the force required for everyday actions, from maintaining upright posture to engaging in athletic activities.
The Gluteal Complex Location and Role
The gluteal complex defines the shape of the buttocks area, acting as the primary connection between the pelvis and the upper leg bone, the femur. This complex is composed of three distinct muscles: the Gluteus Maximus, the Gluteus Medius, and the Gluteus Minimus. The largest and most superficial is the Gluteus Maximus, a thick muscle that forms the prominence of the hip and produces power.
The Gluteus Medius and Gluteus Minimus are positioned beneath the Maximus on the outer surface of the pelvis. These two smaller muscles stabilize the pelvis during movement. The primary function of the entire complex is hip extension, such as when standing up or propelling the body forward while running.
The Gluteus Medius and Minimus also manage two additional movements: hip abduction (moving the leg out to the side) and external rotation (turning the leg outward). These actions are essential for maintaining balance and ensuring the pelvis remains level.
The Hamstring Group Location and Role
The hamstring group is located directly on the back of the thigh, extending from the pelvis down toward the knee. This muscle group connects the ischium, or “sit bone,” to the tibia and fibula bones of the lower leg. The hamstrings are a trio: the Biceps Femoris (outside of the thigh), the Semitendinosus, and the Semimembranosus (both inside of the thigh).
These three muscles are categorized as “two-joint muscles” because they cross and influence the movement of both the hip and the knee. This dual connection gives the hamstrings two distinct primary functions. One function is to flex, or bend, the knee, which is the action of bringing the heel toward the buttocks.
The second function is to assist the Gluteus Maximus in hip extension. The Semitendinosus and Semimembranosus also internally rotate the lower leg when the knee is bent. This combined role makes the hamstring group highly active during explosive movements and contributes to its susceptibility to strains.
Synergy in Movement How They Power the Body
The gluteal complex and the hamstring group function as a single, coordinated engine. While each group has individual roles, they cooperate to perform compound actions requiring simultaneous movement at both the hip and the knee. This synchronization is evident during the human gait cycle, where the glutes initiate the backward thrust and the hamstrings assist in preparing the leg for the next step.
Movements like running, jumping, and standing up from a chair rely on the coordinated engagement of these muscle groups. When a person runs, the glutes are the main drivers of hip extension, while the hamstrings are engaged eccentrically to control the forward swing of the leg. If one group is weak or underactive, the other must compensate, which can lead to inefficient movement patterns or increased risk of injury.
Simple Tests to Locate and Activate the Muscles
To feel the glutes working, perform a Glute Bridge. Lie on your back with your knees bent and feet flat on the floor. The movement involves squeezing the buttocks and then lifting the hips off the floor until the body forms a straight line from the shoulders to the knees. If done correctly, the contraction should be felt in the gluteal muscles rather than the lower back or the back of the thigh.
To isolate the hamstring group, the Supine Heel Dig is recommended. Start by lying on your back with one leg bent at the knee, placing the heel on the floor. The action involves gently pushing the heel down while attempting to pull the heel toward the buttocks, keeping the foot from sliding. This isometric contraction causes the hamstrings to activate.