Muscles that Move the Leg

The quadriceps femoris comprises four distinct muscles: the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris. These muscles merge to form the most prominent anterior compartment muscle of the thigh. The quadriceps tendon, shared by all four muscles, attaches to the patella and extends as the patellar ligament to the tibial tuberosity, enabling knee extension and thigh flexion.

The sartorius is called the tailor's muscle because it enables cross-legged sitting, a position tailors traditionally adopt while working. Located in the anterior compartment, this muscle flexes the knee and causes lateral thigh rotation at the hip joint. Its unique positioning and function make it essential for the specific posture historically associated with tailoring.

The gracilis, a long, strap-like muscle in the medial compartment, performs three primary movements: it flexes the leg at the knee joint, adducts the thigh, and medially rotates the tibia during knee flexion. As the most superficial and medial of the thigh muscles, it plays a key role in coordinating leg and hip movements.

The three hamstring muscles are the biceps femoris, semitendinosus, and semimembranosus, located in the posterior compartment. These muscles cause flexion at the knee and extension at the hip. Hamstring tears, commonly called pulled hamstrings, are frequent sports injuries due to the significant demands placed on these muscles during leg movement.

The popliteus is a small, triangular muscle located at the back of the knee that initiates knee flexion and provides joint stability. It originates from the lateral femoral condyle and inserts onto the posterior tibia surface below the knee. The popliteus causes medial rotation of the tibia, a key mechanism for unlocking an extended knee and enabling smooth flexion.

The popliteal fossa is a diamond-shaped area on the back of the knee defined by specific muscle tendons. The biceps femoris muscle tendons flank it on either side, while the semitendinosus and semimembranosus tendons border it medially. This anatomical space is crucial for understanding posterior knee anatomy and the arrangement of structures supporting leg movement.

The medial compartment contains several adductor muscles including the gracilis, adductor longus, adductor brevis, and obturator externus. The adductor longus originates from the pubis and extends to the femur's linea aspera, while the adductor brevis lies deeper with a shorter, more oblique course. These muscles work together to adduct and medially rotate the thigh, coordinating complex leg movements.