Which group of muscles are responsible for knee flexion?

The group of muscles primarily responsible for knee flexion is the hamstrings. This group includes three muscles: the biceps femoris, semimembranosus, and semitendinosus. These muscles originate from the ischial tuberosity of the pelvis and insert onto the tibia and fibula bones in the lower leg. When they contract, they pull the leg backward at the knee joint, resulting in knee flexion.

Understanding the role of the hamstrings in this function is crucial for evaluating and rehabilitating knee injuries or conditions affecting mobility. While other muscles in the options do play roles in movement and stability, they do not primarily serve the function of flexing the knee. For instance, the gastrocnemius, although it crosses the knee joint and assists in flexion, primarily serves as a plantar flexor of the ankle. Adductors are more involved in hip movements and the gluteus maximus is crucial for hip extension and stability rather than knee flexion. This makes the hamstrings the critical muscle group for this specific motion.