Flexion and extension are two key movements performed at the knee joint. Knee flexion occurs when a person bends the leg, bringing the heel closer to the back of the thigh. It reduces the angle between the femur and tibia. The range of knee flexion varies according to the position of the hip and whether the movement is active or passive. In contrast, knee extension happens when a person straightens the leg, moving the heel away from the thigh. This increases the angle between the femur and tibia