Final answer:
The lower leg moves back and up towards the buttocks during seated knee extension, with the thigh moving down, back, and twisting inward, demonstrating the knee joint's functionality which allows for bending, straightening, and pivoting.
Step-by-step explanation:
During the seated knee extension, the lower leg moves in a specific pattern. This involves the back of the lower legs moving up and back toward the buttocks, similar to the motion when kneeling. In addition, the thigh moves down and back, and there is also an inward twist of the thigh and lower leg. This is an example of how the knee joint operates like a , which allows for bending and straightening of the lower leg. As per Figure 9.36, the knee joint's function is essential for sitting, standing, and pivoting movements. Furthermore, the back of the lower legs assists in moving the thigh diagonally upward and outward.