A person executes a knee extension. The fitness instructor wants to analyze the force requirement on four different positions. The weight of the external weight along with the weight of the tibia and foot is 40 lbs, so Weight W-40lbs. The line defined between the Knee and the Center of Mass (CoM) (of the tibia-foot-and external weight system) is measured and it is Knee_to_Com = 25 inches. Position A is the starting position and the Knee_to_Com line is on top of the vertical cartesian line (angle theta_1-0). Position B is when the Knee_to_Com line is at 30 degrees from the vertical cartesian line (angle theta_2=30) Position C is when the Knee_to_Com line is at 60 degrees from the vertical cartesian line (angle theta_3-60) Position D is when the Knee_to_Com line is at 90 degrees from the vertical cartesian line (angle theta_4-90). Knee B Knee Knee Knee