In an open-chain knee exercise, at what knee flexion angle is the knee strongest?

In an open-chain knee exercise, at what knee flexion angle is the knee strongest?

• A. 0 Degrees of Flexion
• B. 45 Degrees of Flexion
• C. 90 Degrees of Flexion
• D. 135 Degrees of Flexion

Answer: (C)

In open-chain knee extension, the amount of torque the quadriceps can produce depends on the lever arm of the extensor mechanism as the knee angle changes. As the knee moves from near full extension, the moment arm of the quadriceps increases, making the knee joint torque greatest when the pull of the quadriceps is nearly perpendicular to the knee’s axis. Around midrange, near ninety degrees of flexion, this lever arm is maximized, so you generate the most extensor torque. If you keep going toward deeper flexion, the lever arm shortens again due to knee geometry and patellofemoral contact, so the torque drops. At very small flexion, the muscle is short and the moment arm is less favorable, also reducing torque. So, the knee is strongest around ninety degrees of flexion in open-chain movements.

In open-chain knee extension, the amount of torque the quadriceps can produce depends on the lever arm of the extensor mechanism as the knee angle changes. As the knee moves from near full extension, the moment arm of the quadriceps increases, making the knee joint torque greatest when the pull of the quadriceps is nearly perpendicular to the knee’s axis. Around midrange, near ninety degrees of flexion, this lever arm is maximized, so you generate the most extensor torque. If you keep going toward deeper flexion, the lever arm shortens again due to knee geometry and patellofemoral contact, so the torque drops. At very small flexion, the muscle is short and the moment arm is less favorable, also reducing torque. So, the knee is strongest around ninety degrees of flexion in open-chain movements.