Which statement best describes knee strength during an open-chain exercise?

Which statement best describes knee strength during an open-chain exercise?

• A. The Knee Is Strongest at 90 Degrees of Flexion
• B. The Knee Is Weakest at 0 Degrees of Flexion
• C. The Knee Is Strongest at 45 Degrees of Flexion
• D. The Knee Is Strongest at Full Extension

Answer: (A)

In open-chain knee actions, the torque you can generate at the knee depends on the quadriceps’ force and the moment arm about the knee joint. At about 90 degrees of knee flexion, the quadriceps tendon has a favorable moment arm and the muscle is near its optimal length for force production. This combination produces the greatest knee-extension torque for a given muscle activation, so the knee is strongest in this position during open-chain exercises. As the knee moves toward full extension, the moment arm shortens and the quadriceps may be less length-tension optimal, reducing torque. In shallower angles or deeper flexion beyond 90 degrees, the leverage or muscle length are less favorable, leading to lower knee-extension strength compared with the 90-degree position.

In open-chain knee actions, the torque you can generate at the knee depends on the quadriceps’ force and the moment arm about the knee joint. At about 90 degrees of knee flexion, the quadriceps tendon has a favorable moment arm and the muscle is near its optimal length for force production. This combination produces the greatest knee-extension torque for a given muscle activation, so the knee is strongest in this position during open-chain exercises. As the knee moves toward full extension, the moment arm shortens and the quadriceps may be less length-tension optimal, reducing torque. In shallower angles or deeper flexion beyond 90 degrees, the leverage or muscle length are less favorable, leading to lower knee-extension strength compared with the 90-degree position.