In a closed-chain knee exercise, at what angle is the knee weakest?

In a closed-chain knee exercise, at what angle is the knee weakest?

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

Answer: (D)

In closed-chain knee exercises the amount of knee extension torque you can generate depends on the angle at which the knee is bent, because both the muscle’s length and its lever arm change with angle. The quadriceps act through the patella to extend the knee, and their effective force production is strongest in mid-range when the lever arm is favorable and the muscle length is near optimal for force. As you move toward about 90 degrees of knee flexion, the lever arm and the muscle’s length combine to produce less knee-extension torque, so the knee is weakest at this angle. This is why tasks like squats or leg presses feel hardest around roughly 90 degrees of flexion—the mechanical advantage is reduced there, even though the joint is under substantial load.

In closed-chain knee exercises the amount of knee extension torque you can generate depends on the angle at which the knee is bent, because both the muscle’s length and its lever arm change with angle. The quadriceps act through the patella to extend the knee, and their effective force production is strongest in mid-range when the lever arm is favorable and the muscle length is near optimal for force. As you move toward about 90 degrees of knee flexion, the lever arm and the muscle’s length combine to produce less knee-extension torque, so the knee is weakest at this angle. This is why tasks like squats or leg presses feel hardest around roughly 90 degrees of flexion—the mechanical advantage is reduced there, even though the joint is under substantial load.