Knee flexion is best described as:

• A. Straightening the knee
• B. Extending the hip
• C. Rotating the knee inward
• D. Bending the knee

Answer: (D)

Knee flexion means bending the knee, which decreases the angle between the thigh and the shin. It’s the action you use when you bring the heel toward the buttocks. The opposite motion is knee extension, which straightens the knee. Extending the hip moves the thigh at the hip joint, not the knee, and rotating the knee inward is a rotation of the leg that isn’t described by flexion. So bending the knee is the correct description.