Flexion and extension occur in which anatomical plane?

• A. Frontal plane
• B. Transverse plane
• C. None of the above
• D. Sagittal plane

Answer: (D)

Flexion and extension take place in the sagittal plane, the vertical slice that splits the body into left and right sides. In this plane, joints move by bending forward or backward: flexion reduces the angle between two bones, while extension increases that angle back toward the normal position. For example, bending the elbow or knee is flexion, and straightening those joints is extension. The frontal plane handles movements to the side of the body (abduction/adduction), and the transverse plane handles rotational movements. So flexion and extension are best understood as movements occurring in the sagittal plane.