Which plane of movement is used for exercises that involve extension and flexion such as marching and knee lifts?

The sagittal plane is the correct answer because it divides the body into left and right halves and is the plane in which forward and backward movements occur. Exercises that involve extension and flexion, such as marching and knee lifts, primarily occur along this plane. When a person performs a knee lift, they are flexing at the knee joint to bring the leg upwards, and when they extend the leg back down, they are moving in the opposite direction—both of which occur in the sagittal plane.

In contrast, the coronal plane, which divides the body into front and back sections, is associated with movements that involve lateral (side-to-side) activities, such as jumping jacks. The transverse plane, on the other hand, divides the body into upper and lower sections and is where rotational movements occur, such as twisting exercises. The neutral plane isn't a recognized plane of movement in the same way as the other three; it's more often used to describe a position without movement. Therefore, the movements of extension and flexion specifically align with the characteristics of the sagittal plane.