Here's why:

* Sagittal plane: Divides the body into left and right halves. Movements in this plane are flexion/extension (like bending forward/backward) and dorsiflexion/plantarflexion (like pointing your toes up/down).

* Frontal plane: Divides the body into front and back halves. Movements in this plane are abduction/adduction (like moving your arms away/toward the midline) and lateral flexion (like bending your torso sideways).

* Oblique plane: Is a diagonal plane that intersects the sagittal and frontal planes at an angle. Movements in this plane combine elements of both planes, creating a diagonal or rotational motion.

Examples of movements in the oblique plane:

* Circumduction: A circular movement that combines flexion, extension, abduction, and adduction (like swinging your arm in a circle).

* Diagonal shoulder abduction: Raising your arm upward and outward at an angle, combining elements of abduction and flexion.

* Diagonal trunk rotation: Twisting your torso to the side while also bending forward or backward.

Important note: Many complex movements in everyday life and in sports involve movement in the oblique plane. This is because the human body rarely moves in a purely sagittal or frontal plane.