Planes and axes of motion
Human motion is complex. We confront this complexity by analyzing movement in a definite sequence:
Depending on the joint, we must analyze the motion at just ONE, or TWO, but never more than THREE PLANES.
- We name the joints at which movement occurs
- We describe the motion at ONE JOINT AT A TIME.
- At each joint, we describe the motion in ONE PLANE AT A TIME
Your text illustrates the three planes on a body in anatomic position on page 3. Disregard their use of x, y, and z orientations.
- Frontal (sometimes called the coronal plane)
- Transverse (sometimes called the horizontal plane)
Another view of the cardinal planes
When we describe motion, we mentally move the plane so that it "cuts through" the joint at or near the joint surface. Imagining a plane which cuts through at the level of a joint permits us to draw a two-dimensional (or planar picture of the joint:
Each plane is oriented in relation to the body, not to the "world." In other words, when the body or any of its segments change position, the planes change their orientation along with them.
EACH PLANE IS DEFINED BY AN AXIS
Each plane is defined by an axis, a line that is perpendicular to the plane. When we observe a drawing of the joint in a single plane, we appreciate the joint's axis as a point; in the drawings linked above, an 'x' marks the joint axis.
Smith, L.K., Weiss, E.L. & Lehmkuhl, L.D. (1996). Brunnstrom's clinical kinesiology (5th ed.). Philadelphia: F.A. Davis.