The Skeletal System and Its Movements 19plane and divides the body into anterior and poste-
rior portions of equal mass. The cardinal horizontal
or transverse plane runs transversely through the
body such that it is perpendicular to the sagittal and
frontal planes. During upright standing the horizontal
plane is parallel to the floor. It divides the body into
superior and inferior portions of equal mass.
In addition to these cardinal planes, there can be
other sagittal, frontal, or horizontal planes that run
parallel to their cardinal counterpart but differ in
that they do not pass through the center of mass of
the body and do not divide the body in half by mass.
These other planes are helpful for describing many
functional movements in which different segments
of the body are moving in planes parallel to a given
cardinal plane. While some texts term these noncar-
dinal planes secondary planes (Smith, Weiss, and
Lehmkuhl, 1996) or segmental planes (Kreighbaum
and Barthels, 1996), for purposes of simplicity this
text includes cardinal and noncardinal planes within
the terms sagittal, frontal, and horizontal planes as
described in table 1.6.
Anatomical Axes and Associated Movements
When movement occurs in a plane, it is always occur-
ring around an axis that is perpendicular to this
plane. Hence, there are three imaginary anatomical
reference axes, each associated with one of the three
basic planes—sagittal, frontal, and horizontal—pre-
viously described. When one is describing motion
about these axes in their respective planes, move-
ment can be of the whole body or of a body segment.
Examples of such movements in the sagittal plane are
shown in figure 1.10. With whole body movement the
axis generally runs through the center of mass of the
body, as with a forward somersault (figure 1.10A), or
through a point of external support. Examples of a
point of external support are the hands on a paral-
lel bar during a swinging motion, the hands on the
floor in a walkover (figure 1.10B), and the feet on
the floor in the preparation phase of a jump. With
movement of body segments, the axis runs through
the joint, again in a direction perpendicular to the
plane in which the movement occurs. To picture
the relationship between an axis and the motion
it allows, imagine a pencil running through your
joint in the direction associated with that given axis.
Then try to imagine what type of movement it would
allow and in what plane this movement would occur
(table 1.7). Mediolateral axes for the wrist, elbow,
shoulder, hip, knee, and ankle joints are shown in
figure 1.10C that would allow movements at these
joints in a sagittal plane.- Mediolateral axis (frontal axis). A mediolateral
(ML) axis runs in a side-to-side direction in a frontal
plane, perpendicular to a sagittal plane and allowing
motion in a sagittal plane. An ML axis through the
FIGURE 1.9 The three cardinal planes of the body and
their axes.TABLE 1.6 Basic Anatomical Planes
Name Definition
Sagittal plane(s) A vertical plane dividing body into right and left portions
Median plane The midsagittal plane dividing the body into equal right and left portions
Frontal plane(s) A vertical plane dividing the body into front and back portions
Horizontal plane(s) A transverse plane dividing the body into upper and lower portions