The Skeletal System and Its Movements 25of the cone) while the other end stays stationary
(apex of the cone). For example, circumduction of
the shoulder occurs when you trace a circle with your
middle finger as seen in figure 1.15B.
- External rotation involves moving the anterior
surface of a limb outward or away from the midline of
the body. It is also termed lateral rotation or outward
rotation and is the primary motion used at the hip to
establish turnout. External rotation occurs in a horizon-
tal plane around a vertical (longitudinal) axis through
the body segment as seen in figure 1.16. The fact that
a longitudinal axis is involved is important for under-
standing rotation, as well as the difference between
rotation and circumduction. For rotation, both ends
of the segment stay at the same point in space and the
segment just twists along the long axis. For example,
rotation of the shoulder occurs when the entire arm is
twisted while the middle finger stays at the same place
rather than making a circle (circumduction), as shown
in figure 1.15A. In dance, external rotation of the hip
occurs during turning out from a parallel first position.
In contrast, circumduction of the hip is utilized when
FIGURE 1.14 Joint movements in the frontal plane about an anteroposterior (AP) axis: abduction-adduction and right
lateral flexion-left lateral flexion.
FIGURE 1.15 Distinguishing between shoulder rotation
and circumduction. (A) Rotation involves twisting along the
longitudinal axis of the limb with the middle finger rotating
in place, while (B) circumduction involves a cone-shaped
movement path with the middle finger tracing a circle.