Dance Anatomy & Kinesiology

(Marvins-Underground-K-12) #1

56 Dance Anatomy and Kinesiology


Muscles as Force Couples


The technical definition of a force couple is two
forces that are equal in magnitude and opposite in
direction and are located at a distance from the axis
such that they produce rotation. An example of a
force couple is the use of the hands on the steer-
ing wheel of an automobile to produce rotation of
the wheel as seen in figure 2.15A. In dance, a force
couple is formed by the feet to produce rotation of
the body for turns such as a pirouette. When refer-
ring to muscles in the body, “force couples” can be
more loosely used to describe muscles located at
different positions relative to a joint axis but that act
together to produce rotation in the same direction.
In such anatomical force couples, the lines of pull
of muscles are not necessarily directly opposite in
direction and equal in magnitude. Examples of force

couples used whenever the arms are raised overhead
are shown in figure 2.15B. The upper trapezius and
serratus anterior muscles as well as the upper trape-
zius and lower trapezius can work as force couples
to produce upward rotation of the scapula necessary
for raising the arms overhead (see Scapulohumeral
Rhythm on p. 397 for a more detailed discussion on
the function of these particular muscles).

Special Considerations
With Multijoint Muscles

Muscles can cross one or multiple joints, and the
number of joints crossed dramatically influences the
muscle’s contribution to movement. As their names

FIGURE 2.15 Force couples. (A) Hands on steering
wheel and (B) muscles of scapula (posterior view).

B


A


FIGURE 2.16 Number of joints crossed by muscles.
(A) Single-joint (posterolateral view), (B) two-joint (anterior
view), and (C) multijoint muscles (posterior view).
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