Dance Anatomy & Kinesiology

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).