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Head and Neck Posture at Computer Workstations - What's Neutral? by Dennis Ankrum Proceedings of the 14
th
Triennial Congress of the International Ergonomics Association.
(2000, vol. 5, pp. 565-568).
HEAD AND NECK POSTURE AT COMPUTER
WORKSTATIONS WHATS NEUTRAL?

Dennis R. Ankrum
Human Factors Research, Nova Solutions, Inc., Effingham, Illinois USA
Kristie J. Nemeth
University of Dayton Research Institute, Dayton, Ohio USA

In a study of comfortable head/neck posture in the absence of a visual target for 24
seated subjects, mean head tilt (Ear-Eye Line) angle was 7.7� above horizontal, and mean
head/neck posture (C7-tragus against vertical) was 43.7�. Using these and other studies
findings as reference points for neutral, studies examining posture at different computer
monitor heights were reviewed: eye-level monitors resulted in head/neck extension.


INTRODUCTION

Viewing a VDT involves an interaction
between two systems: vision and posture. From a
visual system standpoint, lower monitor positions
have been shown to be beneficial in terms of
accommodation, convergence and reduced risk of
Dry Eye Syndrome when compared to those at eye
level (see Ankrum, 1997 for a review). The postural
tradeoffs can be evaluated by several methods,
including that of comparing observed postures to
neutral postures. A valid estimate of neutral neck
posture is critical to any such analysis.

Neck posture recommendations in the literature

Most studies measuring neck flexion/extension
have not defined the zero starting point. For
example, Chaffin (1971) has been cited as the basis
for the recommendation not to exceed 30� of flex-
ion over sustained periods. The RULA workstation
assessment method (McAtamney and Corlett, 1993)
considers neck flexion to be of progressively greater
risk over 10� and assigns the highest risk level to
any amount of extension. However, neither article
defines the zero point from which flexion/extension
was measured. Such a reference point would be
necessary in order to apply any recommendations.

Definition of Neutral


Several attempts have been made to define
neutral of the head/neck region, but most are
reference points rather than postures of least
musculoskeletal stress. The zero point (dividing

flexion from extension) has been variously
described as: the posture of the head/neck when
standing erect and looking at a visual target at eye
level; the posture of the head/neck when standing
erect and looking at a visual target 15� below eye
level; and normal erect posture.

Physiological landmarks in measuring head/neck
posture

Head tilt.
Several landmarks have been used in defining
head tilt (see Figure 1). The simplest metric can be
called head tilt angle. Head tilt angle definitions
have utilized angles defined by the true horizontal
Figure 1. Head posture landmarks and metrics. in conjunction with any of the following lines: the
tragus (the cartilaginous protrusion in front of the
ear hole) to the canthus (outer slit in the eyelid)
(known as the Ear-Eye Line); the tragus to the
bottom of the eye socket (Frankfurt Line); the
tragus to the nasion (the middle of the naso-frontal
suture); and the tragus to the infraorbital notch
(junction of the lateral 1/3 and medial 2/3 of the
inferior orbital rim). Still others have used X-rays to
measure the relationships between internal
structures, without reference to external landmarks.
The different metrics make it difficult to
compare results. Jampel and Shi (1992) estimated
that the Ear-Eye Line (E-E Line) is inclined by
10.82� from the Frankfurt Line, but no other
conversion rules have been published.

Head/neck angle.
The angles described above refer to only one
aspect of the complex geometry involved in
head/neck posture. Eight articulations can be
involved in flexion/extension they involve the
skull and C1 through T1 vertebrae. Some studies go
beyond simple head tilt angle and measure a more
complex posture that can be called head/neck
angle, often referred to as the degree of forward or
peering head posture, or neck protractio n. This is
typically defined as the angle between true vertical
(or sometimes horizontal) and a line connecting C7,
T1, or the acromion to various skull landmarks such
as those described above. The C7tragus angle is
also known as the cranio-vertebral angle.
To an extent, head tilt and head/neck angles are
independent. It is possible to observe postures that
combine a flexed head-neck angle with an extended
head angle (picture a bifocal wearer trying to read
small characters on an eye-level monitor). The
muscle loads of the two postures, particularly for
the dorsal muscles of the region, are almost
certainly quite different, so a more useful
description of head/neck posture in the sagittal
plane uses both measures: head tilt angle and
head/neck angle.

Ideal head-neck flexion and extension

Head tilt during erect posture.
Jampel and Shi (1992) found head tilt (E-E
Line) to be +15� when subjects assumed a head-
erect posture and stared straight ahead. Grey et al.
(1966; converted from Frankfurt Line results) found
a nearly identical +14.5� E-E Line when subjects sat
in their posture of greatest height. Hsaio and
Keyserling (1991) found a head tilt of +2�
(estimated from the study description) in normal
erect sitting.

Head tilt as affected by comfort or muscle
equilibrium.
Grey et al. (1966) found head tilt (E-E Line) to
be 0� when subjects sat in a self-defined most
comfortable posture without a backrest.
Studies of sleeping astronauts show head angle
in microgravity as 11-19� more flexed than in
normal gravity (Thornton, 1978). At least part of
this is believed to be due to spine straightening
under those conditions, but the amount of flexion is
still substantial.

Head tilt at computer workstations.
Sommerich et al. (1998) measured the E-E Line
in three monitor conditions: with the center of the
monitor at 0, 17.5 and 35� below horizontal eye
level. They found E-E Line angles of 25, 16 and 4�
respectively. Villanueva et al. (1996) found similar
results: viewing angles of 0, 10, 17.5, 27.5 and
38.5� resulted in E-E Line angles of 27.3, 22.9,
15.5, 11.5 and 4.7�. Turville, et al. (1998) found E-
E Line angles of 11.9 and 6.3� at viewing angles
of 15� and 40�, respectively (See figure 2).

Head/neck angle during erect posture.
Raine and Twomey (1997) found a head/neck
angle of 41.1� and Johnson (1988) found 40.6� with
Figure 2. Head tilt at computer workstations.
-10�
-5�
0�
5�
10�
15�
20�
25�
30�
Ear-Eye Line
Turville
Sommerich
Villanueva
15� Jampel & Shi (1992)
7.7� Most comfortable
0� Grey (1966)
0�
-10�
-15�
-17.5�
-27.5�
-35�
-38.5�
-40�
Viewing Angle
EXTENSION standing subjects who were asked to look straight
ahead. Head-neck angle was measured from the C7
to the tragus.

Head/neck angle at computer workstations.
In a study that included head/neck angle at
different monitor heights, Sommerich et al. (1998)
found C7-tragus angles of 36�, 38�, and 42�
corresponding to center-of-monitor heights of 0�,
17.5�, and 35� below eye height, respectively (See
figure 3).

CURRENT STUDY

To separate the effects of vision on posture, we
measured the self-defined most comfortable head
tilt and head/neck angles in the absence of a visual
target.

METHODS

Twenty-four college students were recruited as
part of a larger study on workstation configurations.
Subjects were 18-28 years old and had no history of
musculoskeletal disorders.
A marker was attached to C7 and the procedure
was videotaped. Subjects were seated in a chair
with a vertical backrest and were instructed to close
their eyes and slowly mo ve their heads, first from
side to side (abduction and adduction) and then
front to back (flexion and extension). They were
then asked to find the position they felt was most
comfortable. When the subjects announced they had
established their most comfortable position, the
experimenter marked the videotape. The exercise
took approximately 30 seconds.
Head tilt and head/neck angles were measured
using software that converted video images to data
files (Image-Pro
�
). Head tilt was defined as the
angle between the Ear-Eye Line and horizontal.
Head/neck posture was defined as the angle
between the vertical and a line running through C7
and the tragus.

RESULTS

The mean most comfortable head tilt (Ear-
Eye Line) was 7.7� [SD: 8.1] above the horizontal.
The mean most comfortable head/neck angle was
43.7� [SD: 6.9]. No significant gender differences
for head tilt or head/neck angle were found.
There was a significant negative correlation
between head tilt and neck angle [r= -0.389, p<.05].
Subjects with larger head/neck angles had smaller
head tilt angles.

DISCUSSION AND CONCLUSION

To separate the effects of vision on posture,
comfortable head ti