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Touch-screen tablet user configurations and case-supported tilt affect head and neck flexion angles

Authors:
  • Brooks Running

Abstract and Figures

The aim of this study was to determine how head and neck postures vary when using two media tablet (slate) computers in four common user configurations. Fifteen experienced media tablet users completed a set of simulated tasks with two media tablets in four typical user configurations. The four configurations were: on the lap and held with the user's hands, on the lap and in a case, on a table and in a case, and on a table and in a case set at a high angle for watching movies. An infra-red LED marker based motion analysis system measured head/neck postures. Head and neck flexion significantly varied across the four configurations and across the two tablets tested. Head and neck flexion angles during tablet use were greater, in general, than angles previously reported for desktop and notebook computing. Postural differences between tablets were driven by case designs, which provided significantly different tilt angles, while postural differences between configurations were driven by gaze and viewing angles. Head and neck posture during tablet computing can be improved by placing the tablet higher to avoid low gaze angles (i.e. on a table rather than on the lap) and through the use of a case that provides optimal viewing angles.
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Work 41 (2012) 81–91 81
DOI 10.3233/WOR-2012-1337
IOS Press
Touch-screen tablet user congurations and
case-supported tilt affect head and neck
exion angles
Justin G. Younga, Matthieu Trudeaua, Dan Odellb, Kim Marinelliband Jack T. Dennerleina,c,
aDepartment of Environmental Health, Harvard School of Public Health, Boston, MA, USA
bMicrosoft Corporation, Richmond, WA, USA
cDepartment of Orthopaedic Surgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
Received 29 November 2011
Abstract.Objective: The aim of this study was to determine how head and neck postures vary when using two media tablet
(slate) computers in four common user congurations.
Methods: Fifteen experienced media tablet users completed a set of simulated tasks with two media tablets in four typical user
congurations. The four congurations were: on the lap and held with the user’s hands, on the lap and in a case, on a table and
in a case, and on a table and in a case set at a high angle for watching movies. An infra-red LED marker based motion analysis
system measured head/neck postures.
Results: Head and neck exion signicantly varied across the four congurations and across the two tablets tested. Head and neck
exion angles during tablet use were greater, in general, than angles previously reported for desktop and notebook computing.
Postural differences between tablets were driven by case designs, which provided signicantly different tilt angles, while postural
differences between congurations were driven by gaze and viewing angles.
Conclusion: Head and neck posture during tablet computing can be improved by placing the tablet higher to avoid low gaze
angles (i.e. on a table rather than on the lap) and through the use of a case that provides optimal viewing angles.
Keywords: Slate computing, media tablets, mobile computing
1. Introduction
Slate, tablet, or media tablet computers (e.g. the Ap-
ple iPad ) have recently become ubiquitous portable
and mobile computing devices. In 2010, it is estimated
that 17.6 million tablets were sold and that number is
expected to increase more than three-fold in 2011 [1].
Market projections predict that there could be more
than 300 million tablets sold worldwide in 2015, with
more than 80 million tablet users in the US alone [1,2].
Corresponding author: Jack T. Dennerlein, Harvard School of
Public Health, 665 Huntington Avenue, Boston, MA 02115, USA.
Tel.: +1 617 384 8812; Fax: +1 617 384 8767; E-mail: jax@hsph.
harvard.edu.
Tablet computers provide a new combination of high
portability and simple user interfaces through integrat-
ed touch-displays which may illicit usage behavior
unique to its form factor. In addition, the sudden pop-
ularity and adoption of the media tablet has not al-
lowed for typical physical ergonomics parameters such
as posture or muscular effort during use to be assessed.
As such, no design or usage guidelines similar to those
developed for current desktop and notebook (laptop)
computers (e.g. ISO-9241, ANSI/HFES 100 (USA),
and CSA-Z412-M89 (Canada)) exist. Hence, there is
an imminent need for evaluation of tablets while in their
early stage of acceptance in order to build a set of rec-
ommended guidelines to optimize system performance
and users’ well-being.
1051-9815/12/$27.50 2012 – IOS Press and the authors. All rights reserved
82 J.G. Young et al. / Touch-screen tablet user congurations and case-supported tilt affect head and neck exion angles
Tab le 1
Mean (SD) participant anthropometry
Age Height (cm) Weight (lbs) Hand length (mm)
Males (n=7) 29 ±4 177 ±9 83.5 ±7.3 193 ±11
Females (n=8) 30 ±6 170 ±6 65.3 ±5.9 176 ±8
ALL (n=15) 29 ±5 174 ±8 73.5 ±11.3 184 ±13
A major difference between tablet and desktop or
notebook computers is that tablets functionally inte-
grate the display and the user input via a touch-screen.
This results in the devices being highly portable with
many potential display positions and locations during
use. Because computer work has been and continues to
be associated with discomfort and pain in the neck and
shoulders [3–8], many studies have investigated how
display/monitor positioning affects neck and shoulder
posture and muscle activity [9–11]. Higher display lo-
cations lead to decreased head and neck exion that
approach more neutral postures; while lower gazes lead
to increasingly exed postures which are associated
with an increase in neck extensor activity [10,12,13].
Biomechanical models of the neck musculature show
that excessive head exion leads to large muscle loads
and strains [14]. As a result, it is generally hypoth-
esized that very low monitor positions may put users
at risk of developing neck and shoulder discomfort or
musculoskeletal disorders.
In preliminary observational studies of tablet com-
puter users, several different support and grip cong-
urations were adopted, ranging from holding the de-
vice in the hands, lifting and supporting it with a fore-
arm, placing it in the lap, or using a case to rest the
device at a set angle on a table. Placement in the lap
suggests the display may be positioned quite low and
similar to notebook computers; though the screen tilt
cannot be adjusted independently of the keyboard input
like with a notebook. As a result, it is unclear what
specic postures users assume while interacting with
these devices. Therefore, it is the aim of this research
study to investigate head and neck posture for various
usage congurations commonly observed during typi-
cal tablet computer use and how head and neck posture
varies with different tablets and their case designs with
different tilt angle settings.
2. Methods
To address the study aim, a laboratory-based repeat-
ed measures experiment was completed which tested
the hypothesis that tablet/case design and user cong-
uration affects head and neck posture. Head and neck
postures were measured while fteen adult experienced
tablet computer users (Table 1) completed a set of sim-
ulated tasks on two mediatablet computers in four con-
gurations representative of typical observed use. All
participants either owned or had experience working
with a tablet computer and reported no current or pre-
vious history of head, neck, back or upper extremity
MSDs. Each participant gave informed consent prior
to beginning the study. The Harvard School of Pub-
lic Health Ofce of Human Research Administration
approved all protocols and consent forms.
In order to represent typical user situations, partici-
pants performed all the tasks while seated in a lounge-
type chair with a seat pan height of 44 cm, a slightly
reclined backrest, and no armrests (Fig. 1). In addition,
a 40 cm tall ottoman-style footrest was provided as an
optional accessory. Though not required to use the ot-
toman, subjects were free to use it if desired except for
conditions when the tablet was on the table. The goal
was to have the subject sit in a comfortable position
that would be similar to how they would use their own
tablet at home or travelling. All nearby light sources in
the laboratory were indirect lighting and the chair was
positioned to minimize any glare on the tablet screens.
2.1. Independent variables: Tablet and conguration
The two media tablet computers tested were Tablet 1,
an iPad2 (Apple, Cupertino, CA, USA) with dimen-
sions of 241.2 ×185.7 ×8.8 mm and mass 601 g, and
Tablet 2, a Xoom (Motorola Mobility, Libertyville, IL,
USA) with dimensions of 249.1 ×167.8 ×12.9 mm
and 708 g. Tablet 1 ran on the iOS 4.3 operating sys-
tem (Apple, Cupertino, CA, USA) and Tablet 2 ran on
the Android 3.0 operating system (Google, Mountain
View, CA, USA). Each device was tested only in the
landscape orientation. Each tablet also had a propri-
etary case that could be tted to the device and ad-
justed in order to prop up or tilt the tablet computer
(Fig. 1b, c, d). Only a few different tilt angles are
possible with each case and each case’s tilt angles are
different: Case 1, the Smart Cover (Apple, Cupertino,
CA, USA) allows for tilt angles (from horizontal) of
15and 73, and Case 2, the Portfolio Case (Motorola
Mobility, Libertyville, IL, USA) allows for tilt angles
J.G. Young et al. / Touch-screen tablet user congurations and case-supported tilt affect head and neck exion angles 83
Fig. 1. Example of subject in four usage congurations. (a) Tablet 2 on the lap without its case held by the subject’s hand (Lap-Hand) (b) Tablet
1 on the lap in its case set to its lower angle (Lap-Case). (c) Tablet 2 on the table in its case set to its lower angle (Table-Case). (d) Tablet 1 on
the table in its case set to the higher angle for watching movies (Tablet-Movie).
of 45and 63(Fig. 2). The order of testing the tablets
were randomized and balanced across subjects.
Four user congurations, which consisted generally
of a location (on the lap or table) and a support condition
(hand-held or in a case), were tested (Fig. 1). The
four congurations (Lap-Hand, Lap-Case, Table-Case,
and Table-Movie) were chosen based on unpublished
observations of adult media tablet computer users in
their own homes and in usability studies. The order
of the congurations were randomized and balanced
within each tablet.
For the Lap-Hand conguration (Fig. 1a), the tablet
was supported by placing it on the lap (top of the thighs)
while one or two hands held and adjusted the tablet tilt.
This conguration was actually two conditions, the rst
where only one hand held and adjusted the tablet tilt
while the other hand interacted with the screen, and the
second where both hands held and adjusted the tablet
tilt while only the thumbs interacted with the screen.
Since there were no statistically signicant differences
in dependent variables between these two specichand-
held conditions, the results were averaged together into
the single Lap-Hand conguration. No cases were used
with the tablets for the hand-held conditions. The spe-
cic position on the lap and the tilt angle were chosen
by the participants; they were instructed only to place
and hold the tablet in a comfortable position.
For the Lap-Case (Fig. 1b) and Table-Case (Fig. 1c)
congurations, the tablets were inserted into their re-
spective cases and set to the lower of the two angle
settings (15for Tablet 1 and 45for Tablet 2, see
Fig. 2). Similar to the Lap-Hand conguration, par-
ticipants were free to set the tablets in their cases on
their laps in a comfortable position. For the Table-Case
conguration, the tablets were placed in their cases on
a 66.7 cm high table. Participants were instructed to
position the tablet directly in front of them and at a
comfortable distance.
For the Table-Movie conguration, the tablets were
inserted into their cases and set to the higher of the two
84 J.G. Young et al. / Touch-screen tablet user congurations and case-supported tilt affect head and neck exion angles
Fig. 2. Two tested media tablets and cases. Figures are to scale for proper comparison. Each tablet has a case that allows for two screen tilt angles:
15and 73for Tablet 1 (top) and 45and 63for Tablet 2 (bottom). All trials were completed with the Tablets in the landscape orientation as
shown.
angle settings (73for Table 1 and 63for Tablet 2,
see Fig. 2). Participants were instructed to position the
tablet on the table directly in front of them at a distance
comfortable for viewing a movie assuming minimal
touch interaction would be required.
2.2. Software tasks
During the experiment, participants completed sim-
ulated computer tasks representative of typical tablet
usage: Internet browsing and reading, game playing, e-
mail reading and responding, and movie watching. The
ve-minute Internet browsing and reading task con-
sisted of entering URL addresses, navigating through
4 pages, and reading a newspaper article. The three-
minute gaming task consisted of playing the common
solitaire card game available on most computers. The
three-minute e-mail reading and responding task con-
sisted of using the tablet-based email client to read and
respond to short email messages in an email account
set up by the experimenters. Subjects read messages
and responded with short replies answering the simple
question in the read message (e.g. “What is your fa-
vorite food and why?”). The ve-minute movie watch-
ing task consisted of watching one of three pre-selected
online streaming videos. While the two tablets differed
in their operating system software, tasks were selected
and designed to have similar interface requirements.
Not all tasks were completed in each conguration
(Table 2). For the Lap-Hand conguration, partici-
pants performed the Internet browsing and reading task
and the game playing task only. For the Lap-Case and
Table-Case congurations, participants performed the
Internet browsing and reading task and the e-mail read-
ing and responding task only. For the Table-Movie con-
guration, participants performed the movie watching
task only. There was a short break (approximately two
minutes) between tasks.
2.3. Dependent variables and instrumentation
The primary biomechanical outcomes were head and
neck postures represented by three angles: head ex-
ion, neck exion, and cranio-cervical angle (Fig. 3). In
addition to these postures and due to their interaction
with head and neck postures [11] secondary outcomes
included the position of the center of the tablet’s screen
relative to the eyes (gaze angle and gaze distance) and
C7 spinal process (horizontal and vertical position) as
well as the orientation of the tablet with respect to the
global horizontal (tilt angle) and the direction of gaze
(viewing angle). Because the tablet was placed directly
in front of the subject, the rotation or lateral tilt of the
head and neck was not of interest.
These angles and positions were calculated from 3-
dimensional kinematics of the head and trunk measured
using an infrared three-dimensional motion analysis
system (OptotrakCertus, Northern Digital, Waterloo,
Canada). Two clusters of three infrared light emitting
diodes (IREDs) xed to a rigid surface were secured
to the head and trunk [15,16]. An additional cluster of
4 IREDs was attached to the upper right corner of the
tablet computer. The 3-D position of these IREDs were
tracked at 100 Hz and recorded to a personal computer
and then digitally ltered through a low-pass, fourth-
order Butterworth lter with a 5 Hz cutoff frequency.
J.G. Young et al. / Touch-screen tablet user congurations and case-supported tilt affect head and neck exion angles 85
Tab le 2
Four user congurations tested
Conguration Location of tablet Tablet support/basis of tilt Software tasks performed
Lap-Hand Subject’s lap One or both hands/self-selected tilt Internet browsing and reading,
Game playing
Lap-Case Subject’s lap Case/lower case tilt setting Internet browsing and reading,
E-mail reading and responding
Table-Case Table surface Case/lower case tilt setting Internet browsing and reading,
E-mail reading and responding
Table-Movie Table surface Case/higher case tilt setting Movie watching
Fig. 3. Dependent variables. Head and neck exion angles and the
cranio-cervical angle along with the position and orientation of the
media tablet computer relative to both C7 and relative to the eyes.
Head exion angle is the angle between global vertical and the vector
pointing from OC1 to Cyclops. Neck exion angle is the angle
between global vertical and the vector pointing from C7 to OC1. The
cranio-cervical angle is the angle between the vector pointing from
OC1 to Cyclops and the vector pointing from O C1 to C7. Tablet tilt is
respect to horizontal. Viewing angle is the angle between the screen
surface and the gaze vector. The horizontal and vertical position of
the tablet (not shown) is relative to C7.
Using the system’s digitizing probe, the locations of
the bilateral outer canthi (head cluster), bilateral trag-
ic (head cluster), and C7 spinal process (trunk clus-
ter) boney landmarks and the four corners of the tablet
(tablet cluster) were digitized relative to their associat-
ed IRED cluster. In order to calculate dependent vari-
ables, three additional 3-D locations were specied:
the midpoint between the left and right outer canthi
(‘Cyclops’), midpoint between the left and right tragi
(representing the occiput-cervical joint ‘OC1’), and the
center of the tablet screen (Fig. 3). For the duration
of the measurements, the 3-D position and orientation
of these landmarks were calculated based on the po-
sition and orientation of their associated IRED clus-
ter [17]. Angles were then derived from these segment
and landmark positions and orientations as depicted in
Fig. 3. Mean values for continuous measures of the
three head/neck angles and 6 position and orientation
parameters of the tablet computer were calculated as
outcome metrics for each experimental condition (over
all tasks performed in that condition).
2.4. Statistical analysis
To test the hypothesis that head and neck postures
varied across tablets and user congurations, we em-
ployed a 2 ×4 repeated measures analysis of variance
(RMANOVA) for each of the 3 head and neck postures
along with the 6 tablet position and orientation met-
rics with tablet (Tablet 1/Tablet 2) and conguration
(Lap-Hand/ Lap-Case/Table-Case/Table-Movie) set as
xed effects and participant as a random effect. The
tablet-conguration interaction term was also includ-
ed. When signicance was observed for an effect (p<
0.05), a post-hoc Tukey’s HSD test was used to deter-
mine if differences in the metricsexisted between com-
parisons. All analyses were run using JMP Software
(SAS Institute, Cary, NC).
3. Results
Head and neck exion postures varied signicantly
between the two media tablet devices, with Tablet 1
associated with the more exed postures (Table 3). The
postures also varied signicantly between the four us-
er congurations with the head and neck exion being
signicantly reduced during the Table-Movie cong-
uration (Table 3). For the other three congurations
head and neck exion was quite large, 15 to 25 degrees
beyond values associated with “neutral” head and neck
postures reported in previous studies [18–24]. The
variation across the congurations differed between the
two tablets as indicated by a signicant interaction term
(Fig. 4). Tablet 1 had more exed postures when the
case was in use. The head neck postures were similar
between the two tablets when they were tilted by hand
(Lap-Hand) or in the higher case angle position for
movie watching (Table-Case). Cranio-cervical angle
86 J.G. Young et al. / Touch-screen tablet user congurations and case-supported tilt affect head and neck exion angles
Fig. 4. Head and neck postures angles. Across subject average mean angles for each conguration and tablet are presented. Error bars represent
+/one standard error. The p-value is for the Tablet x Conguration interaction term in the ANOVA model. * indicates post-hoc signicant
differences within a conguration across the two tablets. The neutral postures are ranges reported in the literature (none found for the adult
cranio-cervical angle). Head posture signicantly varied across the scenarios and in different ways for the two tablets as indicated by the
signicant interaction terms (except for the cranio-cervical angle).
varied in a slightly differentfashion as the only signi-
cant difference was associated with the location of the
tablet (on the lap or on the table), with greater angles
for the lap congurations than the table congurations.
Gaze angle varied signicantly between the two
tablets with steeper gaze angles for Tablet 1 (Table 3).
The position of the center of the media tablets’ screen
varied signicantly across the four congurations with
the Table-Movie conguration having the greatest gaze
distance and vertical and horizontal position. Except
for gaze distance, the variation across the congura-
tions differed between the two tablets (Fig. 5), with
signicant differences between the two tablets for the
Lap-Case and Table-Case congurations. The varia-
tions in gaze angle were similar but inverse to those
observed in the head-exion angle. When using the
case, gaze angle was lower for Tablet 1 compared to the
Lap-Hand congurations. For Tablet 2 the gaze angles
were lowest for the Lap-Hand congurations.
The tablet tilt angle and the viewing angle varied sig-
nicantly between the two media tablet devices, with
Tablet 1 having on average 11 degrees more shallow tilt
angle and 8 degree more oblique viewing angle com-
pared to the Tablet 2 (Table 3). Again, the tilt angle
and view angle variations across the congurations dif-
fered between the two tablets as indicated by the sig-
nicant interaction term (Fig. 6). For the three cong-
urations where the tablets were in their cases, signif-
icant differences in tilt angle between the two tablets
correspond to differences in their case-specied tilt set-
tings (see Fig. 2). While viewing angles were consis-
tently near perpendicular across thefour congurations
for Tablet 2, signicantly lower viewing angles were
observed for Tablet 1 in the Lap-Case and Table-Case
congurations.
J.G. Young et al. / Touch-screen tablet user congurations and case-supported tilt affect head and neck exion angles 87
Tab le 3
Least square’s means (SE) for ANOVA main effects Tablet and Conguration
Tab le t Con guration
ANOVA1,2Tablet 1 Tablet 2 ANOVA1,2Lap-Hand Lap-Case Table-Case Table-Movie
Head/Neck Posture
Head Flexion ()p=0.0049 98 (2)A95 (2)Bp<0.0001 100 (2)A102 (2)A99 (2)A85 (2)B
Neck Flexion ()p=0.0002 50 (2)A47 (2)Bp<0.0001 49 (2)B52 (2)A54 (2)A40 (2)C
Cranio-Cervical ()p=0.6921 132 (2) 132 (2) p<0.0001 129 (2)B130 (2)B135 (2)A135 (2)A
Tablet Position relative to the Eyes
Gaze Angle ()p<0.0001 46 (1)B42 (1)Ap<0.0001 50 (1)C51 (1)C46 (1)B27 (1)A
Gaze Distance (cm) p=0.0132 53 (1)B55 (1)Ap<0.0001 50 (1)B,C 52 (1)B49 (1)C64 (1)A
Tablet Position relative to C7
Vertical (cm) p=0.0195 27 (1)B26 (1)Ap<0.0001 29 (1)C32 (1)D27 (1)B17 (1)A
Horizontal (cm) p=0.0003 54 (1)B57 (1)Ap<0.0001 49 (1)B50 (1)B51 (1)B72 (1)A
Tablet Orientation relative to Horizontal and the Eyes
Tilt Angle ()p<0.0001 35 (1)B46 (1)Ap<0.0001 36 (1)B29 (1)C30 (1)C67 (1)A
Viewing Angle ()p<0.0001 80 (2)B88 (2)Ap<0.0001 86 (2)B81 (2)C76 (2)D95 (2)A
1Repeated Measures ANOVA with subject as a random variable, Conguration and Tablet as xed effects. The model did include interaction
terms, which are reported in the Figs 4–6.
2For each dependent variables, values with the same superscript letters indicate no signicant difference and groupings are ranked such that
A>B>C>D.
Fig. 5. Tablet position relative to the eyes (Gaze Angle and Distance) and C7 (Horizontal and Vertical Position). Across subject average
mean-values for each conguration and tablet are presented. Error bars represent +/one standard error. The p-value is from the Tablet x
Conguration interaction term in the ANOVA model. * indicates post-hoc signicant differences within a conguration across the two tablets.
The gaze angle and position relative to C7 signicantly varied across the conguration and in different ways for the two tablets as indicated by
the signicant interaction term, with differences between the tables occurring for the Lap-Case and Table-Case congurations and no differences
observed for the Lap-Hand conguration. The Gaze Angle follows an inverse but similar pattern to head exion angle (Fig. 4).
88 J.G. Young et al. / Touch-screen tablet user congurations and case-supported tilt affect head and neck exion angles
Fig. 6. Tablet orientation. Across subject average mean angles for each conguration and tablet are presented. Error bars represent +/- one
standard error. The p-value is from the Tablet x Conguration interaction term in the ANOVA model. * indicates post-hoc signicant differences
within a conguration across the two tablets. The tilt and viewing angle of the tablets signicantly varied across the conguration and in different
ways for the two tablets as indicated by the signicant interaction term, with differences between the tables occurring for the Lap-Case and
Table-Case congurations and no differences observed for the Lap-Hand conguration. The viewing angle for Tablet 2 is relatively constant and
near perpendicular over the congurations.
4. Discussion
The goal of this study was to assess head and neck
posture during touch-screen tablet computer use for
several typical usage congurations on two different
tablet computers and their respective case designs. The
results indicate that both Tablet and Conguration af-
fect head and neck postures and that the effects across
congurations varied between the two tablets. Overall,
the observed head and neck exion angles are far from
neutral angles reported in the literature. Only for the
Table-Movie condition, where the device was set in its
steepest case angle setting and at the greatest horizontal
and vertical position, did posture approach neutral.
Differences in head and neck angles between the
two tablets appear to be driven by differences in case
design, which drastically altered the tablet tilt angle
and corresponding viewing angle (Fig. 6). Post hoc
results indicate that there were no differences between
tablets in the hand-held condition for any dependent
variable. When the devices were placed in their cases,
signicant differences between tablets existed for the
Lap-Case and Table-Case congurations (Figs 4, 5, 6).
Since the device proles were similar in terms of height,
width, and depth along with the accessible viewing
area (Fig. 2), the signicant main effect of Tablet in
the overall analysis must be due to differences in each
tablet’s case, specically the tilt angle.
For both tablets, the gaze angle changed in a simi-
lar fashion to the head exion angle across congura-
tions (Figs 4 and 5). Differences in head exion across
congurations appear to be driven largely by the gaze
angle associated with the vertical and horizontal po-
sition of the tablet screen’s center relative to the eyes
(see Fig. 3). Differences in head exion between the
two tablets (which can be attributed to case tilt) may
therefore be explained in part by how each case affects
the location of the center of the tablet screen. The shal-
lower tilt angle of Tablet 1’s case reduces the height
of the tablet which should theoretically increase the
gaze angle compared to Tablet 2’s in the Lap and Table
locations.
Our observed correlation between gaze angle and
head exion is similar to that reported in the review by
Straker et al. [11], where the authors compared head
exion versus gaze angle from numerous studies and
found a generally linear relationship. While our high
head exion and low gaze angles lay at the extreme
end of the spectrum of studies included in the review,
our results are similar to those reported in studies in-
vestigating notebook and sub-notebook computers [23,
25,26]. The largest previously reported head and neck
exion angles have been observed for writing on pieces
of paper or tablet pc’s with a stylus that are lying at
on a tablet surface [11,27,28] where, similar to a media
tablet, the input and the display are combined. Tilt-
ing the tablet/writing surface up from horizontal can
reduce head/neck exion for writing or touch-screen
tasks [29–31]. This suggeststhat shallower viewing an-
gles (non-perpendicular) may cause users to increased
head/neck exion, as our results show.
When in the Lap-Hand conguration, where users
can control the tablet tilt angle, subjects selected an
average tilt angle of approximately 36. This tilt angle
corresponded to a nearly perpendicular viewing angle
(mean =86). Preferred tilt angle for other congu-
J.G. Young et al. / Touch-screen tablet user congurations and case-supported tilt affect head and neck exion angles 89
rations in unknown, though Albin and McLoon (2007)
reported that most users nd a tablet tilt angle of 45
most acceptable for table top use. For Tablet 2, view-
ing angle remained relatively perpendicular and con-
stant across the other congurations, despite changes in
tablet location and tilt angle as set by the case (45for
Lap-Case and Table-Case). Preferred tilt angle most
likely changes depending on location of the tablet/gaze
angle and corresponds to tilt angles that allows for near
perpendicular viewing angles, which optimizes lumi-
nance and reduces perspective distortion of the dis-
play. Viewing angle has rarely been reported as a de-
pendent variable for previous studies but can be calcu-
lated if screen tilt angle and gaze angle are reported.
Self-selected viewing angles were 92–94for notebook
computers [25] and 91–99for desktop computers [32,
33], which are slightly greater than in the currentstudy.
This could be due to the need to interact with the hands
rather than just passively viewing information.
Cranio-cervical angle appears to be inuenced main-
ly by the vertical position of the tablet, with the on-
ly signicant difference occurring across the lap and
table locations but not within. Cranio-cervical angle
is a composite of head and neck exion angles, and
therefore in order to stay constant within Lap or Ta-
ble congurations any change in neck exion requires
an equal change in head exion. This suggests that
the postural responses to tablet usage conguration
are representative of complex changes in the cervical
spine/musculature [20].
In comparison to previous studies of head and neck
posture during computing,head and neck exion angles
were greater and cranio-cervical angles smaller, in gen-
eral, during tablet use than for desktop computing [11]
and for notebook computing [15,34,35]. Hence there
may be more of a concern for the development of neck
and shoulder discomfort during tablet use than for oth-
er computing form factors. Although specic evidence
linking computer display position and MSD outcomes
is limited and conicting [36–40], no studies have ex-
amined health outcomes when users exhibit the highly
exed head and neck postures observed for tablets in
the current study. A recent study [14] employing a so-
phisticated model of neck musculature concluded that
display positions that are associated with gaze angles
below 45are not recommended due to signicantly
increased strain on neck extensors. Therefore, media
tablet users may be at high risk to develop neck dis-
comfort based on current behaviors and tablet designs.
Of course, risk is a combination of posture, duration,
and frequency of exposure [41], and usage guidelines
should consider how these factors vary between high-
ly portable media tablets and that of traditional com-
puting scenarios. Our results suggest that continuous
use of tablets for longer durations should incorporate
placement of the device on higher surfaces and with
steeper case angle settings. However, these steeper tilt
angles may be detrimental for continuous input with the
hands. Further studies examining the effects of tablet
and conguration on arm and wrist postures are needed
to clarify and complete the postural evaluation.
These results need to be considered within the con-
text of the limitations of the study. This is a laboratory
study with simulated tasks and a large amount of in-
strumentation attached to the users. As a result users
may have altered their behavior from how the otherwise
naturally interact with tablets. The measurements for
each experimental condition were collected for only a
short period of time, which may allow users to adopt a
posture that they would not have been able to maintain
for a longer period of time. Another limitation is that
the two tablets selected for this study have very similar
physical dimensions. There were no signicant differ-
ences observed between tablets in the Lap-Hand (no
cases) conguration, but it is likely that differences in
posture may have been observed for tablets that were
more dissimilar. The broad range of media tablet com-
puter sizes currently available to consumers warrants
further assessment. This paper does not address the
posture of the arms, wrists, and hands, which, due to
potential conicts between visual access and tactile in-
put, may have inuenced on head and neck posture for
certain congurations or software tasks.
5. Conclusions
The use of media tablet computers is associated with
high head and neck exion postures, especially com-
pared to those for typical desktop computing scenarios.
These postures are affected by the type of case used
to support the tablets as well as the location of the de-
vice (e.g. lap vs table). These data suggest that head
and neck posture can be improved through case designs
that allow for optimal viewing angles and elevating the
device and avoiding lap-level locations.
These data are valuable for manufacturers to design
future products that promote more neutral postures and
increase the comfort of users. Results from these stud-
ies will be useful for updating ergonomic computing
standards and guidelines, which are imminently needed
as companies and health care providers weigh options
to implement wide-scale adoption of tablet computers
for business operations.
90 J.G. Young et al. / Touch-screen tablet user congurations and case-supported tilt affect head and neck exion angles
Acknowledgments
This study was funded in part by NIOSH R01
OH008373, the National Science Foundation grant
0964220, and a gift from the Microsoft Corporation.
The authors would also like to thank Tawan Udta-
madilok for her help with data collection.
Conictofintereststatement
Authors Kim Marinelli and Dan Odell are employees
of Microsoft, a partial funding source for this study. Dr.
Odell and Mrs. Marinelli took part in the experimental
and study design, including the selection of specic
usage congurations; however, they did not participate
in data collection or analysis and interpretation of the
results. There is no other potential conict of interest
or the appearance of a conict of interest with regards
to the study.
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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.
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Figure A.1 Walking Trial—Marker Locations and Mass and Frame Rate Information Table A.1 Raw Coordinate Data (cm) Table A.2(a) Filtered Marker Kinematics—Rib Cage and Greater Trochanter (Hip) Table A.2(b) Filtered Marker Kinematics—Femoral Lateral Epicondyle (Knee) and Head of Fibula Table A.2(c) Filtered Marker Kinematics—Lateral Malleolus (Ankle) and Heel Table A.2(d) Filtered Marker Kinematics—Fifth Metatarsal and Toe Table A.3(a) Linear and Angular Kinematics—Foot Table A.3(b) Linear and Angular Kinematics—Leg Table A.3(c) Linear and Angular Kinematics—Thigh Table A.3(d) Linear and Angular Kinematics—½ HAT Table A.4 Relative Joint Angular Kinematics—Ankle, Knee, and Hip Table A.5(a) Reaction Forces and Moments of Force—Ankle and Knee Table A.5(b) Reaction Forces and Moments of Force—Hip Table A.6 Segment Potential, Kinetic, and Total Energies—Foot, Leg, Thigh, and ½ HAT Table A.7 Power Generation/Absorption and Transfer—Ankle, Knee, and Hip
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Neck/shoulder pain is a common complaint, with evidence suggesting rates in adolescence have increased in line with increased computer use. The study aimed to examine the influence of gender on relationships between computer use, habitual posture and neck/shoulder pain. Adolescents (n = 1483) participating in the 14 year follow-up of the Raine Study cohort were surveyed for computer use, habitual sitting posture and neck/shoulder pain. Females used computers less than males (52% vs. 45% used for up to 7 h per week). Females sat much more upright than males with greater anterior pelvic tilt (9.4° vs. 0.4°). Females reported a higher 1 month prevalence of neck/shoulder pain (34.7%) than males (23.1%). A multivariate model showed neck/shoulder pain risk was increased in females (OR 2.61, 95% CI 1.70–4.00) and with computer use (OR 1.19, CI 1.01–1.40). Computer use is related to neck/shoulder pain and posture in adolescents but this relationship is different in boys and girls.Statement of Relevance: This study showed the confounding effect of gender on the relationships among computer use, posture and neck/shoulder pain and thus the need to consider genders separately in research and practice aiming to optimise young people's use of computers.
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This study took a comprehensive approach to evaluating effects of using a notebook computer stand-alone or along with inexpensive peripheral input devices. The study examined effects on biomechanics, productivity, and discomfort, and considered the impact of both computer configuration and task performed. It was hypothesized that, in general, the stand-alone configuration would induce greater postural fixity and more non-neutral postures than configurations with peripheral input devices. Dependent measures included muscle activity, posture and posture variation/fixity, productivity, and subjective assessments of discomfort and preference. The data were generally consistent with the hypothesis, though some biomechanical advantages were identified for each configuration; specifics and exceptions are discussed, along with reasons for a general recommendation for the use of an external mouse, or mouse and keyboard (without number pad) when using a notebook computer for an extended period of time, as in a desktop replacement scenario.Relevance to industryNotebook computer use is rapidly increasing, in industry and schools. Yet the notebook form factor is inconsistent with a number of current design recommendations. Little research concerning physical ergonomics of notebook computer use has been conducted, so recommendations for use are currently limited and not strongly supported by objective evidence.
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This study evaluated the use of simple inclines as a portable peripheral for improving head and neck postures during notebook computer use on tables in portable environments such as hotel rooms, cafés, and airport lounges. A 3D motion analysis system measured head, neck and right upper extremity postures of 15 participants as they completed a 10 min computer task in six different configurations, all on a fixed height desk: no-incline, 12° incline, 25° incline, no-incline with external mouse, 25° incline with an external mouse, and a commercially available riser with external mouse and keyboard. After completion of the task, subjects rated the configuration for comfort and ease of use and indicated perceived discomfort in several body segments. Compared to the no-incline configuration, use of the 12° incline reduced forward head tilt and neck flexion while increasing wrist extension. The 25° incline further reduced head tilt and neck flexion while further increasing wrist extension. The 25° incline received the lowest comfort and ease of use ratings and the highest perceived discomfort score. For portable, temporary computing environments where internal input devices are used, users may find improved head and neck postures with acceptable wrist extension postures with the utilization of a 12° incline.
Article
Effects of display size and dual display setting on preferred display and keyboard positions were evaluated. User-preferred display position may vary as its size changes or when multiple displays are used. It is also not known whether the use of larger displays or multiple displays would influence positioning of the keyboard. Participants (N=19) who had normal visual acuity (20/30 or better) determined preferred positions of the display and the keyboard during a data entry task in four display setups (19, 24, 27.5, and dual 19 in.). The size of capital characters (3.2 mm high) was kept consistent between setups. Preferred viewing distance ranged from 0.68 m (19-in. display) to 0.76 m (27.5-in. display). No significant differences in viewing distance and display height were found between the single 19-in. display and dual 19-in. displays setups. The preferred position of the keyboard was consistent between display setups. Participants placed larger displays farther and lower while maintaining the display top at or near eye height. Preferred position of the dual displays in landscape setting did not differ from that of a single display. It appears that the preferred display position varies with the vertical dimension of the overall viewable area of the display. The results of this study can be used to determine the dimensions or adjustability of computer workstations for larger displays or multiple displays settings.
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A repeated measures observational study. To investigate change in sagittal alignment of head and neck posture in response to adjustments of an office chair with and without a lumbar roll in situ. Forward head posture has been identified as a risk factor for neck pain, and there is evidence to show that ergonomic correction in sitting may reduce the incidence of pain. The effect placement of a lumbar roll has on cervical spine posture has not been previously investigated experimentally but rather, is assumed to have a positive influence on head and neck posture. Thirty healthy male participants (18-30 years) were photographed while registered in the natural head resting position in each of 4 sitting positions with and without a lumbar roll in situ. Two positions incorporated adjustments to the back rest and 1 to the seat pan of the office chair. The craniovertebral (CV) angle, as a determinant of head and neck posture was measured from the set of digitized photographs obtained for each participant. Comparisons between the CV angle in all postural registrations were made using a mixed model analysis adjusted for multiple comparisons. Of the positions examined, significant differences in the mean CV angles were found with the backrest of the chair at 100 degrees and at 110 degrees (P < 0.001). With the lumbar roll in situ and the backrest position at 110 degrees , there was a significant increase in the mean CV compared with the angle without the lumbar roll in situ (2.32 degrees , 95% confidence interval: 1.31-3.33; P < 0.001). The degree of angulation of the backrest support of an office chair plus the addition of lumbar roll support are the 2 most important factors to be taken into account when considering seating factors likely to favorably change head and neck postural alignment, at least in asymptomatic subjects.