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Work 62 (2019) 27–35
DOI:10.3233/WOR-162839
IOS Press
27
Influence of the wearable posture
correction sensor on head and neck posture:
Sitting and standing workstations
Ravi Charan Ailnenia, Kartheek Reddy Syamalaa, In-Sop Kimband Jaejin Hwanga,∗
aDepartment of Industrial and Systems Engineering, Northern Illinois University, DeKalb, IL, USA
bSchool of Allied Health and Communicative Disorders, Northern Illinois University, DeKalb, IL, USA
Received 8 December 2017
Accepted 21 May 2018
Abstract.
BACKGROUND: Flexed head and neck postures are associated with the development of neck pain in the office environment.
There is little evidence regarding whether a wearable posture sensor would improve the head and neck postures of office
workers.
OBJECTIVE: The aim of this study was to evaluate the effect of the wearable posture sensor on the posture and physical
demands on the head and neck during office work.
METHODS: Nineteen participants performed a typing task with and without the wearable sensor in the sitting and standing
positions. They were allowed to adjust their workstation during the experiment based on a psychophysical method. The
flexion angles of the head and neck, the gravitational moment on the neck, and the positions of the workstation components
were measured.
RESULTS: On average, participants with the wearable sensor had 8% lower neck flexion angles and 14% lower gravitational
moments on the neck than those of participants without the wearable sensor. The effect of the wearable sensor on reducing
postural stress of the neck was more significant when using the standing workstation compared to the sitting workstation.
CONCLUSIONS: The wearable posture sensor could be an effective tool to alleviate the postural stress of the neck in the
office setting.
Keywords: Wearable sensor, posture, workstation, biomechanics, psychophysics
1. Introduction
Office workers typically sit for six hours per day
during work [1]. Prolonged sedentary work has been
associated with adverse health effects, including mus-
culoskeletal disorders [2–4], cardiovascular disorders
[5, 6], and type II diabetes [7]. The lack of motion
in the sitting environment is known to affect low
circulatory demands [8] and muscle activations [9].
∗Address for correspondence: Jaejin Hwang, Department of
Industrial and Systems Engineering, Northern Illinois University,
590 Garden Road, EB230, DeKalb, IL 60115, USA. Tel.: +1 815
753 9980; E-mail: jhwang3@niu.edu.
Flexed head and neck postures have been found
to be risk factors for neck pain in the office environ-
ment [10–14]. For instance, a recent study showed
that tablet computer usage increases the physical
demand of the neck 3 to 5 times compared to the
neutral posture in sitting [10]. In terms of biome-
chanics, an increased neck flexion angle is related to
an increase of the gravitational moment on the neck
[12, 15, 16]. Compared to neutral posture, the higher
demand of the gravitational moment in the flexed pos-
ture requires greater activation of neck muscles [17],
which leads to muscle fatigue and increases risk of
neck pain [18].
ISSN 1051-9815/19/$35.00 © 2019 – IOS Press and the authors. All rights reserved
28 R.C. Ailneni et al. / Influence of a wearable posture correction sensor
To alleviate the adverse effects of substantial head
and neck flexion in the office environment, several
administrative and engineering controls have been
suggested. For instance, previous studies found that
an accessory stand for the tablet or laptop can reduce
flexion angles of the head and neck and decrease mus-
cle activities of the neck [10, 11, 19]. Despite the
positive results of the accessory stand on reducing
postural stress of the neck, the long-term effects of
ergonomic training on musculoskeletal disorders of
office workers are still controversial [20, 21]. Proper
ergonomic training and sustained usage of ergonomic
interventions are still challenging issues in the office
environment [22, 23].
Wearable posture correction sensors might be
a useful tool to help office workers maintain good,
upright postures in the office environment. A previ-
ous study showed that a wearable sensor that tracks
the user’s postures and gives light vibration feedback
in real-time is effective at improving posture over 25
days [24]. Despite this promising result, there is lit-
tle evidence that wearable posture sensors reduce the
flexion angles and physical demands of the head and
neck when using sitting and standing workstations.
The objective of this study was to investigate
whether a wearable posture sensor reduces the postu-
ral stress of the head and neck in sitting and standing
workstations. Our first hypothesis was that the wear-
able sensor feedback would help participants reduce
flexion angles of the head and neck, thereby decreas-
ing the gravitational moment on the neck relative
to that of participants without the wearable sensor.
Our second hypothesis was that the wearable sensor
would assist participants in finding better workstation
configurations that alleviate physical demand, includ-
ing the heights of the chair and desk and tilt angle of
the laptop, compared to participants without the aid
of the wearable sensor.
2. Methods
2.1. Participants
A total of 19 participants (10 females and 9 males)
were recruited for the study. All participants provided
informed consent per Institutional Review Board
requirements prior to participation in the study. The
inclusion criteria were that the participant should
have a typing speed of at least 30 words per minute
(WPM) and should not have had any pain in the
upper extremities or lower back region within the past
7 days. The means (standard deviation) of age, height,
body mass, and head circumference of the partic-
ipants were 24.47 (5.32) years, 167.98 (12.25) cm,
66.79 (9.30) kg, and 54.53 (2.84) cm, respectively.
The detailed anthropometric information is summa-
rized in Table 1.
2.2. Instrumentation
Kinematics data of the head, neck, and positions
of the workstation components (desk, chair, and lap-
top) were continuously collected during the task
using an optical motion capture system with six Flex
13 infrared cameras (Natural Point, Corvallis, OR,
USA) at a sampling rate of 100 Hz. A customized
Matlab program (R2015a, MathWorks, Natick, MA,
USA) was utilized to compute joint angles and joint
moments of the head and neck. The posture correc-
tion wearable sensor (Alex, NAMU Inc., Seoul, South
Korea) was positioned on the posterior side of the
participant’s neck. This device consisted of a 3-axis
accelerometer to measure posture and movement of
the neck in real time, and it sends this information
to the companion smartphone app through Bluetooth
for the posture management. This device measures
the gravitational force on the sensor in a static pos-
ture then computes the neck flexion angle [25]. When
a participant maintained a poor neck posture (a neck
flexion angle greater than 15◦relative to the neu-
tral posture) for more than 30 seconds, the wearable
sensor gently vibrated in real-time to remind the par-
ticipant to correct their posture. We determined the
15◦flexion as a threshold since previous study found
15◦forward bending had 2–3 times greater stress on
the neck compared to the neutral posture [26].
2.3. Testing procedure
Anthropometric measures including the height,
body mass, and head circumference of each partic-
Table 1
Mean and standard deviation of participant anthropometry
Age (years) Height (cm) Body mass (kg) Head circumference (cm)
Males (n= 9) 24.33 ±2.24 174.07 ±6.18 72.23 ±9.43 55.59 ±2.03
Females (n= 10) 24.06 ±7.21 162.49 ±13.99 61.88 ±6.14 53.57 ±3.21
Total (n=19) 24.47 ±5.32 167.98 ±12.25 66.79 ±9.30 54.53 ±2.84
R.C. Ailneni et al. / Influence of a wearable posture correction sensor 29
ipant were collected at the beginning of the study.
Seven reflective markers were placed on the partic-
ipant’s left and right canthus, left and right tragus,
C7 spinous process, sternal notch, and the vertex of
the head to calculate joint angles and gravitational
moment of the head and neck. Eight reflective mark-
ers were placed on the ground, chair, edge of the desk,
and laptop to compute the height of the desk and chair,
as well as the laptop tilt angle.
The participants were asked to type continuously
using typing software (Typing Master 10) with and
without the wearable sensor in the sitting and standing
workstations. A total of four conditions were random-
ized, and each condition consisted of a 30-minute
typing task. The contents of the typing tasks were
varied between conditions of each participant to min-
imize the learning effect. Five-minute breaks were
provided to the participants between conditions to
minimize carryover fatigue. The experimental setup
is shown in (Fig. 1).
At the beginning of each task, the laptop was
located at the left edge of the desk, and the height
of the desk and the chair were set to the lowest level
in the sitting workstation, or the desk was set to the
highest level in the standing workstation. Each partic-
ipant initially adjusted their workstation components.
Based on the psychophysical method [27], partici-
pants were instructed to adjust the tilt angle of the
laptop screen and the height of the desk and chair
to their preference. They could also adjust them in
the middle of the task if they wanted. They were
instructed to keep adjusting their workstation as if
they were comfortably working a full 8-hour day.
This method was found to be a robust and effective
method to determine a participant’s preferred setup
of the sitting and standing workstations [28].
2.4. Data analysis
Independent variables included the presence of
the wearable sensor (with or without). Dependent
variables included the neck flexion angle, head
flexion angle, cranio-cervical angle, gaze angle,
gaze distance, C7-T1 gravitational moment, C7-T1
moment-arm, laptop tilt angle, chair height, desk
height, typing speed, and typing accuracy. Figure 2
illustrates the dependent variables. The neck flexion
angle was defined as the angle between the vertical
line at the C7 spinous process and the vector point-
ing from the C7 spinous process to the mid-tragus
(midpoint between left and right tragus). The head
flexion angle was defined as the angle between the
vertical line at the mid-tragus and the vector point-
ing from the mid-tragus to the mid-canthus (midpoint
between left and right canthus). The cranio-cervical
angle was defined as the angle between the vector
pointing from the mid-tragus to the C7 spinous pro-
cess and the vector pointing from the mid-tragus to
the mid-canthus. The gaze angle was defined as the
angle between a horizontal line at the mid-canthus
and the vector pointing from the mid-canthus to the
center of the laptop screen. Gaze distance was com-
puted from the mid-canthus to the center of the laptop
screen.
Fig. 1. Experimental setup. (a): with wearable sensor while sitting, (b): with wearable sensor while standing, and (c): the wearable sensor
positioned on the neck.
30 R.C. Ailneni et al. / Influence of a wearable posture correction sensor
Fig. 2. Illustration of dependent variables. ①: neck flexion angle, ②: head flexion angle, ③: cranio-cervical angle, ④: gaze angle, ⑤: gaze
distance, ⑥: laptop tilt angle, ⑦: gravitational moment on the neck, and ⑧: gravitational moment-arm of the neck. Solid circle: reflective
markers, and dotted circle: virtual marker.
The gravitational moment was calculated from the
product of the head mass and the perpendicular dis-
tance between the vertical axis at the center of gravity
(COG) of the head and C7-T1. The COG was esti-
mated as 17% of the distance from the mid-tragus to
the vertex of the head [29]. The head mass was esti-
mated using a regression equation based on the head
circumference and the body mass [30]. The C7-T1
position was estimated from the midpoint between
the sternal notch marker and the C7 spinous process
marker [31].
The average values of the joint angle, gravita-
tional moment of the head and neck, and workstation
positions were calculated during the last 6 minutes
(minute 24 to 30) of each condition to represent the
participant’s final preferred workstation configura-
tion and associated posture [28]. A previous study
showed that the participant gradually settled into
a preferred workstation configuration within 11.25
minutes while sitting or standing [28]. Thus, we
assumed that the 30-minute task period would be
a reasonable duration to find convergence of the
workstation and associated posture.
2.5. Statistical analysis
For normally distributed data, a paired t-test was
conducted using SPSS 24 software at a significance
level of 0.05. If the data were not normally dis-
tributed, a Wilcoxon signed-rank test was conducted.
The mean and standard error of each dependent vari-
able was summarized.
3. Results
3.1. Head and neck postures
The number of vibrations that occurred from the
wearable sensor decreased over time in the sitting and
standing workstations (Fig. 3). The average number
of vibrations was less than one during the last interval
R.C. Ailneni et al. / Influence of a wearable posture correction sensor 31
Fig. 3. Mean and standard error of (a) the number of vibrations occurred from the wearable sensor, and (b) height of the desk and chair over
time while sitting and standing. Each data point represented the average values of the preceding 6-minute interval.
Table 2
Mean and standard error of final preferred workstation configuration and associated
head and neck postures in the sitting workstation
Variables p-values Wearable sensor
With Without
Neck flexion angle (◦) 0.002∗57.52 (1.25) 63.16 (1.83)
Head flexion angle (◦) 0.156 80.22 (1.85) 81.96 (2.08)
Cranio-Cervical angle (◦) 0.001∗157.14 (1.89) 160.90 (2.00)
Gaze angle (◦) 0.106 –30.51 (1.40) –32.02 (1.36)
Gaze distance (cm) 0.068 56.17 (1.50) 53.43 (1.90)
Laptop tilt angle (◦) 0.732 113.96 (2.19) 113.54 (1.68)
Neck moment (Nm) 0.028∗2.60 (0.16) 3.00 (0.20)
Neck moment-arm (cm) 0.028∗5.92 (0.35) 6.82 (0.42)
Chair height (cm) 0.863 44.27 (0.90) 44.42 (0.90)
Desk height (cm) 0.338 73.17 (1.27) 72.03 (1.12)
Typing accuracy (%) 0.473 92.53 (0.98) 93.21 (0.87)
Typing speed (WPM) 0.297 38.63 (2.95) 39.05 (2.53)
Note: Mean and standard error of each variable was summarized. ∗p-values < 0.05.
The Wilcoxon signed ranks test was conducted for typing accuracy and speed.
(24 to 30 minutes). In addition, the average differ-
ences between the desk and chair heights between the
fourth interval (18 to 24 minutes) and the last inter-
val (24 minute to 30 minute) were less than 0.3 cm
(Fig. 3). This was indicative of the convergence of the
workstation configuration at the end of each condition
for the participants. Thus, only the final preferred con-
figuration and associated posture in the last interval
were considered in the following analysis.
Table 2 shows the mean and standard error of each
dependent variable, with p-values, while sitting. With
the aid of the wearable sensor, participants showed
significantly lower neck flexion angles (p= 0.002)
and cranio-cervical angles (p= 0.001) compared to
those of participants without the wearable sensor.
The neck flexion and cranio-cervical angles were
decreased by 6 and 4 degrees when participants wore
the sensor.
32 R.C. Ailneni et al. / Influence of a wearable posture correction sensor
Table 3
Mean and standard error of final preferred workstation configuration and associated
head and neck postures in the standing workstation
Variables p-values Wearable sensor
With Without
Neck flexion angle (◦) <0.0001∗58.49 (1.11) 63.21 (1.38)
Head flexion angle (◦) 0.038∗81.32 (2.01) 84.35 (1.69)
Cranio-Cervical angle (◦) 0.298 157.09 (2.06) 158.22 (1.87)
Gaze angle (◦) 0.126 –34.04 (1.69) –35.67 (1.59)
Gaze distance (cm) 0.018∗55.76 (1.91) 53.55 (2.13)
Laptop tilt angle (◦) 0.372 116.96 (1.93) 115.24 (2.38)
Neck moment (Nm) <0.0001∗2.69 (0.11) 3.18 (0.12)
Neck moment-arm (cm) <0.0001∗6.16 (0.27) 7.24 (0.26)
Desk height (cm) 0.320 111.62 (1.83) 110.14 (1.48)
Typing accuracy (%) 0.415 93.37 (0.85) 93.68 (0.71)
Typing speed (WPM) 0.209 38.84 (2.92) 39.63 (3.10)
Note: Mean and standard error of each variable was summarized. ∗p-values < 0.05.
The Wilcoxon signed ranks test was conducted for typing accuracy and speed.
Table 3 shows the mean and standard error of each
dependent variable, with p-values, while standing.
With the wearable sensor, participants showed sig-
nificantly lower neck flexion angles (p< 0.0001) and
head flexion angles (p= 0.038) compared to those of
participants without the wearable sensor. The neck
flexion and head flexion angles were reduced by 5 and
3 degrees while wearing the sensor. With the wear-
able sensor, participants had significantly longer gaze
distance (p= 0.018) than did participants without the
wearable sensor. The gaze distance was increased by
2 cm when wearing the sensor.
3.2. Gravitational moment on the neck
There was a significant effect of the wearable sen-
sor on the gravitational moment and moment-arms at
C7-T1 while sitting and standing (Tables 2 and 3).
With the wearable sensor, participants showed lower
gravitational moments and moment-arms compared
to without the wearable sensor. The statistical sig-
nificance was greater in the standing workstation
(p< 0.0001) than the sitting workstation (p= 0.028).
When participant wore the sensor, the gravita-
tional moment and moment-arm were decreased
by 0.4 Nm and 1 cm in the sitting workstation,
and reduced by 0.5 Nm and 1 cm in the standing
workstation.
3.3. Typing accuracy and speed
Typing accuracy and speed were not significantly
different with and without the wearable sensor for
either the sitting or standing workstations (Tables 2
and 3). Average typing accuracy ranged from 92.53%
to 93.68%, and average typing speed ranged from
38.63 to 39.63 WPM.
4. Discussion
The objective of this study was to investigate the
effect of the wearable posture correction sensor on
the preferred workstation setup and associated pos-
tures of the head and neck while sitting and standing.
The results showed that the wearable sensor assisted
participants in achieving more upright postures of
the head and neck (reduced flexion angles and grav-
itational moments) compared to without wearable
sensor. This result supported the first hypothesis that
the wearable posture sensor would reduce the flexed
head and neck postures of participants and alleviate
the gravitational moment on the neck.
Regardless of the wearable sensor, participants had
similar preferred workstation setups, including the
desk height, chair height, and laptop tilt angle for
sitting and standing at the last interval (24 to 30 min-
utes) of the study. This result did not support our
second hypothesis that the wearable sensor would
assist participants in having a more upright posture
than without the wearable sensor. In addition, there
was no significant difference in typing performance
with and without the wearable sensor.
The neck flexion angle was significantly different
with and without the wearable sensor for the sitting
(p= 0.002) and standing (p< 0.0001) workstations.
The effect of the wearable sensor on the neck flexion
angle was more significant in the standing work-
station in comparison with the sitting workstation.
R.C. Ailneni et al. / Influence of a wearable posture correction sensor 33
Participants with the wearable sensor in the sit-
ting position showed the lowest neck flexion angle
(57.52◦), while participants without the wearable sen-
sor in the standing position showed the highest neck
flexion angle (63.21◦). The range of values in the
present study was comparable to a previous study
(55.0◦to 60.2◦) in which participants typed with
a tablet computer in different positions [10]. For
example, the neck flexion angle with the wearable
sensor in the sitting condition (57.52◦) was compara-
ble to the more upright posture condition (desk high
while reading, 56.8◦), with the exception of neutral
posture, reported in the previous study [10].
The head flexion angle was significantly differ-
ent (p= 0.038) with and without the wearable sensor
in the standing workstation. Standing participants
with the wearable sensor showed a less flexed pos-
ture (81.32◦) than those without the wearable sensor
(84.35◦). This finding was comparable to the range
of values (85◦to 107.3◦) from previous studies that
investigated the interaction of individuals with tablet
devices and their positions [10, 11]. For example, the
head flexion angle with the wearable sensor while sit-
ting (80.22◦) was comparable to the lowest demand
condition (movie watching with the tablet, 85◦)
reported in the previous study [11].
The cranio-cervical angle was significantly dif-
ferent (p= 0.001) with and without the wearable
sensor while sitting. While sitting, the wearable sen-
sor resulted in a smaller angle (157.15◦) than that
without the wearable sensor (160.90◦). The cranio-
cervical angle is the combination of the neck and head
flexion angles. The head flexion angle did not signif-
icantly vary (p= 0.156) with and without wearable
sensor while sitting. Therefore, the cranio-cervical
angle was mainly influenced by the neck flexion angle
with (57.52◦) and without (63.16◦) the wearable
sensor.
The average gravitational moment on the neck,
which ranged from 2.60 Nm (with the wearable sen-
sor in sitting) to 3.18 Nm (without the wearable
sensor in standing), was significantly different with
and without the wearable sensor for sitting (p= 0.028)
and standing (p< 0.0001). The effect of the wear-
able sensor on the gravitational moment was more
significant in the standing workstation. Our find-
ing was comparable to the range (3 to 3.8 Nm) of
the previous study that included typing with the
tablet device [10]. Participants without the wear-
able sensor in the standing workstation showed a 1.2
times greater gravitational moment than participants
with the wearable sensor in the sitting workstation.
Previous studies showed that a 1.47 to 1.5 times
greater gravitational demand occurs at the desk flat
position compared to the desk high position [10, 12].
The gravitational moment with the wearable sen-
sor in sitting (2.60 Nm) was comparable to the desk
high reading position (approximately 3 Nm), the low-
est demand condition with the tablet in the previous
study [10].
Participants with the wearable sensor had a signif-
icantly (p= 0.018) longer gaze distance (55.76 cm)
than without the wearable sensor (53.55 cm) while
standing, and the range of gaze distances was similar
to the range of the previous study [11]. A greater gaze
distance was associated with a reduced neck flexion
angle with the wearable sensor (58.49◦) compared
to without the wearable sensor (63.21◦). The pre-
vious study reported that a gaze angle below –45◦
is associated with significantly higher strain on the
neck extensors [12]. In the present study, the gaze
angle ranged from –35.67◦(without the wearable sen-
sor, standing) to –30.51◦(with the wearable sensor,
sitting), above the threshold (–45◦) reported in the
previous study [12].
There were no significant differences of the work-
station configuration setups, including the chair
height, desk height, and laptop tilt angle, with and
without the wearable sensor. Based on the psy-
chophysical methods implemented in this study, we
found that participants settled on a similar preferred
setup, regardless of the wearable sensor. This indi-
cates that the significant differences of the neck
and head flexion angles and gravitational moment
with and without the wearable sensor were mainly
influenced by posture. In other words, given simi-
lar configurations of the workstations while sitting
and standing, participants tended to approach upright
postures more with the aid of the wearable sensor
compared to without the wearable sensor.
For the sitting workstation, the participants pre-
ferred chair and desk heights were approximately
44 and 73 cm, respectively. A previous study found
that the user’s preferred desk height in sitting is
74 cm, close to our finding [28]. For the standing
workstation, the preferred desk height of participants
was approximately 111 cm, higher than the preferred
desk height (98 cm) reported in the previous study
[28]. The difference might be due to the different
tasks conducted by the participants and the different
devices used in the two studies. The present study
involved typing with a laptop, while the previous
study involved one third keyboard work and two
thirds mouse work with the desktop setting [28].
34 R.C. Ailneni et al. / Influence of a wearable posture correction sensor
There were several limitations in this study. Only
healthy young participants were recruited. Elderly
participants, who have different cognitive and motor
functions, might behave differently given the same
psychophysical experiment setup. This was a labo-
ratory study to investigate the effect of the wearable
sensor on head and neck postures in simulated office
work. Even though we found some potential ben-
efits of the wearable posture sensor on reducing
physical demands on the neck, the long-term effect
of the wearable sensor on the physical stress of
the neck in daily life is still unknown. Neck mus-
cle fatigue was not addressed in this study. Each
condition consisted of a 30-minute task, and the mus-
cle activity was not monitored in this study. Future
studies might address the effect of the wearable sen-
sor on neck muscle fatigue in the longer duration
task. The commercial wearable sensor used in this
study was not directly validated or calibrated in our
laboratory. This sensor might result in lower sensi-
tivity to estimate neck angles in walking due to the
external accelerations of the movement [25]. Since
participants had static postures (Fig. 3: number of
vibration was less than 1 in last period), we expect
that the measurement error of the sensor would be
minimal.
5. Conclusions
The potential benefit of the wearable posture
correction sensor was investigated to find whether
participants could improve their head and neck pos-
tures in office work. With the assistance of the
wearable sensor, participants had 8% lower neck flex-
ion postures and 14% lower gravitational moments on
the neck, compared to without the wearable sensor for
the sitting and standing workstations. The effect of
the wearable sensor on the physical demands on the
neck was more significant in the standing worksta-
tion compared to the sitting workstation. The present
study showed that the wearable sensor could be an
effective tool to alleviate postural stress of the head
and neck in sedentary work. Our findings will be help-
ful to improve the design of the wearable sensor and to
develop ergonomic guidelines for using the wearable
sensor during office work.
Conflict of interest
None to report.
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