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International Journal of Occupational Safety and
Ergonomics
ISSN: 1080-3548 (Print) 2376-9130 (Online) Journal homepage: http://www.tandfonline.com/loi/tose20
Impact of rest-break interventions on the neck
and shoulder posture of symptomatic VDU
operators during prolonged computer work
Montakarn Chaikumarn, Nuttika Nakphet & Prawit Janwantanakul
To cite this article: Montakarn Chaikumarn, Nuttika Nakphet & Prawit Janwantanakul (2017):
Impact of rest-break interventions on the neck and shoulder posture of symptomatic VDU
operators during prolonged computer work, International Journal of Occupational Safety and
Ergonomics, DOI: 10.1080/10803548.2016.1267469
To link to this article: http://dx.doi.org/10.1080/10803548.2016.1267469
Accepted author version posted online: 01
Dec 2016.
Published online: 06 Jan 2017.
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International Journal of Occupational Safety and Ergonomics (JOSE), 2017
http://dx.doi.org/10.1080/10803548.2016.1267469
Impact of rest-break interventions on the neck and shoulder posture of symptomatic VDU
operators during prolonged computer work
Montakarn Chaikumarna∗, Nuttika Nakphetband Prawit Janwantanakula
aFaculty of Allied Health Sciences, Chulalongkorn University, Thailand; bFaculty of Physical Therapy, Rangsit University, Thailand
There is limited research on the effects of different types of rest-break interventions for visual display unit (VDU) operators
on neck and shoulder postures. This study examined the effect of rest-break interventions on the neck and shoulder postures
of symptomatic VDU operators during prolonged computer work. Thirty subjects were randomly and equally assigned to
breaks with stretching, breaks with dynamic movement and passive breaks. Subjects performed the typing task for 60 min
and received 3-min breaks after 20 min of work. The craniovertebral and forward shoulder angles were obtained from a
3D motion analysis system. Results showed that there were no significant differences in the craniovertebral and forward
shoulder angles among any types of rest breaks. It can be concluded that the three types of rest-break interventions had
positive effects on neck and shoulder posture during prolonged computer terminal work.
Keywords: symptomatic VDU operators; rest break; neck and shoulder postures
1. Introduction
Visual display units (VDUs) have become widely and
routinely used in modern workplaces [1]. Epidemiology
studies reported that neck and shoulder symptoms in VDU
operators are associated with long periods of computer use
[2,3]. The prevalence of musculoskeletal disorders (MSDs)
has been found to be associated with VDU work [2,4–7].
A cross-sectional survey of female office workers found
that 53% of them had experienced neck pain of mild
intensity [3]. In addition, female computer users are at
higher risk of having MSDs in the neck–shoulder region
[8–11]. Moreover, operators with previous history of neck–
shoulder injuries are at higher risk of neck and upper
extremity MSDs [8,12].
The VDU operators’ forward-bending posture has
shown to be one of increased forward flexion of the head
and the upper back, with the shoulders tended to be more
flexed and less abducted when working on a VDU work
task compared with an ordinary paper task [13]. An appro-
priate posture is considered to be one of musculoskeletal
balance with less stress and strain on the body. Regarding
the VDU operators’ posture, the defining characteristic is
that of remaining in a sitting posture for a prolonged period
while working on VDU tasks. This static sitting posture can
further increase forward neck flexion [14,15]. In addition,
maintenance of a static posture for a prolonged period of
time is considered to be a risk factor for the development
of MSDs [16].
*Corresponding author. Email: cmontaka@chula.ac.th
There are many physical problems caused by forward
head postures such as an increase in upper cervical cur-
vature (C1–C4), a decrease in lower cervical curvature
and protraction, and elevation and downward rotation of
the scapulae [17]. In addition, increased forward head
posture during VDU work results in an increase in mus-
cular activity in the neck–shoulder musculature in order to
hold the head and neck in this position [15], which may
result in muscle fatigue and muscle imbalance. Sustain-
ing an awkward posture also leads to an increase in the
load on non-contractile tissues, which has been considered
an intrinsic factor in the development of MSD symptoms
[18–20].
The working posture of VDU operators has been com-
monly studied in two-dimensional (2D) static posture. Pho-
tographs of the sagittal plane have been used to measure the
2D posture of the head, neck, shoulder and trunk [21,22].
Some studies used video to record the postural profile
to provide information about the extent of the movement
[14,15]. Recently, three-dimensional (3D) motion analysis
systems have been used in ergonomic research to analyse
the movement of the body segments. The advantage of the
3D system is that it can track the movement of multiple
body parts simultaneously. In recent years, some studies
have examined the subject’s posture in response to changes
in the workstation [22], and in response to sitting pos-
ture [23]. However, these studies have been conducted on
healthy pain-free individuals.
© 2017 Central Institute for Labour Protection – National Research Institute (CIOP-PIB)
2M. Chaikumarn et al.
Regarding occupational musculoskeletal load primar-
ily in the neck and shoulder regions, Westgaard and
Winkel [24] suggested guidelines for successful interven-
tions corresponding to musculoskeletal health. The guide-
lines considered a reduction in the dimensions of mechani-
cal exposure as the level of workload and time dimensions
of workload. However, if the exposure level is high and
the work situation does not allow a reduction in exposure
level below a safe limit, guidelines are given concerning
the requirement of rest pauses.
Concerning the dimension of the reduction of expo-
sure level, most studies focusing on workstation design
address desk and display design [25,26]. The workstation
design can influence short-term variation in posture and
muscular variability [25]. However, the workstation design
cannot be changed in every office. Rest breaks have there-
fore been proposed as a means of reducing the static loads
on the musculoskeletal system as well as repetitive strain
injuries associated with prolonged computer work [27–32].
Furthermore, taking frequent rest breaks during work is
considered a practical recommendation because it is not
costly for the workplace [33].
Rest-break interventions during computer work tasks
are classified into active and passive pauses. The passive
pauses in these appraisals mean that the operator leaves
the computer tasks and sits relaxing during this period,
while during the active pause the operator is required to
perform a specific movement such as shoulder elevation
[34,35]. Large variations in the types of activities during
the rest break, such as dynamic movement [28], eccentric
contraction [34], sub-maximal contraction [35] and stretch-
ing [36,37], have been implemented. However, there is still
limited clinical trial research that addresses the effects of
different types of activity during rest-break interventions
for VDU operators in terms of the change in neck and
shoulder postures.
The aim of this study was to examine the effect of
rest-break interventions on the neck and shoulder postures
of symptomatic VDU operators whilst performing a 1-h
computer typing task. In this research, our focus was to
determine which type of activity during rest-break inter-
ventions will be most effective in terms of the positive
impact on the neck and shoulder posture of symptomatic
VDU operators when working in the same workstation
setting.
2. Methods
2.1. Study design
The present research employed a randomized control trial
study design where subjects were randomly allocated into
three groups based on the types of the rest-break inter-
ventions as follows: (a) a reference group with no activity
during breaks; (b) a rest-break intervention with stretching;
and (c) a rest-break intervention with dynamic contrac-
tion. The subjects were reasonably matched in terms of
age, body build, symptoms in the neck–shoulder and work
background. Table 1presents the general characteristics of
the three groups.
2.2. Subjects
Thirty female VDU workers aged 18–40 years were
recruited from universities and offices in Bangkok
(Table 1). The subjects were currently experiencing dis-
comforts in the neck and shoulder areas and had done so
for more than 3 months. The subjects had to perform at
least 4 h of computer work per day. All subjects were right-
hand dominant and had been in their current position for at
least 2 years. The subjects reported an experience of dis-
comfort related to work. Subjects were excluded if they
had the following: body mass index (BMI) over 25 [38], a
history of the onset of symptoms in the area of the neck–
shoulders and arms due to traumatic injury or accident,
surgery on the spine or the shoulder, signs of neurologi-
cal deficits, pregnant or on maternity leave and defects in
eyesight with no correction of eyesight. A physical thera-
pist with 15 years of experience performed all assessments
for inclusion and exclusion criteria. Written consent was
obtained from all subjects. The study was approved by the
Ethics Review Committee for Research Involving Human
Research Subjects, Health Science Group, Chulalongkorn
University.1
2.3. Workstation and task setting
Each subject was provided with an appropriate adjustable
workstation as per the guidelines for setting up a com-
puter workstation by the Occupational Safety and Health
Administration (OSHA) [39]. A standard office chair with
armrests was adjusted to the subject’s popliteal height. The
top of a 40-cm liquid crystal display (LCD) was adjusted
to eye level and the distance between the display and the
user was approximately that of the subject’s reach. A doc-
ument holder was placed on the right side. The subjects
were instructed to sit in a comfortable posture for computer
work. The study was conducted in a motion analysis labo-
ratory room in which the climate, lighting and environment
were controlled.
A paper-based typing task was conducted in this study.
The task required reading from paper sheet documents
placed on the document holder and completing the typ-
ing task in Thai using a keyboard and mouse. The subjects
were asked to type at their normal pace over 60 min. The
subjects could correct any error at all times.
2.4. Rest-break conditions
The subjects were assigned to one of the three groups with
differing conditions of passive break (control), rest break
International Journal of Occupational Safety and Ergonomics (JOSE) 3
with stretching and rest break with dynamic contraction.
In all conditions, the subjects received a 3-min break after
every 20 min of work. The subjects randomly assigned
into the control condition group were provided with 3-min
breaks with no need to perform any activity. They moved
their hands away from the computer and relaxed sitting
back on a chair during breaks.
For those in the rest-break condition with stretching
group, the subjects performed stretching at the bilateral
upper trapezius, lower trapezius, anterior deltoid and cer-
vical erector spinae muscles for 15 s each within a 3-min
break. The subjects received the stretching guidance from
a physical therapist before the actual experiment and they
did the stretching following the video instruction presented
on the LCD display screen during the breaks.
The protocol for stretching was as follows: (a) remov-
ing themselves from the computer work and standing
beside the VDU workstation; (b) stretching and holding for
15 s at sufficient intensity to elicit a feeling of stretch with-
out pain in each muscle, namely right upper trapezius, left
upper trapezius, right lower trapezius, left lower trapez-
ius, both anterior deltoids and cervical erector spinae; and
(c) repeating all of the stretching again. The positions and
movements of stretching are shown in Figure 1.
In the rest-break condition with dynamic contraction,
the subjects performed a full range of motion for eleva-
tion of both shoulders, flexion of both shoulders and neck
extension during 3-min breaks. The dynamic contraction
gradually increases and decreases the length and tension of
the muscles and is called the isotonic contraction. The sub-
jects stood near to the workstation and performed dynamic
contractions following the video instructions for eleva-
tion of both shoulders, flexion of both shoulders and neck
extension. Each movement was done five times. The rate
of movement was set by a metronome at 30 bpm. The
movements are shown in Figure 2.
2.5. Neck–shoulder posture measurement
The data for neck–shoulder postures were collected using
a seven-camera infra-red motion analysis system (Motion
Analysis, USA) at 50 Hz. Three reflective markers (12.5
mm) were placed on the right side of each subject at the
following skeletal landmarks: targus, spinous process of
C7 and lateral tip of acromion process. The markers were
attached to all subjects by the same physical therapist.
To calculate the craniovertebral (CV) and forward
shoulder (FS) angles, commercial software (Kin Tools RT;
Motion Analysis, USA) was used. The CV and FS angles
were derived from data at the 0th, 20th, 23rd, 43rd, 46th
and 66th min of the typing task over the 60-s duration and
following it.
The CV angle was the angle between the line from the
tragus to the C7 line and the xaxis at C7. The FS angle
was the angle between the line from the tragus to the C7
line and the xaxis at C7 [40]. Figure 3shows the CV angle
and FS angle.
Before performing video capture, the motion analysis
system was calibrated to determine the exact positions and
orientation of the cameras. The calibration frame and wand
were used to determine the reconstruction volume.
2.6. Experimental procedure
The experiment was conducted in the morning. The refer-
ence sitting posture was recorded for 2 min as a baseline
measurement in order to ascertain the subjects’ normal sit-
ting posture before performing the VDU work. The neck
and shoulder postures were recorded by a 3D motion analy-
sis system during 1 h of VDU work. Each subject received
a 3-min rest break after 20 min of work until the 60 min
were completed.
2.7. Statistical analysis
SPSS version 17.0 was used to perform the statistical anal-
yses and significance was set at p<0.05. The subjects
were matched in terms of the characteristics of work pro-
file, anthropometry and age. Repeated-measures analysis
of variance (ANOVA) was used to test for the main effect
of the rest-break interventions for the dependent variables
as the CV angle and the FS angle. The normal distribution
of data was tested using the Kolmogorov–Smirnov test. To
examine the effects of the rest-break intervention on the
CV and FS angles, time was introduced as a factor in a
repeated-measure ANOVA with six levels (0th, 20th, 23rd,
43rd, 46th and 66th min). The sphericity test was used for
any repeated-measures factors. If the assumption indicated
a lack of sphericity, a Greenhouse–Geisser correction was
used. If there were significant effects, post-hoc tests were
applied to locate differences.
3. Results
3.1. Subjects
Group characteristics of subjects are summarized in
Table 1. There were no significant differences between
groups in terms of age, BMI, work profile (work in the
current position, computer use per day) and muscular
discomfort level in the neck and shoulders.
3.2. Craniovertebral angle and forward shoulder angle
A summary of the mean (SD) of the CV angle and the FS
angle of each intervention group is presented in Table 2.
A summary of the repeated-measure ANOVA on CV
and FS angles with the factors time at six levels (0th min
[T0]), at the end of each 20-min working session (20th min
[T1], T3 and T5) and immediately after each break (23rd
4M. Chaikumarn et al.
(a)
(c)
(b)
(d)
Figure 1. Stretching intervention: (a) upper trapezius; (b) lower trapezius; (c) anterior deltoid; (d) cervical erector spinae.
[T2] and T4]) and rest-break intervention group (reference,
stretching, dynamic) is presented in Table 3.
There was no significant group effect on the CV angle.
There was no significant time effect on the CV angle. How-
ever, there was a significant group ×time interaction effect
on the CV angle (F(10,135) =3.31, p=0.001).
There were significant time effects on the FS angle
(F(3.13, 84.53) =5.07, p=0.002). Post-hoc contrasts
were conducted to explore any significant patterns in the
effect on time. Thus, there was a significant effect of time
on the FS angle between T1 and T3, T2 and T3, and T2 and
T4 (Figure 4).
In addition, there was a significant group ×time inter-
action on the FS angle (F(6.26, 84.53) =3.06, p=0.008)
(Figure 4).
4. Discussion
4.1. Subjects
The subjects in each group were only female VDU oper-
ators with neck and shoulder discomfort. There were
no differences in age, BMI, computer use per day, and
muscular discomfort among groups. However, subjects in
International Journal of Occupational Safety and Ergonomics (JOSE) 5
(a) (c)(b)
Figure 2. Dynamic contraction intervention: (a) shoulder elevation; (b) shoulder flexion; (c) neck extension.
Figure 3. Craniovertebral (CV) angle and forward shoulder
(FS) angle.
the dynamic group had higher muscular discomfort than
the others. A strength of this experiment could thus be that
the subjects all shared the same characteristic.
4.2. Craniovertebral angle
The risk of developing MSDs related to posture resulted
from an increased gravity-resisting moment with decreased
CV angle [41]. Smaller CV angles indicate greater
Table 1. Characteristics of the study subjects.
Subject’s
characteristic
Reference
(n=10)
Stretching
(n=10)
Dynamic
contraction
(n=10)
Age (years) 27.6 (3.0) 31.4 (5.9) 29.6 (5.9)
BMI 20.4 (1.5) 20.6 (2.2) 20.0 (1.8)
Height (cm) 156.6 (5.4) 158.0 (4.8) 159.7 (4.8)
Body weight (kg) 50.2 (5.3) 51.5 (6.0) 51.0 (4.4)
Work in current
position (years)
3.3 (1.3) 4.6 (4.1) 5.2 (4.3)
Computer use per
day (h)
7.2 (1.3) 6.5 (0.5) 6.6 (1.5)
Neck discomfort 3.3 (1.8) 3.4 (1.1) 5.3 (2.7)
Right shoulder
discomfort
3.4 (1.6) 2.7 (1.5) 4.7 (3.1)
Note: Data presented as M(SD). BMI =body mass index.
protraction of the head which means a forward head pos-
ture [42]. Increased flexion at the atlanto-occipital joint and
also increased horizontal distance of the centre of mass
of the head from its axis of rotation is a consequence
of an increased extensor moment [43]. Straker et al. [41]
also suggested that the increased neck flexion angle during
working increased the moment around both the lower and
upper cervical spine and led to increased stress on tissue
and greater risk of developing MSDs.
In the present study, there were no significant dif-
ferences of group effect on the CV angle. However, the
stretching and dynamic contraction groups revealed an
increase in the CV angle after the typing task for 60 min
compared with that of the reference group. In contrast,
Szeto et al. [15] reported that symptomatic office workers
demonstrated an approximate 10% increase in forward
head posture when working with a computer. This result
6M. Chaikumarn et al.
Table 2. Mean (SD) of craniovertebral (CV) angle and forward shoulder (FS) angle.
Time
Rest-breakinterventionT0T1T2T3T4T5
CV
Reference 53.25 ±7.07 52.95 ±7.92 53.10 ±8.86 51.12 ±7.58 52.52 ±7.93 50.04 ±8.05
Stretching 53.44 ±6.09 52.72 ±4.97 53.89 ±4.96 53.64 ±5.58 54.41 ±5.14 55.03 ±4.04
Dynamic contraction 54.12 ±6.03 52.34 ±5.60 53.01 ±5.00 54.63 ±5.22 52.71 ±5.38 52.72 ±6.36
FS
Reference 70.13 ±5.28 70.17 ±5.41 68.88 ±5.25 65.73 ±5.20 66.43 ±6.14 68.24 ±6.63
Stretching 70.97 ±4.83 70.84 ±5.72 71.25 ±5.38 70.72 ±5.68 70.73 ±6.13 68.87 ±6.50
Dynamic contraction 68.54 ±5.38 68.34 ±5.20 69.16 ±5.08 67.44 ±5.22 68.45 ±5.40 68.63 ±5.10
Note: T0 =0th min; T1, T3, T5 =at the end of each 20-min working session; T2, T4 =immediately after each break.
Table 3. Summary of repeated-measure analysis of variance on craniovertebral and forward shoulder angle with the factors time at
six levels (before commencing the typing task, at the end of each 20-min working session, and immediately after each break) and
rest-break intervention group (reference, stretching, dynamic contraction).
Factor
Characteristic Group Time Group ×time
Craniovertebral angle F(2, 27) =1.99, p=0.82 F(5, 135) =1.12, p=0.35 F(10, 135) =3.31, p=0.001*
Forward shoulder angle F(2, 27) =0.60, p=0.56 F(3.13, 84.53) =5.07, p=0.002* F(6.26, 84.53) =3.06, p=0.008*
Note: *Significance level at 0.05
showed that stretching and dynamic contraction activities
during rest-break interventions are assumed to have a pos-
itive influence on the CV angle among the symptomatic
VDU operators during prolonged computer typing tasks.
It was suggested that this was because the larger the CV
angle, the better the posture of head/neck alignment in the
sagittal plane of young females [42].
4.3. Forward shoulder angle
The FS angle provides a measurement of the forward
shoulder position. A smaller angle indicates that the
shoulder is further forward in relation to C7; in other
words, more rounded shoulders [21].
Although there was no significant group effect on the
FS angle, there were significant time effects on the FS
Figure 4. Forward shoulder (FS) angle of the subjects across time.
Note: T0 =0th min; T1, T3, T5 =at the end of each 20-min working session; T2, T4 =immediately after each break.
International Journal of Occupational Safety and Ergonomics (JOSE) 7
angle. We found that the FS angle was reduced after typing
for 20 min (from 23rd to 43rd min) in the reference group.
This means that even though the subjects had a rest break
before each typing session, it was not enough to prevent
forward shoulder posture among them. In contrast, the FS
angle of the stretching and dynamic groups increased after
having rest-break interventions. Szeto et al. [15] studied the
shoulder posture of symptomatic and asymptomatic office
workers, and found the former tended to have more pro-
tracted acromions (smaller FS angle) when compared with
the latter. Thus, our results indicate that rest-break inter-
ventions in the form of stretching and dynamic contraction
could positively affect shoulder posture in symptomatic
VDU operators.
Because of less variability and low levels of upper
trapezius activity during VDU work for prolonged periods,
neck and shoulder MSDs can develop. Furthermore, such
a phenomenon can result in an increase in static posture
[13,44]. Such a posture interrupts circulation and limits
movement. If this is maintained for prolonged periods,
muscle imbalances will develop due to some muscles being
overused and others underused [6]. In addition, dynamic
contraction by performing simple exercises for the neck
and shoulders during breaks could enhance muscle oxy-
genation and blood volume during the performance of
VDU work [35]. Moreover, active stretching during rest-
break intervention involves increasing flexibility around
the neck and shoulder (upper trapezius, lower trapez-
ius, anterior deltoid and cervical erector spinae) which
could help with correcting posture when returning to the
computer work.
4.4. Rest-break intervention
The first hypothesis of this study was that the two active
breaks compare with passive break would cause larger
increases in CV and FS angles. The present study did
not found significant differences in the CV and FS angles
among three types of rest break. However, stretching and
dynamic contraction showed a greater trend of a positive
effect on the CV and FS angles for the symptomatic VDU
operators. This is in line with a previous study reporting
that active breaks with stretching and joint mobilization
significantly improve muscular discomfort compared with
passive breaks [45]. This could positively affect the joint
position of the neck–shoulders in the CV and FS angles
of the subjects.Furthermore, Blangsted et al. [46] reported
that passive breaks are insufficient to attain complete relax-
ation of the trapezius muscle. As regards the neck–shoulder
posture, the trapezius muscle is the main stabilizer. If
the trapezius is fatigued during prolonged computer work,
the CV and FS angles could be reduced and can cause
increased forward head posture. This is in agreement with
another study showing that increased forward head pos-
ture during VDU work caused an increase in the muscular
activity in the neck–shoulder musculature to hold the head
and neck in this position, which may then result in muscle
fatigue and muscle imbalance [15]. In addition, this present
study chose the protocol of adding a 3-min rest break after
every 20-min interval because a previous study showed this
to have a favourable effect on avoiding neck and shoulder
muscle fatigue among symptomatic VDU operators [47].
4.5. Limitation
In this study, the effect of rest-break intervention during
a 1-h typing task was investigated in the laboratory set-
ting. Variability over longer periods of times such as shifts,
whole days, from day to day and field studies should also
be examined. The effects of rest-break interventions on
and shoulder posture reported here were for symptomatic
female VDU operators aged 26–31 years on average. Fur-
ther work should investigate whether the variation found
in this group is similar to that found in healthy or older
operators.
5. Conclusion
There were no significant differences among the rest-break
interventions on neck and shoulder posture. However,
stretching and dynamic contraction showed a greater trend
towards a positive effect on CV and FS angles for symp-
tomatic female VDU operators during prolonged computer
typing tasks. In addition, a 3-min rest-break intervention
for every 20 min of VDU work was shown to have posi-
tive effect on the neck–shoulder posture of the symptomatic
operators.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
Financial support for this study was provided by Chulalongkorn
University Centenary Academic Development Projects [#12].
Note
1. Trial registration: UMIN-CTR =UMIN000008385.
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