Muscular, visual and proprioceptive outcomes of computer work with one versus two computer
monitors
Amanda Marlen Farias Zuniga
Department of Kinesiology and Physical Education
McGill University
Montreal, Quebec, Canada
October, 2015
A thesis submitted to McGill University in partial fulfillment of the requirements for the degree
of Master of Science
© Amanda Farias Zuniga, 2015
For my grandparents,
Tata Willy, Abuela, Mama Rosita, and Tata Raul
II
CONTRIBUTION OF AUTHORS
Amanda Farias, the candidate, was responsible for the research, design, setup,
recruitment, data collection, analysis, writing and any other steps related to the completion of the
research study and submission of the thesis as per McGill University requirements.
Julie N. Côté, PhD, Associate Professor, Department of Kinesiology and Physical
Education, McGill University, the candidate’s supervisor, was actively involved in every step
and decision made regarding the research study and the completion of this thesis.
David Pearsall, PhD, Associate Professor, Department of Kinesiology and Physical
Education, McGill University, and André Plamondon, PhD, IRSST, were members of the
candidate’s supervisory committee and contributed to the design of the research protocol.
Kim Emery, MSc, and Larissa Fedorowich, MSc, assisted in the training of the candidate
and provided guidance during the data collection and analysis.
William Franquet, BSc, and Paul Rozakis, BSc, for provided assistance during data
collection and processing.
III
ACKNOWLEDGEMENTS
Firstly, I would like to thank my thesis supervisor, Dr. Julie Côté for helping me reach
this milestone in my life. I am so thankful your guidance, financial and emotional support, and
understanding, both in and out of the lab. Your hard work and dedication is inspiring, and your
commitment to education and research is admirable. Thank you for mentoring me these past few
years and for the relationship we have developed.
To the lab team, thank you for your support, guidance, and most importantly, your
friendship. To the “coach” of the team, Kim Emery, thank you for all your patience in training
and for answering all my questions. Hiram Cantú, I am eternally grateful to you for the
seemingly endless hours your helped me with my set up and MatLab programming. Larissa
Fedorowich, thank you for the guidance and training you provided me throughout these past
couple of years. Zachary Weber, thank you for the many favours you granted me throughout the
years and for your support. William Franquet and Paul Rozakis, thank you both for assisting in
my data collection and analysis, I wish you both the best of luck continuing your studies! And to
the many other OBEL members, both past and present, Adrien Moufflet, Kathryn Sinden,
Michael Yehoyakim, Jonathan Pendenza, thank you for making my experience a positive and
fulfilling one.
Thank you to all the members of the Jewish Rehabilitation Hospital and to all the staff,
Professors, and colleagues at the Department of Kinesiology and Physical Education at McGill
who contributed to my project in any way, shape or form. Thank you to all those who graciously
agreed to participated in my study. Thank you to Dr. David Pearsall and Dr. Plamodon, who
served on my advisory committee, for providing me with your knowledge, insight and
constructive criticism to strengthen this project.
To all the friends I have made over the past 6 years here in Montreal, thank you for your
endless support and encouragement, and for the best years of my life. Thank you Rhea for
taking the time to read my thesis and assist me with the editing process. Special thank you goes
to all my friends and family in Toronto: to my best friends Alessia and Sofia, thank you for
supporting me through the years and always being there when I needed you the most. Mom and
Dad, thank you for all the sacrifices you’ve made, for your unconditional love and support, for
IV
teaching me the value of hard work, and for giving me the freedom to chase my dreams and
achieve my goals. To my brother, Paulo, thank you for always making me laugh and for
reminding me to take things easy. Finally, a special and important thank you to my boyfriend,
Clement Chuong. Clem, thank you for being my rock, for believing in me when I doubted
myself, supporting my goals, celebrating my accomplishments, and encouraging me to chase my
dreams.
V
ABSTRACT
The aim of this Master’s study was to quantify the effects of performing a 90min
computer task with two monitors (DualMon), compared to with one (SingleMon), on
neck/shoulder patterns in healthy young adult males and females. Upper body muscle activity
(EMG) and visual strain were recorded every 9 minutes during a standardized computer task
during two sessions presented in random order. Neck proprioception was also measured before
and after the task. Visual strain increased with time in both workstations in both genders.
Results revealed significant increases in visual strain and Right Upper Trapezius muscle activity
over time. Right Cervical Erector Spinae muscle activity and cervical muscle connectivity was
lower, and degrees of overshoot and end position errors were higher in the DualMon condition.
Additionally, the effects of muscle activity were more pronounced in males, while effects of
proprioception were more pronounced in females. Overall, there was lower and more variable
and bilaterally independent neck muscle activation in DualMon, as well as more overshoot and
relocation error. These results reflect potentially healthier muscular and proprioceptive
responses to computer work with two monitors, and provide evidence to consider when deciding
on the use of dual monitor workstations.
VI
RÉSUMÉ
L'objectif de cette étude de maitrise était de quantifier les effets d’une tâche de 90
minutes à l’ordinateur avec deux écrans en comparaison avec un seul écran sur les patrons
cou/épaules de jeunes adultes masculins et féminins. L'activité musculaire du haut du corps ainsi
que l'effort visuel étaient enregistrés toutes les 9 minutes durant la tâche standardisée à
l’ordinateur pendant deux séances présentées en ordre aléatoire. La proprioception du cou était
aussi mesurée avant et après la tâche. Les résultats ont révélé un augmentation de l'effort visuel
ainsi que de l'activité musculaire du Trapèze Supérieur Droit avec le temps. L'activité musculaire
de l'Érecteur du Rachis Droit, ainsi que la connectivité entre les muscles cervicaux étaient plus
bas et les erreurs de proprioception (degrés de surestimation/erreur de position finale) étaient
plus grande dans la condition à deux moniteurs. De plus, les effets reliés à l'activité musculaire
étaient plus prononcés chez les hommes, tandis que les effets reliés à la proprioception étaient
plus prononcés chez les femmes. Il y avait une plus faible, plus variable et bilatéralement
indépendante activation des muscles du cou avec deux écrans, surtout chez les homes, ainsi que
plus d’erreur de proprioception, surtout chez les femmes. Ces résultats reflètent potentiellement
des réponses musculaires et proprioceptives plus saines lors du travail à l’ordinateur avec deux
écrans et fournissent des preuves à prendre en compte lors d'une décision quant à l'utilisation de
deux écrans à une station de travail.
VII
TABLE OF CONTENTS
CONTRIBUTION OF AUTHORS............................................................................................III
ACKNOWLEDGEMENTS........................................................................................................IV
ABSTRACT…………………………………………………………………………………….VI
RÉSUMÉ……………………………………………………………………………………….VII
INTRODUCTION……………………………………………………………………………….1
LITERATURE REVIEW……………………………………………………………………….3
Neuromuscular Aspects of Neck/Shoulder MSD ………………………………………….3
Vascular & Postural Aspects of Neck/Shoulder MSD …………………………………....5
Computer Vision Syndrome ……………………………………………………………....7
Gender Differences ……………………………………………………………………….8
Single vs. Multiple Monitor Work ………………………………………………………...9
RESEARCH ARTICLE……………………………………………………………………......11
ABSTRACT ………………………………...…………………………………………..12
1. Introduction ………………………………………………………………………...13
2. Methods ……………………………………………………………………………..16
2.1 Participants ……………………………………………………………………...16
2.2 Instrumentation ……………………………………….…………………………16
2.3 Initial Measures………………………………………………………………….17
2.4 Computer Task …………………………………………………………………..18
2.5 Data Analysis…………………………………………………………………….19
2.6 Statistical Analysis ………………………………………………………………20
3. Results……………………………………………………………………………….21
3.1 Visual Strain …………………………………………………………………….21
3.2 EMG ……………………………………………………………………………..21
3.3 Head Repositioning ……………………………………………………………...28
4. Discussion…………………………………………………………………………...31
Acknowledgements……………………………………………………………………..35
CONCLUSION…………………………………………………………………………………36
VIII
REFERENCES………………………………………………………………………………….38
APPENDICES ………………………………………………………………………………….46
A. Consent Form (English Version) ……………………………………………………46
B. Consent Form (French Version) .................................................................................53
IX
INTRODUCTION
Since the Industrial Revolution, Western society has become increasingly reliant on the
use of machines. Furthermore, since the popularization of data-processing devices, such as
computers and handheld devices, new work postures and fine motor movements have been
adopted by workers, predominately by those who work in office environments. As a result,
work-related Musculoskeletal Disorders (WMSDs) have become increasingly prevalent in the
past few decades, especially in occupations involving static low loads and repetitive actions
(Madeleine, 2010). The most frequently reported areas of concern include the neck and
shoulders (Szeto, Straker, & O'Sullivan, 2005a; Woods, 2005). In 2003, Statistics Canada
reported that approximately one in ten Canadian adults had repetitive motion-related MSDs that
were serious enough to limit their daily life activities, and that most were caused by work-related
activities (55%). Moreover, these statistics also report that most of these repetitive injuries affect
the upper body, with the neck and shoulder comprising 25%, followed by wrist or hand injuries
at 23% (StatisticsCanada, 2003). For employees, these limiting injuries mean more time away
from work and lower productivity. In addition, MSDs place a significant burden on Quebec’s
worker compensation board, with more recent studies showing that 38% of all compensated
injuries are related to WMSDs (Chiasson, 2011). Small relative risks of computer use become
important health concerns because of widespread and prolonged computer use (Gerr, Monteilh,
& Marcus, 2006). In fact, in Québec, it has been reported that approximately 21% of workers
use a computer for 31 hours or more per week at their job (Vézina et al., 2011). Furthermore, in
a self-reported questionnaire, Woods (2005) found that 86% of data processors reported
experiencing musculoskeletal discomfort or pain, predominately in the neck region. It is evident
that prolonged computer work significantly impacts neck/shoulder MSD outcomes.
Investigations have identified individual factors, time, exposure level, frequency, and
psychosocial work environment as likely elements of the injury mechanism (Chiu et al., 2002;
Madeleine, Vangsgaard, Hviid Andersen, Ge, & Arendt-Nielsen, 2013). Individual factors
include age and gender, with women reporting higher rates of neck/shoulder symptoms, and with
the prevalence of neck/shoulder tension and pain increasing with age (Chiu et al., 2002; P. Côté
et al., 2008; Madeleine et al., 2013; Polyani et al., 1997). Time or work duration also
1
significantly impacts neck/shoulder symptoms, specifically when Visual Display Unit work
exceeds four hours per day (Bergqvist, Wolgast, Nilsson, & Voss, 1995; Chiu et al., 2002).
Additionally, physical factors that influence neck/shoulder pain include working with a forward
head posture, increased neck flexion, and poor sitting posture (Chiu et al., 2002). Finally,
psychosocial aspects such as job satisfaction, high job demands, and low social support at work
significantly affect WMD development (Chiu et al., 2002; P. Côté et al., 2008).
Research has attempted to uncover underlying mechanisms of MSDs and develop
intervention strategies for their prevention, with limited success, which is thought to be due to a
lack of understanding of the injury mechanisms, on which to base these interventions. In
addition, recently, the use of multiple computer monitors in workplace settings has been an
increasing trend. While these workstations have shown positive outcomes in relation to
workplace productivity and user satisfaction (Kang & Stasko, 2008; Poder, Godbout, &
Bellemare, 2011; Truemper et al., 2008) their effects on musculoskeletal, visual, and
neuromuscular outcomes are largely unknown (Szeto, Chan, Chan, Lai, & Lau, 2014).
Therefore, the objective of this thesis was to quantify the effects of adding a second computer
screen, as well as of working time, on musculoskeletal, visual and neck proprioceptive outcomes
related to neck/shoulder MSDs in healthy young adult men and women. We recruited subjects to
perform a standardized 90min computer task while using two computer screens versus one
screen. We hypothesized that using two computer screens would expose strategies that could be
interpreted as providing some preventative advantages towards the development of computer
related neck/shoulder MSDs when compared to single computer screen use. Our results could
help to gain insight on the mechanism underlying the symptoms associated with prolonged
computer work, and could provide evidence to support or refute the use of alternative computer
work stations.
2
LITERATURE REVIEW
Recent research has provided more insight into the physiological pathways that may lead to or be
associated with the development of MSDs of the neck/shoulder (n/s) region. Among the
hypothesized pathways, we have identified three theoretical models to explain the mechanism of
n/s MSD development.
Neuromuscular Aspects of Neck/Shoulder MSD
Several hypotheses for the development of n/s MSDs exist, with the most widely
recognized being the Cinderella Fiber hypothesis (Hagg, 1991). According to this hypothesis,
type 1 muscle fibers are believed to be at risk of overload since they are active most of the time
in long-lasting low-level activities such as prolonged computer work (Cagnie et al., 2012; Forde,
Punnett, & Wegman, 2002). According to the size principle of motor unit (MU) recruitment, and
since type 1 muscle fibers are associated with the smallest motor units with the lowest
recruitment thresholds, Cinderella fibers are the first ones recruited and remain active for the
longest period of time (Bawa & Murnaghan, 2009; Henneman, 1957). Continuous activation of
these muscle fibers may lead to muscle fatigue due to the accumulation of by-products and Ca2+,
inhibiting muscle relaxation, eventually leading to damage of the fibers themselves (Forde et al.,
2002). This damage ultimately leads to a series of vascular and structural changes within the
muscle fibers, contributing to the onset of discomfort and pain (Visser & van Dieen, 2006).
Evidence supporting the Cinderella hypothesis of MSDs has been debated. Szeto and
colleagues (2005a) explored whether symptomatic subjects had the same muscle activity patterns
as asymptomatic subjects while performing sustained computer work. Their results suggest
higher trapezius muscle activation and deep local muscle inhibition in some cases in
symptomatic subjects. Asymptomatic subjects, on the other hand, kept their muscles more
relaxed, indicating that they may have a more efficient recruitment strategy (Szeto et al., 2005a).
Contrastingly, Strøm et al. (2009) found an association between pain and trapezius blood flow,
but not with muscle activity.
Chronic activation of Cinderella fibers is believed to be a central mechanism in the
development of MSDs. Motor variability, the variation of behavioural outcomes over repetitions
3
or time (Latash, Scholz, & Schoner, 2002), is thereby important in avoiding pain chronicity due
to abnormally high or sustained muscle fiber recruitment. Specifically, it is believed that high
motor variability can prevent the development of chronic symptoms, whereby people who
display more variable activation patterns may use this strategy to switch off the activation of
especially vulnerable muscle fibers, by recruiting other fibers, for instance, in an effort to keep
the overall force level constant (Madeleine, Mathiassen, & Arendt-Nielsen, 2008; Mathiassen,
Moller, & Forsman, 2003). This hypothesis is supported by studies from Madeleine and
colleagues (2008b), where they observed greater motor variability in pain-free workers. Results
from Moseley and Hodges (2006) also support this hypothesis when they observed an
association between larger movement variability and probability of recovering from
experimentally induced pain. Increased variability in response to fatigue is also observed and is
hypothesized to be a healthy fatigue-adaptation mechanism (Fuller, Fung, & Côté, 2011).
Srinivasan and Mathiassen (2012) have further suggested that motor variability provides
direction in understanding and predicting the development of MSDs. However, few studies have
assessed variability during computer work. Most notably, a recent study by Fedorowich and
colleagues (2015) assessed variability during a 90-minute computer-typing task in two different
postures (walking and sitting) and found 65% higher variability in the lower trapezius muscle in
the walking condition compared to sitting. The authors suggested that the higher lower trapezius
variability could represent a shoulder injury protective advantage of the walk-and-work task over
traditional seated computer work (Fedorowich, Emery, & Côté, 2015). To our knowledge, no
other studies have assessed variability during computer work.
Multi-muscle co-activation is also believed to be associated with MSD development, as it
is believed to be an attempt to stabilize and protect a vulnerable body area from further damage
(Lund & Donga, 1991). It is suggested that this mechanism is largely causal, as findings from
recent studies show that elevated low-back co-activation in initially asymptomatic subjects leads
to low-back pain symptoms in these individuals (Gregory & Callaghan, 2008). A computational
technique recently adapted to the study of electromyographical patterns by Madeleine and
colleagues (2011) quantifies the amount of mutual information between the electromyographic
time series of two muscles, accounting for both linear and non-linear signal characteristics,
4
assuming that high levels of mutual information outline functional connectivity between both
muscles. In that study, they found higher connectivity with pain due to delayed onset muscle
soreness, suggesting an association between pain and connectivity. Later, Johansen and
colleagues (2012) used this technique to measure the amount of functional connectivity between
different parts of the trapezius muscle in asymptomatic men and women. Although they found
no effect of task time, they observed that women had higher levels of functional connectivity
(Johansen, Samani, Antle, Côté, & Madeleine, 2012). In the only known study that measured
functional connectivity during computer work, Fedorowich et al. (2015) measured increased
functional connectivity with time for the cervical erector spinae-anterior deltoid pair and for the
cervical erector spinae – lower trapezius pair. Together, these studies suggest that elevated
functional connectivity could reflect the presence of symptoms, although the exact relationship
between functional connectivity and MSD mechanisms still remains unclear.
Vascular and postural aspects of neck/shoulder MSDs
Several hypotheses suggest that MSD symptoms may be associated with factors related to
the underlying vascular physiology. It has been hypothesized that metabolic and morphological
changes in vascular structures within the muscles lead to inappropriate responses (Brunnekreef,
Oosterhof, Thijssen, Colier, & van Uden, 2006; Cagnie et al., 2012). This indeed appears to
occur as Cagnie and colleagues (2012) observed decreased oxygenation of all three parts of the
trapezius muscle during computer work in patients with n/s discomfort, but Strøm and colleagues
(2009) reported contrasting findings in subjects with chronic n/s pain. Although it is well known
that blood flow is important in the oxygenation and repair of active muscles, the relationship
between blood flow and MSDs is not well established.
One of the most significant factors leading to neck/shoulder MSDs is poor and-or static
posture, especially during computer work (Dowler, Kappes, Fenaughty, & Pemberton, 2001;
Szeto et al., 2014). A widely accepted theory for the association between the development of n/s
MSDs and posture is related to elevated neck flexion, which could prevent both optimal
neuromuscular and blood flow mechanisms from ensuring the health of muscles. Previous
studies have found that forward head posture and neck flexion are significantly associated with
5
increased neck pain, and that neck pain increases with increasing neck flexion (Szeto, Straker, &
O'Sullivan, 2005b). It has even been suggested that neck flexion angles of approximately 5˚ can
impact neck movements and forces required to support the weight of the head (Szeto et al.,
2005b). Forward head flexion affects n/s muscles, specifically the upper trapezius, increasing
spasm frequency and area (Chiu et al., 2002). Increased forward head flexion is often
characterized by “slump sitting” or the “poking chin” posture observed between the cervical and
thoracic area of the spine (Caneiro et al., 2010; Chiu et al., 2002), which leads to greater anterior
translation of the head, resulting in a greater moment arm of the head with respect to the axis of
rotation located in the cervical spine (Caneiro et al., 2010). This posture affects surrounding
muscles by increasing the load on posterior neck muscles, inducing muscle fatigue and tension at
these sites (Caneiro et al., 2010; Chiu et al., 2002; Szeto et al., 2005b). Studies by Falla et al.
(2007) and Szeto et al. (2005) have found that individuals suffering from chronic neck pain
display greater neck (cervical) and thoracic flexion.
Poor posture such as the common “poking chin” posture is especially prevalent in
computer work environments, where individuals are often distracted with their work, leading
them to drift to these forward neck postures (Falla, Jull, Russell, Vicenzino, & Hodges, 2007).
More alarmingly, increased forward head postures can gradually develop into a postural habit,
leading to more neck pain and damage to surrounding supporting structures (Szeto et al., 2005b).
This evidence raises the question if workers are aware of this postural habit or not, pointing to a
possibly important role of proprioception in ensuring proper neck posture.
Neck proprioception is an important component of overall neck health, contributing to
correct head-in-space and trunk orientation, body orientation, and balance and control
(Malmstrom, Westergren, Fransson, Karlberg, & Magnusson, 2013). The integrity of cervical
afferent structures is also known to contribute greatly to the control of gait and posture (Pinsault
et al., 2008). It is therefore reasonable to believe that impairment of neuromuscular structures in
the neck area can compromise balance and control of the head. For example, Kristjansson and
colleagues’ (2003) investigation of relocation accuracy in subjects experiencing neck pain due to
whiplash or to insidious onset found that whiplash subjects demonstrated higher number of
relocation errors than insidious onset counterparts. However, neck proprioception in relation to
6
prolonged computer work has, to our knowledge, not been investigated. As a result, the potential
influence of static, prolonged computer work on neck proprioceptive structures is largely
unknown.
Although no gold standard test is currently available, the Cerviocephalic Relocation Test
(CRT) to neutral head position (NHP) is a test that has been used in a number of studies
(Armstrong, McNair, & Williams, 2005; Malmstrom et al., 2010; Malmstrom et al., 2013) to
assess neck proprioception through measurements of head relocation accuracy and overshoot.
Administration of this test requires the subject to be blindfolded and seated on a chair with their
head in the NHP. They are then asked to move their head fully either to the left or right side, and
to come back as accurately as possible to the NHP. This process is carried out for between 8-10
trials to ensure good to excellent reliability (Pinsault et al., 2008). Results from some
investigations using this test suggest that muscle fatigue and tension, along with central nervous
system changes, may modify neck sensorimotor control, and that pain interferes with muscle
activity or adaptation in movement strategy (Malmstrom et al., 2013).
Computer Vision Syndrome
In addition to proprioception, vision is also commonly known as a sensory submodality
linked to neuromuscular control. However, computer users commonly experience eye fatigue
and strain, especially when using computers for extended periods of time. This is collectively
referred to as “computer vision syndrome”, and is specifically characterized as an ensemble of,
“symptoms of eye strain, tired eyes, irritation, burning sensation, redness, blurred vision and
double vision” (Blehm, Vishnu, Khattak, Mitra, & Yee, 2005). Computer vision syndrome
(CVS) can also include non-ocular symptoms such as headaches, neck, shoulder and back pain,
and nausea (Blehm et al., 2005; Lie & Watten, 1994). These symptoms are often considered to
be transient and reversible (Wolkoff, Skov, Franck, & Petersen, 2003) as they usually disappear
after computer work is complete. Moreover, it has been reported that the symptom prevalence of
eye irritation for both men and women is between 25-40% in North America and Europe
(Wolkoff et al., 2003), and that eyestrain can peak as high as 76 ± 20mm on a 100mm scale
during a 90-minute office work task (Strøm, Røe, & Knardahl, 2009).
7
Visual strain has also been shown to influence neck/shoulder muscle activity, further
influencing the prevalence of neck-shoulder tension and pain (Zetterberg, Forsman, & Richter,
2013). The theory behind this interaction is two part; first it is believed that eye-lens
accommodation through ciliary muscle activity mediates the mechanism behind increased
trapezius muscle activity. Secondly, incongruence between the accommodation and congruence
of the eye gives rise to increased trapezius activation. To test these hypotheses, Zetterberg and
colleagues (2013) investigated thirty-three participants with neck pain while performing a
standardized vision task four times, each with different lenses mounted on different frames.
While their results did not support the first hypothesis, they did provide some evidence
supporting the second. It was also found that the presence of neck/shoulder discomfort did not
affect trapezius muscle activity during these tasks. From these results, Zetterberg and colleagues
(2013) believe that incongruence between accommodation and convergence of the eyes are
largely involved in influencing trapezius muscle activity. Therefore, a good understanding of the
computer work-related n/s mechanisms may be linked to the understanding of how computer
work affects eye strain.
Gender Differences
Higher instances and prevalence of work related neck/shoulder pain in women is
commonly reported (J. N. Côté, 2012). It has been noted that women suffer approximately twice
as much as men from work related musculoskeletal complaints of the neck and upper extremities
(Nordander et al., 2008). Biological and physiological differences between the sexes have been
previously speculated as a possible source for differences in injury mechanisms among the sexes
(J. N. Côté, 2012). Indeed, several studies have noted sex differences in muscle activity patterns,
visual symptoms, and position sense. For instance, higher prevalence of eye irritation and dry
eyes has been reported in females (Blehm et al., 2005; Wolkoff et al., 2003). Differences in
muscular strategies between the sexes have also been noted, most of which suggest that women
display unfavourable patterns. Women have shown more activation of accessory muscles and
less activation of primary muscle groups compared to men (Anders, Bretschneider, Bernsdorf,
Erler, & Schneider, 2004), as well as higher connectivity between muscle pairs, suggesting
8
differing movement strategies and fatigue adaptation mechanisms (Fedorowich, Emery, Gervasi,
& Côté, 2013; Johansen et al., 2012). Higher activation levels of the upper trapezius muscle in
females has also been observed, an unfavourable pattern as it may contribute to overloading of a
muscle known to be prone to WMSDs (Johansen et al., 2012). Although sex differences in
muscular activation are reported, authors caution that these responses seem to be task specific
(Emery & Côté, 2012). Current studies have not assessed sex differences in n/s proprioception in
response to computer work, however sex differences have been noted in head-neck stabilization
responses to external forces. An investigation by Tierney and colleagues (2005) observed sex
differences in head-neck segment dynamic stabilisation during head acceleration in response to
an external force, where women showed greater displacement compared to males. Overall, it
appears that neck/shoulder neuromuscular, proprioceptive and visual differences exist between
the sexes, although no clear, overall distinction between these patterns of males and females has
been reached.
Single Vs. Multiple Monitor Work
Recent improvements in computer technology have both simplified and complicated
tasks for workers. While multiple monitor set-ups can help with the problems that come with
using small monitors, they simultaneously present new problems with managing this extra space
(Hutchings, Smith, & Meyers, 2004). Even though multiple monitor, or “multimon”
(Czerwinski et al., 2003) displays have been used for approximately 20 years, their use has been
primarily restricted to financial traders, graphic designers, and software developers (Truemper et
al., 2008). “Multimon” refers to dual or multiple monitors that treat displays as a single
continuous space so that objects can be moved from one monitor to the next (Grudin, 2001).
Only recently have these multimon set-ups become common in office work environments,
primarily due to advancements in graphic cards (Czerwinski et al., 2003).
In spite of current restrictions with dual monitor use, the use of multimon displays in
demanding environments has shown to increase productivity and efficiency. A recent study
conducted in the Archiving Department of a Canadian hospital reported that archivists’
processing times were about a minute faster per case when using a dual monitor set-up,
9
amounting to potential cost savings of $154 585 CAD over 5 year per dual-monitor workstation
(Poder et al., 2011). Kang & Stasko (2008) also found reduced overall task times among
multimon users. However, studies by Stegman, Ling & Shehab (2011) and Truemper and
colleagues (2008) found no significant differences in task completion times. Interestingly,
although Kang & Stasko (2008) observed increased productivity (lower task completion time) in
the multimon setting, they found that the advantages of multimon over singlemon decreased as
the user became more familiar with the task.
Evidence supporting the use of multimon workstations from a musculoskeletal health
standpoint has been largely absent. Two main studies emerge in this area of investigation, one by
Nimbarte and colleagues (2013) and more recently by Szeto and colleagues (2014). Nimbarte et
al. (2013) investigated changes in muscle activity and head-neck posture during a 25-minute
computer task, and found that the activity of the right sternocleidomastoid was significantly
greater in the dual-monitor layout, and that activity of the cervical muscles were not significantly
affected by monitor layout. Contrastingly, Szeto and colleagues (2014) observed significant
reductions in the 50th and 90th percentiles of APDF (amplitude probability distribution function),
especially for the right upper trapezius muscles, during a fifteen-minute standardized computer
tasks. These seemingly contrasting findings could be influenced by the different tasks and
positioning of the computer screens and devices in each study, suggesting that computer monitor,
accessory placement and tasks can play a role in neck musculature patterns in dualmon stations.
Although muscular responses to dual-monitor work have not be established, it has been
suggested that using two screens may require more frequent head movements and may therefore
be associated with greater variation in muscle activity, possibly providing some protection
against the development of n/s MSDs (Szeto et al., 2014). This, however, requires further
investigation.
10
RESEARCH ARTICLE
Effects of dual monitor workstation on neck-shoulder muscular and proprioceptive
characteristics associated with a 90-minute computer task in males and females
Amanda M. Farias Zuniga1, Julie N. Côté1
1. Department of Kinesiology and Physical Education, McGill University, 475 Pine Avenue
West, Montreal, Quebec, H2W 1S4, Canada; Feil & Oberfeld/CRIR Research Center,
Jewish Rehabilitation Hospital, 3205 Alton Goldbloom Place, Laval, Quebec, H7V 1R2,
Canada
In preparation, for submission to Human Factors: The Journal of the Human Factors Society
11
ABSTRACT
Objective: The effects of performing a 90-min computer task with a single monitor versus a dual
monitor workstation were investigated in healthy young male and female adults. Background:
Work-related musculoskeletal disorders (WMSDs) are common among computer (especially
female) workers. Although working with multiple monitors has become popular, few studies
have provided objective evidence on how this affects the musculoskeletal system in both
genders. Methods: 27 healthy participants (mean age= 24.6 years; 13 males) completed a 90minute computer task while using a single monitor (SingleMon) or dual monitor (DualMon)
workstation. Electromyography (EMG) from eight upper body muscles, and visual strain using a
visual analog scale (VAS) were measured throughout the task. Neck proprioception was tested
before and after the computer task using a head-repositioning test. EMG amplitude (RMS),
variability (CoV), normalized mutual information (NMI), and head repositioning overshoot and
accuracy were computed. Results: Visual strain (p < .00) and Right Upper Trapezius RMS (p
=.03) increased significantly over time. Right Cervical Erector Spinae RMS and cervical NMI
were found to be lower, while degrees of overshoot (mean = 4.15˚) and end position error (mean
= 1.26˚) were observed to be higher in DualMon. Effects on muscle activity were more
pronounced in males, whereas effects on proprioception were more pronounced in females.
Conclusion: Results suggest that DualMon work is effective in reducing cervical muscle activity,
dissociating cervical connectivity, and maintaining more typical neck repositioning patterns,
suggesting some health protective effects. Application: This evidence could be considered when
deciding on computer workstation designs.
12
1. Introduction
Work-related musculoskeletal disorders (WMSDs) are particularly common in occupations
involving static low loads and repetitive actions (Madeleine, Voigt, & Mathiassen, 2008), two
characteristics of computer work. Among the affected areas, the most frequently reported
include the neck and shoulder (n/s) (Madeleine, Voigt, et al., 2008; Szeto et al., 2005a; Woods,
2005). In 2003, upper extremity disorders accounted for 14.2% of lost time claims in Canadian
workers (WSIB, 2014). In addition, generally higher instances and prevalence of n/s WMSDs
are reported in women (J. N. Côté, 2012). Although risk factors in the development of n/s
WMSDs have been identified, the injury mechanisms underlying this chronic disease are still
poorly understood.
Although computer work does not require large amounts of muscle activity, prolonged
computer use is increasingly associated with adverse health effects and to physical risk factors
which ultimately contribute to MSDs (Szeto et al., 2014). Previous studies have presented
conflicting reports on the association between patterns of muscle activity amplitude in the n/s
region and musculoskeletal pain or discomfort (Madeleine, 2010; Strom, Roe, & Knardahl, 2009;
G. P. Szeto et al., 2005a), suggesting the need for other methods to analyse muscle activity
patterns. One such method is to investigate motor variability (MV), which has been defined as
the inherent variability in motor actions (Latash et al., 2002). Studies have reported lower MV in
individuals with chronic n/s pain during simulated cutting tasks (Madeleine, Voigt, et al., 2008)
and during repetitive pointing (Lomond & Côté, 2010). Conversely, greater MV has been found
in healthy populations in response to fatigue (Fuller et al., 2011) and acute pain (Madeleine,
Voigt, et al., 2008). In fact, several studies have suggested that MV may positively mitigate
fatigue development (Fuller et al., 2011) and potentially protect workers from WMSDs
(Madeleine, Voigt, et al., 2008). However, few studies have assessed MV during computer work.
Recently, Fedorowich et al., (2015) assessed MV during a 90-minute computer-typing task in
two different postures (walking and sitting). They notably found 65% higher variability in the
lower trapezius (LT) muscle in the walking posture compared to the sitting posture, and
suggested that greater LT MV could represent a shoulder injury protective advantage of the
13
walk-and-work task over the traditional seated computer work posture (Fedorowich et al., 2015).
To our knowledge, no other studies have assessed MV during computer work.
The way that muscles work together is also believed to be associated with MSD
development. Mutual Information (MI), a computational technique recently applied to muscle
activity signals, allows for the investigation of shared information between two time series
(Johansen et al., 2012). Previous studies have suggested that higher MI may represent a
suboptimal strategy and increase the risk of developing MSDs, a pattern which has been
observed more frequently in women (Johansen et al., 2012). In addition, the Fedorowich et al.
(2015) study also reported increased connectivity with time between the cervical erector spinae
and two other shoulder muscles during a 90-min computer work task, suggesting an association
between increased connectivity and time-related development of discomfort. However, no
studies have assessed whether modifying cervical posture or movement during computer work
has an impact on muscular mutual information outcomes.
Prolonged and static work posture, as seen during computer work, has been identified as
one of the major risk factors for n/s WMSDs (Bergqvist et al., 1995; Gerr, Marcus, & Monteilh,
2004; Szeto et al., 2014). A systematic review by P. Côté et al. (2008) found that working in
prolonged, sedentary positions increased the risk of neck pain more than two fold in some
workers. Prolonged static contractions, such as those that may be experienced during static
computer work, has also been suggested to change motion perception and cause a sensory
mismatch in some situations (Malmstrom et al., 2010). In a study by Malmstrom and colleagues
(2010), the normal overshoot response observed during a standardized head repositioning task
was reduced after a five-minute, low-force contraction in healthy participants (Malmstrom et al.,
2010), suggesting that low-force contractions can alter neck proprioception. Previous studies
have also found that forward head posture and/or neck flexion is significantly associated with
higher upper trapezius activity in symptomatic office workers (Szeto et al., 2005b). Increased
forward head postures may gradually develop into a postural habit (Szeto et al., 2005b),
potentially damaging supporting structures and associated neck proprioceptive elements,
compromising the control of the head. Although current studies have not assessed gender
differences in the n/s proprioception in response to computer work, gender differences have been
14
noted in head-neck stabilization responses to external forces, where females displayed
significantly greater head-neck segment peak angular acceleration and displacement when
compared to males, despite activating neck muscles earlier and at a greater percent of their
maximum (Tierney et al., 2005).
Prolonged computer use is also associated with various ocular symptoms, often
collectively referred to as “computer vision syndrome” (CVS) (Blehm et al., 2005; Lie &
Watten, 1994). Although these eye symptoms are usually temporary, symptom prevalence of eye
irritation is between 25-40% in North America and Europe (Wolkoff et al., 2003), and is higher
in women (Blehm et al., 2005; Wolkoff et al., 2003). Notably, eyestrain has also been associated
with changes in trapezius muscle activity, which could reflect a role of eyestrain in the
development of n/s MSD (Zetterberg et al., 2013).
Multiple computer monitor workstations have been gaining in popularity, and studies
show benefits in terms of productivity and user satisfaction (Kang & Stasko, 2008; Owens et al.,
2012; Poder et al., 2011; Truemper et al., 2008). However, few investigations have provided data
to objectively determine how they affect exposure to n/s MSD. Nimbarte and colleagues (2013)
found significant increases in head-neck rotation and activity of the right sternocleidomastoid in
dual monitor screen layouts, and Szeto’s et al. (2014) found significant reductions in both 50th%
amplitude probability distribution function (APDF) and APDF range values for the right upper
trapezius. It has been suggested that using two screens may require more frequent head
movements, and therefore be associated with greater variation in muscle activity, possibly
providing some protection against the development of n/s MSDs (Szeto et al., 2014). However,
this relationship has yet to be established.
The objective of the present study was to quantitatively compare the effects of a
standardized 90-minute computer task using a single monitor workstation versus a dual monitor
workstation on muscular outcomes, as well as on neck proprioception/position sense and visual
strain in males and females. We hypothesized that the dual monitor workstation would reveal
beneficial muscular strategies, better neck position sense, and less visual strain, and that there
would be gender differences related to these outcomes.
15
2. Methods
2.1 Participants
A convenience sample of 27 healthy young adults (13 males, 14 females; mean age= 24.6
years; mean height= 171.9 cm; mean mass= 60.7 kg) was recruited by the researchers from the
institutional social network. This choice of sample size is based on calculations from data
reported by Strøm and colleagues (2009) who included 24 participants, which yielded effect
sizes of 2 for trapezius EMG amplitude for time comparisons. Additionally, this genderbalanced sample allowed us to compute gender comparisons on the data. The inclusion criteria
were: use of a computer for more than 40 hours per week (not exclusively dual-monitor use),
between 20 to 35 years old; volunteer to participate in two experimental sessions; free of history
of neurological or musculoskeletal injuries to the neck, shoulder or back or eye injuries, or any
other general health concerns assessed by using a Par-Q Health Questionnaire; normal or
corrected vision (excluding bifocal lenses). The study was performed at the Occupational
Biomechanics and Ergonomics Laboratory (OBEL) of the Jewish Rehabilitation Hospital (JRH)
in Laval, Quebec. Informed, written consent was obtained from all participants, by signing
forms approved by the Research Ethics Board of the Center for Interdisciplinary Research in
Rehabilitation (CRIR) of Greater Montreal.
2.2 Instrumentation
The participant was fitted with EMG equipment (TeleMyo, Noraxon, USA, 10-350 Hz
operating bandwidth) using bipolar Ag/AgCl surface electrodes at eight muscle sites. Electrodes
were placed at the following sites in accordance with recommendations from Basmajian &
Blumenstein (1980): bilaterally on the cervical erector spinae (RCES, LCES) and the
sternocleidomastoid (RSCM, LSCM), and unilaterally (dominant, i.e. right side) on the upper,
middle and lower trapezius ((RUT, RMT, RLT) and anterior deltoid (RAD). A ground electrode
was placed over the seventh cervical vertebrae. EMG electrodes and cables were further fixed
onto the participant’s skin with medical tape to reduce cable movement. EMG data was sampled
at 1000 Hz.
16
To collect kinematic data, passive reflective markers were placed over anatomical
landmarks in accordance with an upper body version of the Plug-In-Gait marker set (Lomond
and Côté, 2010). Kinematics of the head, neck, shoulder, arm and trunk was recorded using a
high-resolution 6-camera Vicon MX3 motion analysis system (Vicon Peak, UK) sampled at
100Hz.
Figure 1 Rear view of subject outfitted with EMG electrodes and kinematic markers. Subject is
in the single computer monitor workstation.
2.3 Initial Measures
Baseline neck position sense measures were taken using the cervicocephalic relocation
test (CRT) (described in Malmstrom et al., 2013; Pinsault et al., 2008). The test was performed
17
eight times rotating to the right, and eight times rotating to the left (Pinsault et al., 2008). No
feedback was given to the participants about their relocation performance at any point in the test.
The participant then completed a series of maximum voluntary isometric contractions
(MVIC) and submaximal reference isometric voluntary contractions (RVIC).An RIVC of the
RUT was obtained by having the participants hold both arms straight and horizontal for 15
seconds at 90˚ abduction in the frontal plane, with their palms facing downward. For the RAD
RIVC, participants held their arms straight and horizontal in the sagittal plane for 15 seconds,
with their arms abducted at 90˚ and their palms facing downward (Mathiassen, Winkel, & Hägg,
1995). MVICs of the RMT, RLT, RCES and LCES were performed as described by Fedorowich
and colleagues (2015). An MIVC was performed for the RMT, where the participant performed
scapular adduction with their arms supported at a 90˚ angle. An MIVC was also obtained from
the RLT and consisted of scapular depression, their arms straight and horizontal at an angle of
90˚, pushing down against resistance. To obtain MIVCs for the RCES and LCES, subjects laid
prone on a table (head unsupported) and performed neck extension against manual resistance
applied on the posterior aspect of the head (Fedorowich, Emery & Cote, 2015). Finally, to
obtain MVIC values for the RSCM and LSCM, participants laid supine on a table (head
supported) and performed anterolateral neck flexion against manual resistance applied on the
temporal region of the head (Kendall, McCreary, & Kendall, 1993). For MVICs, two ramp-up,
ramp-down, five-second trials were performed for each muscle with verbal encouragement to
contract their muscles and push against the resistance as hard as possible. For both MVICs and
RVICs, one minute of rest was given between each of the trials.
After baseline measures were obtained, the participant was seated, and the computer
monitor(s), keyboard, and chair were adjusted according to the individual’s posture and standard
ergonomic recommendations (Occupational Health Clinics for Ontario Workers, 2008; Workers’
Compensation Board- Alberta, 2007) for each of the dual monitor (DualMon) and single monitor
(SingleMon) sessions, which were assigned in random order and spaced two to seven days apart.
A single laptop was used for the SingleMon session as laptop use is very common in various
workplace settings due to its portability and feasibility. In the DualMon session, two monitors of
similar size and resolution were placed side by side, centered to the participant and angled
18
inward at approximately 160˚ (Figure 2). A standard keyboard was placed at the center of the
two monitors (Kang & Stasko, 2008; Poder et al., 2011). This DualMon set-up was chosen
because it is fairly representative of what is found in various office settings and has been
previously used (Kang & Stasko, 2008). A standard external mouse was used with both the
laptop and dual monitor workstation, and was placed to the right side of the keyboard. To begin
each session, the participant was given a five-minute familiarization period. Then, a static
posture trial for EMG and kinematic data was recorded, and baseline visual strain was measured
using a visual analog scale (VAS). The VAS consisted of a 100 mm line, with the numbers “0”
and “10” written at either end of the line. The participant was instructed to make a mark along
the line to indicate the level of visual strain they were experiencing at the moment, with “0”
meaning no visual strain to “10” meaning the worst visual strain imaginable. The visual strain
intensity was scored by measuring (in mm) the distance between zero to where the participant
made the mark (Jensen, Chen, & Brugger, 2003).
Figure 2 Representation of DualMon workstation set-up
19
2.4 Computer Task
The computer task consisted of a 90-minute reading, typing, and search and find
component (Alabdulmohsen, 2011). The text content of the tasks was different in each session
but comparable in terms of complexity. The task required the participant to plan a trip between
two cities (one Canadian and one American city), and involved the use of multiple programs,
including Microsoft Word, Excel and PowerPoint, Adobe Reader, and Internet Explorer. In
DualMon, the types of programs (i.e. Microsoft Word, Powerpoint etc.) were restricted on each
monitor, making it necessary for the participants to complete the task by using both screens
simultaneously. The participant performed the task in ten blocks of nine minutes, with EMG and
kinematic data collection taking place in the last 30 seconds of each block. The participant’s
level of reported visual discomfort was measured after each nine-minute block using the VAS.
At the end of the 90-minute task, the CRT was performed again.
2.5 Data Analysis
EMG data was filtered using a dual-pass 4th-order Butterworth band-pass of 20-500Hz.
Heartbeats were removed from the signals by first identifying a reference heartbeat in one trial,
and then cross-correlating it with the other signals to eliminate heartbeats from all 8 muscle
signals. Signals were then full-wave rectified and normalized to EMG data collected during the
MIVC or RIVC trials. Root-mean-square (RMS) values were calculated over 30 1-s nonoverlapping windows for each collection period and the 30 RMS values were averaged to obtain
one representative mean amplitude value for each muscle from each collection block. Variability
was calculated by computing the coefficients of variation (CV) for each muscle in each block by
dividing the standard deviation of the 30 RMS values by the average RMS value. Finally,
Normalized Mutual Information (NMI), a measure of functional connectivity between two
muscles, was calculated using EMG time series from each block, for which details can be found
in Johansen et al. (2012). Briefly, NMI is based on the Entropy calculation of the EMG time
series, valued between 0, indicating no connectivity, and 1, indicating complete functional
connectivity of the muscle pair. NMI was calculated for all the possible pairs in this study,
calculated over 500-ms window for each trial, with the median value taken to represent the trial.
20
Kinematic data was low-pass filtered (zero-lag second order Butterworth filter, 6 Hz).
Only head position in the frontal plane from the CRT trials were extracted and are presented
here. Two-50 frame windows were taken in each trial with one measuring overshoot and the
other measuring end position error, with overshoot defined as how much the subject
overestimated the initial position, and end position error being how far they were from the initial
position at the end of the trial (Figure 3). Since participants’ individual initial positions varied,
all individual positions were normalized to zero. All the absolute values in degrees from each 50
frame window were averaged separately for left and right rotations, to attain one set of pre-task
values and one set of post-task values for each session and for each side (right or left). All
analyses were done using Matlab software (Mathworks, Massachusetts, USA).
Figure 3 Typical curve for CRT trials of normalized head position (moving to the right) in
degrees over time in milliseconds. Since Participant’s individual starting positions varied, all
individual starting position was normalized to zero. Highlighted areas indicate Overshoot and
End Position Error areas used for analysis, taking 50 frames from each of these areas.
Visual strain results from the Visual Analog Scale were recorded for each of the eleven
time points (one for baseline and one per block) in each condition by measuring the distance, in
21
mm, from the zero line to the mark made by the participant in each trial on the VAS. Descriptive
statistics (group averages and SD) were calculated on this and all other data.
2.6 Statistical Analysis
Two-way repeated measures ANOVA with conditions of Time (10 times, each 9 minute)
and Workstation (two conditions: DualMon, SingleMon) were used to determine main and
interaction effects on RMS and CV per muscle, NMI for every muscle pair combination, and
visual strain (VAS) variables. Changes in head repositioning outcomes were assessed using a
three-way repeated measures ANOVA (Workstation x Time x Side (right or left)). For all
analyses, ANOVAs were calculated first for group averages, and then separately for the genders.
3. Results
3.1 Visual Strain
Results from VAS data revealed significant increases in visual strain over time
independently from the Workstation condition (significant Time effect, [F(10, 260) =
15.68, p <.00], effect size (η2partial) = 0.38), and for each gender when analysed separately
(significant Time effect, Male: [F(10, 120) = 7.94, p = .01], effect size (η2partial) = 0.40;
Female: [F(10, 130) = 8.57, p = .01], effect size (η2partial) = 0.40) (Figure 2).
22
25
Score (mm)
20
15
Single
10
Dual
5
0
0
9
18
27
36
45
54
Time (minutes)
63
72
81
90
Figure 4 Visual Analog Scale scores in millimeters for eye strain over time in both workstations
(group averages, SE). There is a significant time effect (p < .00) with higher visual strain scores
at the end of the task.
3.2 EMG
Analysis of EMG RMS revealed few but some significant effects. RCES RMS was
significantly lower in DualMon (significant Workstation effect, [F(1, 20) = 5.03, p = .04], effect
size (η2partial): 0.20). In addition, RUT RMS significantly increased over time, independently
from workstations (significant Time effect, RUT [F(9,162)= 2.78, p= .03], effect size (η2partial):
0.13). When statistical analyses were performed separately for each gender, significant time
effects were found for both RUT RMS and RAD RMS with increases in males (significant Time
effects, RUT [F(9, 90) = 2.94, p = .04], effect size (η2partial): 0.23; and RAD [F(9, 81) = 3.29, p =
.03], effect size (η2partial): 0.27). No other significant effects were found (Table 1).
23
Table 1. Marginal Means and standard error of muscles with significant EMG RMS results for the group, male and female
participants. No Workstation x Time interaction effects were found.
RUT
T1
T10
RAD
T1
T10
EMG RMS
(%MVIC/
RVIC)
RMT
T1
T10
RLT
RCES
LCES
RSCM
LSCM
Group
10.38
(2.23)
14.85
(2.91)
8.23 (1.97)
10.66
(3.30)
6.97 (3.51)
T1
14.82
(6.82)
2.48 (0.52)
T10
4.36 (1.45)
T1
9.30 (1.74)
T10
T1
10.14
(2.23)
8.96 (1.26)
T10
7.63 (0.89)
T1
9.21 (3.41)
T10
7.76 (2.62)
T1
5.35 (1.54)
T10
4.99 (1.53)
Average (Marginal Means (SE))
Single
Dual
Male
Female
Group
Male
9.53
11.55
11.88
14.23
(2.01)
(4.71)
(2.41)
(3.68)
15.44
14.03
15.89
21.00
(3.73)
(4.93)
(3.73)
(5.66)
9.69
6.60
13.58
8.55
(2.40)
(3.27)
(4.85)
(1.49)
15.48
5.31
14.69
14.98
(5.95)
(0.74)
(3.42)
(3.71)
11.83
2.70
16.17
19.91
(8.41)
(0.63)
(7.44)
(16.00)
26.48
3.09
15.58
15.10
(15.32)
(0.61)
(8.34)
(11.75)
3.22
1.74
3.23
2.49
(0.94)
(0.40)
(0.79)
(0.58)
6.46
2.26
3.11
2.29
(2.77)
(0.42)
(0.78)
(0.61)
8.11
10.61
5.70
5.43
(2.82)
(2.01)
(0.75)
(1.38)
8.21
12.27
6.52
4.16
(3.36)
(2.90)
(1.51)
(1.01)
6.48
11.94
10.14
7.52
(1.30)
(1.97)
(1.72)
(1.65)
7.47
7.82
12.16
8.54
(1.43)
(1.04)
(2.23)
(1.80)
11.72
4.58
7.81
19.12
(5.36)
(3.66)
(2.35)
(9.56)
9.82
3.67
6.90
15.69
(3.73)
(2.88)
(2.31)
(8.61)
4.65
6.12
7.50
8.04
(1.36)
(2.94)
(1.68)
(2.47)
4.88
5.10
6.20
7.51
(1.66)
(2.73)
(1.54)
(2.43)
Female
8.65 (2.50)
Group
.03*
Time main
p
Male
Female
.04*
.05
Workstation main
p
Group
Male
Female
.67
.19
.71
8.86 (3.12)
19.17
(10.08)
14.37
(6.19)
8.92 (5.51)
16.79
(13.46)
4.15 (1.46)
.15
.03*
.49
.53
.31
.14
.40
.34
.39
.48
.59
.39
.50
.36
.36
.88
.13
.13
.42
.28
.37
.04*
.20
.09
.28
.14
.50
.14
.66
.10
.26
.29
.48
.53
.60
.60
.25
.61
.34
.35
.21
.83
3.94 (1.44)
6.00 (0.54)
9.10 (2.83)
13.28
(3.02)
16.49
(4.13)
3.45 (1.88)
3.37 (1.99)
6.91 (2.35)
4.77 (1.86)
The variability of the RMT significantly increased over time (significant Time
effect, RMT [F(9, 198)= 2.36, p = .04], effect size (η2partial): 0.11). When compared by
gender, it was found that male subjects were primarily driving this effect (significant
Time effect, RMT [F(9, 99) = 2.22, p = .03], effect size (η2partial): 0.17), since there was
no significant time effect in females. No significant effects were found for any of the
other variability measures (Table 2).
25
Table 2. Marginal means and standard error of muscles with significant variability results for the group, male and female participants. No
Workstation x Time interaction effects were found.
RUT
RAD
RMT
CoV
RLT
RCES
LCES
RSCM
LSCM
T1
Group
0.44 (0.08)
T10
0.67 (0.09)
T1
0.64 (0.15)
T10
0.98 (0.15)
T1
0.43 (0.09)
T10
0.74 (0.12)
T1
0.73 (0.19)
T10
T1
0.73
(0.110
0.21 (0.03)
T10
0.37 (0.10)
T1
0.21 (0.04)
T10
0.24 (0.04)
T1
0.29 (0.09)
T10
0.30 (0.05)
T1
0.18 (0.04)
T10
0.28 (0.05)
Average (Marginal Means (SE))
Single
Dual
Male
Female
Group
Male
0.42
0.46
0.55
0.47
(0.12)
(0.10)
(0.08)
(0.11)
0.87
0.43
0.63
0.37
(0.11)
(0.10)
(0.12)
(0.08)
0.49
0.63
0.79
0.71
(0.17)
(0.21)
(0.13)
(0.17)
0.92
0.78
0.91
0.57
(0.19)
(0.19)
(0.14)
(0.10)
0.42
0.56
0.51
0.38
(0.10)
(0.15)
(0.10)
(0.08)
0.74
0.69
0.55
0.53
(0.15)
(0.12)
(0.09)
(0.11)
0.95
0.60
0.62
0.78
(0.35)
(0.17)
(0.12)
(0.19)
0.74
0.89
0.77
0.74
(0.13)
(0.23)
(0.16)
(0.24)
0.24
0.18
0.29
0.36
(0.06)
(0.03)
(0.06)
(0.11)
0.37
0.37
0.32
0.36
(0.07)
(0.21)
(0.06)
(0.11)
0.25
0.18
0.27
0.27
(0.06)
(0.03)
(0.04)
(0.06)
0.29
0.18
0.33
0.34
(0.05)
(0.04)
(0.05)
(0.06)
0.23
0.36
0.40
0.42
(0.06)
(0.18)
(0.11)
(0.18)
0.31
0.30
0.36
0.40
(0.08)
(0.07)
(0.08)
(0.14)
0.20
0.16
0.26
0.28
(0.06)
(0.03)
(0.05)
(0.07)
0.27
0.29
0.29
0.24
(0.07)
(0.08)
(0.06)
(0.05)
Female
0.65 (0.13)
Group
0.18
Time main
p
Male
Female
0.32
0.32
Workstation main
p
Group
Male
Female
0.98
0.11
0.09
0.94 (0.21)
0.63 (0.16)
0.42
0.73
0.64
0.42
0.08
0.68
0.04*
0.03*
0.27
0.48
0.1
0.84
0.4
0.71
0.12
0.42
0.8
0.41
0.58
0.71
0.53
0.22
0.76
0.14
0.21
0.13
0.7
0.14
0.56
0.18
0.46
0.46
0.45
0.21
0.14
0.8
0.17
0.35
0.37
0.61
0.52
0.87
1.13 (0.24)
0.53 (0.13)
0.66 (0.12)
0.58 (0.17)
0.78 (0.21)
0.20 (0.03)
0.27 (0.06)
0.27 (0.06)
0.33 (0.09)
0.37 (0.10)
0.30 (0.04)
0.24 (0.06)
0.35 (0.12)
DualMon displayed significantly lower RSCM-RCES and RCES-LCES
connectivity compared to SingleMon (significant Workstation effect, RSCM-RCES [F(1,
24)= 7.39, p = .02], effect size (η2partial): 0.19; RCES-LCES [F(1, 24) = 5.79, p = .01],
effect size (η2partial): 0.24). In males, RUT-RMT and RAD-RCES connectivity increased
significantly over time (significant Time effect, UT-MT: [F(9,108)= 2.17, p = .03], effect
size (η2partial): 0.15; RAD-RCES: [F(9,108)= 3.44, p = .01], effect size (η2partial): 0.22).
Also in males, the adaptation to time differed significantly between the two workstation
conditions in the RMT-RLT muscle pair (significant Workstation x Time effect [F(9,
108) = 2.315, p = .02], effect size (η2partial): 0.16) (Figure 5). No other effects were found
(Table 3).
27
Table 3. Marginal means and standard error for select muscles pairs with significant NMI results for the group, male and female
participants. One Workstation x Time interaction effect was observed in Male participants in the RMT-RLT muscle pair ([F(9, 108)=
2.32, p = .02, η2partial = 0.16)
RUT- RMT
T1
T10
RUT-RCES
T1
T10
RAD-RCES
T1
T10
MI
RMT-RLT
T1
T10
RCES-LCES
T1
T10
RSCM-RCES
T1
T10
RSCM-LSCM
T1
T10
Group
0.029
(0.004)
0.030
(0.004)
0.027
(0.006)
0.034
(0.007)
0.012
(0.002)
0.012
(0.001)
0.020
(0.003)
0.023
(0.003)
0.058
(0.011)
0.058
(0.009)
0.019
(0.003)
0.018
(0.003)
0.065
(0.014)
0.053
(0.012)
Average (Marginal Means (SE))
Single
Dual
Male
Female
Group
Male
0.028
0.030
0.028
0.034
(0.006) (0.007) (0.004) (0.007)
0.034
0.027
0.033
0.040
(0.006) (0.005) (0.005) (0.009)
0.023
0.032
0.022
0.024
(0.007) (0.010) (0.004) (0.007)
0.027
0.042
0.028
0.031
(0.007) (0.013) (0.005) (0.008)
0.010
0.013
0.010
0.010
(0.002) (0.004) (0.001) (0.002)
0.012
0.011
0.011
0.011
(0.002) (0.001) (0.001) (0.002)
0.019
0.022
0.027
0.030
(0.004) (0.006) (0.004) (0.007)
0.027
0.019
0.024
0.022
(0.004) (0.004) (0.003) (0.004)
0.042
0.076
0.038
0.034
(0.013) (0.016) (0.008) (0.010)
0.048
0.069
0.040
0.038
(0.011) (0.015) (0.009) (0.011)
0.013
0.026
0.016
0.012
(0.003) (0.006) (0.002) (0.001)
0.012
0.024
0.015
0.012
(0.002) (0.005) (0.002) (0.002)
0.065
0.066
0.059
0.079
(0.018) (0.022) (0.011) (0.017)
0.051
0.055
0.041
0.058
(0.015) (0.021) (0.009) (0.016)
Female
0.021
(0.004)
0.026
(0.004)
0.021
(0.006)
0.025
(0.007)
0.009
(0.002)
0.011
(0.001)
0.024
(0.005)
0.026
(0.006)
0.042
(0.014)
0.043
(0.014)
0.019
(0.005)
0.018
(0.003)
0.038
(0.011)
0.023
(0.005)
Time main
p
Group
Male
Female
0.23
0.03*
0.78
Workstation main
p
Group
Male
Female
0.88
0.24
0.39
0.15
0.16
0.11
0.06
0.38
0.1
0.23
0.01*
0.38
0.07
0.08
0.37
0.53
0.62
0.73
0.09
0.32
0.19
0.45
0.46
0.37
0.01*
0.02*
0.049*
0.41
0.56
0.22
0.02*
0.15
0.09
0.1
0.2
0.37
0.72
0.4
0.17
0.04
0.035
NMI Indicies
0.03
0.025
0.02
Single
Dual
0.015
0.01
0.005
0
9
18
27
36
45
54
Time (minutes)
63
72
81
90
Figure 5 Functional connectivity between the RMT-RLT muscle pair in male participants in
both workstation conditions over the 90-minute computer task.
3.3 Head Repositioning
DualMon displayed significantly more degrees of overshoot compared to SingleMon
(significant Workstation effect, [F(1,20) = 9.41, p = .01], effect size (η2partial) = 0.32) (Figure 3).
DualMon also showed significantly more degrees of end position error compared to SingleMon
(significant Workstation effect, [F(1,20) = 6.68, p = .02], effect size (η2partial) = 0.25) (Figure 4).
When separated by gender, the overall effect was found to be mainly driven by female subjects.
In females, DualMon showed significantly more overshoot than in SingleMon (significant
Workstation effect, [F(1,11) = 14.48, p = < .00], effect size (η2partial) = 0.57) (Figure 3). When
observing the degrees of end position error in females, significantly more end position error was
found in DualMon when compared to SingleMon (significant Workstation effect, [F(1,11) =
8.25, p = .02], effect size (η2partial) = 0.43)(Figure 4). Additionally in females, the degrees of end
position error remained similar between pre and post-task in SingleMon, while it increased posttask in DualMon (significant Workstation x Time interaction effect, [F(1,11) = 5.07, p = < .05],
effect size (η2partial) = 0.31)(Figure 4). No significant effects were found when analyses were
29
performed specifically on the male subgroup. Additionally, no significant main effects for side
(right or left), or interaction effects with side were found for any of the analyses.
7
Overshoot (degrees)
6
5
4
3
single
2
Dual
1
0
group
male female group
Pre
male female group
post
male female group
pre
male female
post
TO THE R
TO THE L
Time (pre/post) and Side (Right/ Left)
Figure 6. Observed overshoot during the head repositioning test in males and females before and
after 90min of computer work in Single vs. Dual monitor computer work. A significant
Workstation main effect was found with significantly more overshoot in DualMon (p < .05) and
specifically in female participants (p < .00).
30
End Position Error (Degrees)
2.5
2
1.5
1
single
Dual
0.5
0
group
male female group
Pre
male female group
post
male female group
pre
male female
post
TO THE R
TO THE L
Time (Pre/Post) and Side (Right/Left)
Figure 7. Observed end position error during the head repositioning test in males and females
before and after 90min of computer work in Single vs. Dual monitor computer work. A
significant Workstation main effects was found overall with higher error in DualMon (p < .05).
Additionally, a significant Workstation main effect, with higher error in DualMon (p < .05) and a
significant Time x Workstation interaction effect (p < .05), with higher error in DualMon posttask, was found for female subjects.
31
4. Discussion
Our results show significant Workstations effects, in connection with the main aim of this
study. The DualMon workstation displayed significantly lower connectivity between RSCMRCES and RCES-LCES muscle pairs. It has been previously suggested that using two screens
requires more frequent head movements, and may be associated with greater bilateral variations
in muscle activity (Szeto et al., 2014), which could in turn require independent control of
bilateral CES muscles. Indeed, Szeto et al. (2014) found lower activation of the RCES but
significantly higher activation of the LCES during dual monitor computer work. Our results also
seem to point to this dissociative effect of dual computer work on CES with neighboring
muscles. Lower NMI has previously been interpreted as a beneficial muscle strategy during
fatigue in order to prevent spread of fatigue symptoms to neighbouring muscles (Fedorowich et
al., 2013). Svendsen et al. (2011) also observed lower NMI between forearm muscle pairs
during a dynamic task, suggesting lower NMI is a beneficial muscle strategy during active work.
Significantly lower muscle pairing in the DualMon condition may then reflect a protective
muscle response and thus an advantage of DualMon work, compared to laptop work.
The DualMon workstation showed significantly less RCES activity, an effect driven
primarily by female participants. Reported activation of the RCES during single vs. dual
monitor computer work has been mixed, as Szeto and colleagues (2014) found significantly
lower RCES 90th % amplitude probability distribution function (APDF) in the dual monitor
condition, while Nimbarte and colleagues (2013) observed that normalized CES activity was
unaffected by monitor layout and that there was an increase in RSCM activity in DualMon work.
Our results thus fall more in line with those of Szeto and colleagues, and could suggest a lower
load on the neck musculoskeletal structures in DualMon work (Fedorowich et al., 2015).
DualMon also demonstrated significantly more degrees of overshoot and end position error,
effects also primarily driven by female participants. Some researchers propose that greater
overshoot represents impaired proprioception (Heikkilä & Wenngren, 1998; Revel, AndreDeshays, & Minguet, 1991) as individuals displaying this pattern may be searching for additional
feedback from stretched antagonistic muscles (Armstrong et al., 2005). However, more recent
studies suggest that overshoot is a “normal behavior” during repositioning tests, occuring in 65-
32
80% of trials (Armstrong et al., 2005; Malmstrom et al., 2010). Armstrong et al. (2005)
observed consistent overshooting of the reference point irrespective of group (whiplash or
healthy) and movement direction, and reported mean absolute error scores comparable to those
for healthy individuals reported by others, with scores ranging from 2.3 to 4.0 ˚. Although
significantly more degrees of overshoot and end position error were seen here in the DualMon
condition, ranging from 3.5 to 5.1˚, they are similar to previously reported normal ranges. Thus,
overshoot results from our investigation, along with those from Armstrong et al., (2005) and
Malmstrom et al. (2010), suggest that overshoot may be a normal response to head-repositioning
tasks, and cast doubts on theories previously postulated by Heikkilä et al. (1998) and Revel et al.
(1991). In addition, it has also been reported that prolonged muscle contraction decreases
overshooting, and changes motion perception (Malmstrom et al., 2010), reinforcing that less
overshoot is not necessarily a sign of a healthier pattern. Overall, these results suggest that the
DualMon workstation may have aided in preserving the integrity of neck proprioceptive
structures. In our study, overshoot and end position error in the DualMon condition were more
prominent in female participants. Taken together, since lower RCES activity and a more typical
overshoot response to the head-repositioning task was observed in females, our results could
suggest that females respond better to DualMon workstations, although whether this truly
translates into a larger health protective effect in females should be verified using prospective
studies.
In addition to workstation effects, the main Time effects indicate time-dependent changes
in both workstations conditions. Visual strain was found to significantly increase over time,
independently from workstation condition. Visual strain is known to be significantly more
prevalent in computer workers than non-computer workers (Aarås, Horgen, Bjørset, Ro, &
Walsøe, 2001; Nakaishi & Yamada, 1999; Wolkoff et al., 2003; Woods, 2005) and to increase
with computer work time (Bergqvist & Knave, 1994; Blehm et al., 2005). RUT activity also
increased over time regardless of the workstation. Interestingly, Zetterberg and colleagues
(2013) found that visually demanding near work contributed to increased muscle activity in the
trapezius. Thus, we hypothesize that the significant increase in RUT activity observed with task
time in our study may be related to the increased visual strain experienced by participants over
33
the 90-minute computer work task, results which are seemingly in line with those of Zetterberg
and colleagues.
When separated by gender, time effects were only observed in male participants,
specifically in RUT and RAD activity. Greater muscle activity in the RUT and RAD suggests
that these muscles either worked harder or were more engaged over the course of the 90-minute
task, even though this is likely not associated with increasing visual strain in the same way as for
women, since eye strain increased with time in both gender sub-groups. We also observed
increased connectivity with time in the RUT-RMT and RAD-RCES pairs. Increased connectivity
between muscles has been previously suggested as a sign of fatigue (Fedorowich et al., 2015;
Madeleine, Samani, Binderup, & Stensdotter, 2011) and increased trapezius connectivity has
been previously observed in males, after shoulder eccentric exercise (Madeleine et al., 2011).
Moreover, increased connectivity between right side muscles could suggest a slow postural
adaptation to the external monitor placed on the right, which has a functional purpose but may
not necessarily equate to a healthy protective mechanism, given the association between
connectivity and symptoms in the literature. However, we also observed increased RMT
variability with time in males. This in turn could possibly be a compensatory preventative
strategy to overcome increased right side connectivity and-or some fatigue experienced within
the neck-shoulder muscles, given that the RUT and RAD activity increases over the course of the
task. Indeed, as it has been previously suggested that individuals who display less variability
may be at higher risk of developing musculoskeletal injuries (Madeleine, Mathiassen, et al.,
2008; Mathiassen et al., 2003), increased variability in males could possibly be a beneficial
muscle strategy in response to fatigue over prolonged computer work. Although the task used in
the present investigation was not intended to induce high levels of fatigue, fatigue could occur
with longer computer use durations and amplify the muscular patterns observed here.
Interestingly, these patterns were not observed in females. Indeed, several previous studies have
suggested the females display some muscular patterns that may be less injury protective. For
instance, Falla et al. (2008) found that females were less able to rearrange shoulder muscle
activity, and reported higher extents of perceived pain, when compared to their male counterparts
in response to muscle fatigue due to sustained shoulder abduction. Other studies have also
34
observed more activation of accessory muscles and less activation of primary muscle groups in
women (Anders et al., 2004). Our results together with results from previous investigations
further suggest differences in muscle activation strategies between men and women that could
place women at higher risk of computer work-related MSDs.
Results from this investigation may be limited to the type of computer workstation setup
(two screens) and task (relatively low stress and complexity) used in our study. Although the
task used in this investigation expanded on previous computer tasks of only typing (Fedorowich
et al., 2015), the task may not be representative of the wide range of office work that employees
perform. Additionally, the computer task was restricted to 90-minutes, limiting the
generalizability of the results to employees who work typical eight-hour workdays. However,
this experimental task was longer than that used by Szeto and Nimbarte who used a less than 30minute task, perhaps giving our results better generalizability to longer computer use durations.
The participants’ previous experience with dual monitor workstations could have potentially
influenced our results. Although most participants had limited to no previous experience with
dual monitor workstations, one participant was a habitual dual monitor user. However, no
notable differences in muscle activity outcomes, visual strain, or neck position sense were found
in this participant compared to other participants. Additionally, we allowed for a 5-minute
familiarization period prior to the start of the experiment to attempt to minimize possible
learning effects. The results from this investigation are also limited to healthy, young
populations with no pre-existing musculoskeletal complaints or injuries. This could limit the
generalizability of our results to patient populations. However, since we sought out to provide
normative data in response to these two types of workstations, we believe these results can be
useful in providing insight into the development of MSDs. Also, although values obtained from
the NMI analysis are quite small, and differ only in the thousandths place, they are comparable to
those obtained from Madeleine and colleagues in UT-MT and MT-LT muscle pairs during
dynamic contractions (Madeleine et al., 2011). However, functional interpretations of these
values are limited due to the analysis technique’s recent adaptation to the field. Finally, the neck
relocation task used to assess neck proprioception has previously been used in a number of
studies (Armstrong et al., 2005; Kristjansson, Dall'Alba, & Jull, 2003; Malmstrom et al., 2010;
35
Malmstrom et al., 2013; Pinsault et al., 2008), although, to date, there is no gold standard test to
assess neck proprioception.
In conclusion, the present study investigated the effects of two different workstations
(SingleMon and DualMon) on muscular, visual and proprioceptive outcomes during a
standardized 90-minute computer task. We initially hypothesized that the dual monitor
workstation would reveal beneficial muscular strategies, better neck position sense, and less
visual strain compared to the single monitor workstation. Indeed, DualMon seems to elicit some
beneficial neck/shoulder patterns as DualMon displayed lower neck muscular activity and more
typical responses to the head-repositioning test. Different effects in gender sub-groups in
muscular patterns and neck position sense were also observed, suggesting that men and women
respond differently to the two workstations, and to prolonged computer work. The novelty in
analysis techniques of this study contributes to the growing literature on single vs. dual monitor
workstations, and provides gender-based differences not previously reported in comparisons
between these types of workstations.
Acknowledgements
In addition to the participants of the study, the authors would like to thank Kim Emery, Larissa
Fedorowich, Hiram Cantu, Paul Rozakis, and William Franquet.
36
CONCLUSION
Results from this investigation further contribute to current knowledge on single vs. dual
computer workstations and work related sex differences, and provides some objective evidence
that can be considered when deciding on the use modalities of computer workstation designs.
Overall, the DualMon workstation elicited lower cervical muscle activity, more independent
control of neck muscles, and more typical neck repositioning responses when compared to the
SingleMon condition. Effects of DualMon work on muscle activity were more pronounced in
males, while proprioceptive responses were more pronounced in females, suggesting sex
differences in response to this computer workstation condition. The 90-minute task used in this
investigation also elicited a significant increase in visual strain and in upper trapezius muscle
activity over time, irrespective of workstation condition. These results suggest that dual monitor
workstation may provide some muscular and proprioceptive benefits, but that prolonged
computer work, regardless of workstation set-up, is still a significant risk factor in the
development of computer work related disorders. However, results from this investigation may
be limited to the type of computer workstation set up and the overall low cognitive demand of
the task. Although the task used here expanded on previous computer tasks of only typing
(Fedorowich et al., 2015), and was of longer duration that previous investigations in DualMon
versus SingleMon work (Nimbarte, Alabdulmohsen, Guffey, & Etherton, 2013; Szeto et al.,
2014) the generalizability of these results may still be limited. Additionally, participants had
varying levels of previous experience with DualMon workstations, possibly influencing our
outcome measures. The neck relocation test used to assess neck proprioception has been
previously used in a number of studies (Armstrong et al., 2005; Kristjansson et al., 2003;
Malmstrom et al., 2010; Malmstrom et al., 2013; Pinsault et al., 2008), however there is currently
no gold standard test. In addition, the nature of this test does not allow for the experimenter to
control the position of the individual’s neutral head position, resulting in unique neutral positions
for each subject with respect to the origin in the kinematic system. Future research should aim to
introduce dual monitor workstations to populations with chronic neck/shoulder pain to see their
possible effectiveness in reducing symptoms. Additionally, since this investigation was cross-
37
sectional in nature, future studies should aim to measure long-term effects of dual monitor
workstations, both in healthy and symptomatic populations.
38
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46
Consent form
1-
Title of project
Muscular, postural, and vascular characteristics of computer work with one versus multiple
computer monitors
2-
Researcher in charge of project
Julie Côté, Ph.D. Associate Professor, Department of Kinesiology and
Physical Education, McGill University, (514) 398-4184 ext. 0539, (450) 688-9550, ext.
4813.
Amanda Farias, B.Sc. Master Student in Kinesiology, McGill University, (450) 688-9550, ext
4827
Kim Emery, M.Sc. Research Assistant, Jewish Rehabilitation Hospital/McGill University, (450)
688-9550, ext 4827
3-
Introduction
Before agreeing to participate in this project, please take the time to read and carefully
consider the following information.
This consent form explains the aim of this study, the procedures, advantages, risks and
inconvenience as well as the persons to contact, if necessary.
This consent form may contain words that you do not understand. We invite you to ask any
question that you deem useful to the researcher and the others members of the staff assigned to
the research project and ask them to explain any word or information which is not clear to you.
4-
Project description and objectives
The objective of this research is to compare the effects of single versus dual monitor computer
work on muscular, postural and vascular outcomes, as well as eye-strain outcomes. Another
objective is to assess the effects of computer work time on these same outcomes. Fourteen
healthy females and fourteen healthy male adults will be recruited to complete this study.
47
Participants will perform 2 sessions of computer work in 2 different workstations (using one
computer monitor and using two computer monitors) in which they will be asked to work at a
computer for 90 minutes (reading, typing, and search and find tasks). Equipment will be placed
on participants in order to record muscle activity, blood flow and tridimensional posture. The
long-term objectives of this research are to better understand and quantify the impact of
computer workstation on health outcomes.
5-
Nature and duration of participation
The research project in which you are invited to participate aims at understanding the
impact that the computer workstation has on muscles, posture, blood flow, and eye strain. The
experimental procedure will be performed at the research center of the Jewish Rehabilitation
Hospital. You are asked to participate in 2 experimental sessions, which will last approximately
three hours each, with at least 48 hours in between. During each session, we will ask you to wear
sport shoes and a tight fitting tank top.
If you choose to participate in this study, there will be two phases in each session: a preparation
phase, and an experimental phase. The preparation phase will last approximately 1 hour and will
remain the same for the 2 sessions. Surface electrodes will be fixed on the skin over muscles of
your trunk and arms in order to measure muscle activity and blood flow. Reflective markers will
be placed over your trunk and arms in order to measure their movements. None of these
procedures are invasive. Baseline (rest) measures will be recorded. You will be asked to
complete several efforts using your trunk and arm muscles. You will also be asked to fill out a
brief questionnaire, which aims to measure the amount of eye fatigue that you experience.
Finally, your visual acuity will be assessed.
After the preparation phase, you will be asked to perform a computer task in one of the chosen
workstations (single or dual monitor) for a total of 90 minutes (Figure 1). The computer task will
consist of reading, typing, and searching. You will be given a practice period before the test
period begins. At various points during the task the research equipment will collect data. Each
10min, you will be asked to stop working for about 1min so that other data can be collected. At
various points during the experiment, the researcher will ask you to rate your eye discomfort
during the task. You are free to leave the experiment at any point if you do not wish to continue,
or if you are not comfortable with the procedure. You will be asked to come back a second time
in order to test both workstations.
48
Figure 1: experimental setup. Please note that there will not be electrodes placed on the lower back in the
present experiment. Participants will normally wear a tight fitting tank top but can also elect to perform
the protocol bare chested if they prefer.
6-
Advantages associated with my participation
As a participant you will receive no direct benefit from your involvement in this study.
However, you will contribute to the fundamental science of human physiology and biomechanics
and to applied knowledge in ergonomics and occupational health.
7-
Risks associated with my participation
None of the techniques used are invasive. Your participation in this project does not put
you at any medical risk.
8-
Personal inconvenience
The duration of each session (approximately 3 hours) and the fact that you need to come
two times may represent an inconvenience for you. The possibility that a few small areas (11,
3x3 cm each) of the skin over your neck, back and arms may have to be shaved before
positioning the electrodes might also be an inconvenience to you. The material used respects the
usual hygiene norms. However, although it is hypo-allergenic, the adhesive tape used to fix the
electrodes on your skin may occasionally produce some slight skin irritation. Should this happen,
a hypo-allergic lotion will be applied on your skin to relieve skin irritation. You may experience
some slight fatigue towards the end of the session, which may cause some neck and-or arm
muscle tenderness or stiffness. If this occurs, symptoms should dissipate within 48 hours
following the completion of the protocol. A clinician will be present at all times during the
protocol in case of allergic reaction, non-anticipated injury or accident.
49
9-
Access to my medical file
No access to your medical file is required for this study.
10 -
Confidentiality
All the personal information collected for this study will be codified to insure its
confidentiality. Only the people involved in the project will have access to this information.
However, for means of control of the research project, your research records could be consulted
by a person mandated by the REB of the CRIR establishments or by the ethics unit of the
Ministry of health and social services, which adheres to a strict confidentiality policy.
Information will be kept under locking key at the research center of the Jewish Rehabilitation
Hospital by the person responsible for the study for a period of five years following the end of
the study, after which it will be destroyed. If the results of this research project are presented or
published, nothing will allow your identification.
12 -
Withdrawal of subject from study
Participation in the research project described above is completely voluntary. You have the
right to withdraw from the study at any moment. If ever you withdraw from the study, all
documents concerning yourself will be destroyed at your request.
13 -
Responsibility
By accepting to participate in this study, you do not surrender your rights and do not free
the researchers, sponsor or the institutions involved from their legal and professional obligations.
14 -
Monetary compensation
No monetary compensation will be given to you for participation in this protocol.
Transport costs encumbered by our participation in this research can be reimbursed upon request
and upon receipt of appropriate documentation.
15 -
Contact persons
If you need to ask questions about the project, signal an adverse effect and/or an incident,
you can contact at any time Amanda Farias at [email protected] or at 514-826-0270.
50
For further questions related to this study, you may also contact M. Michael Greenberg, local
commissioner for complaints at the JRH, at (450) 688-9550, extension 232.
Also, if you have any questions concerning your rights regarding your participation to
this research project, you can contact Ms. Anik Nolet, Research ethics co-ordinator of CRIR at
(514) 527-4527 ext. 2649 or by email at [email protected].
51
CONSENT
I declare to have read and understood the project, the nature and the extent of the project,
as well as the risks and inconveniences I am exposed to as described in the present
document. I had the opportunity to ask all my questions concerning the different aspects of
the study and to receive explanations to my satisfaction.
I, undersigned, voluntarily accept to participate in this study. I can withdraw at any time
without any prejudice. I certify that I have received enough time to take my decision.
A signed copy of this information and consent form will be given to me.
NAME OF PARTICIPANT (print):
________________________________
SIGNATURE OF PARTICIPANT:
________________________________
SIGNED IN _____________________, on _________________, 20_____.
52
COMMITMENT OF RESEARCHER
I, undersigned, ________________________________, certify
(a) having explained to the signatory the terms of the present form ;
(b) having answered all questions he/she asked concerning the study ;
(c) having clearly told him/her that he/she is at any moment free to withdraw from the
research project described above; and
(d) that I will give him/her a signed and dated copy of the present document.
___________________________________
Signature of person in charge of the project
or representative
SIGNED IN __________________, on _________________________ 20__.
53
Formulaire de consentement
1-
Titre du projet
Caractéristiques musculaires, posturales et vasculaires du travail à l’ordinateur avec un versus
plusieurs écrans
2-
Responsable(s) du projet
Julie Côté, Ph.D. professeure agrégée, département de kinésiologie et d’éducation physique,
université McGill, (514) 398-4184 poste 0539, (450) 688-9550, poste 4813.
Amanda Farias, B.Sc. Étudiante à la maîtrise en en kinésiologie, université McGill, (450) 6889550, ext 4827
Kim Emery, M.Sc. Assistante de recherche, Hôpital Juif de Réadaptation/Université McGill,
(450) 688-9550, poste 4827
3-
Préambule
Avant d'accepter de participer à ce projet de recherche, veuillez prendre le temps de
comprendre et de considérer attentivement les renseignements qui suivent.
Ce formulaire de consentement vous explique le but de cette étude, les procédures, les
avantages, les risques et inconvénients, de même que les personnes avec qui communiquer au
besoin.
Le présent formulaire de consentement peut contenir des mots que vous ne comprenez pas.
Nous vous invitons à poser toutes les questions que vous jugerez utiles au chercheur et aux autres
membres du personnel affecté au projet de recherche et à leur demander de vous expliquer tout
mot ou renseignement qui n'est pas clair.
4-
Description du projet et de ses objectifs
L’objectif de cette recherche est de comparer les effets du travail à l’ordinateur avec un versus
deux écrans sur les paramètres musculaires, posturaux et vasculaires, ainsi que sur les mesures de
fatigue visuelle. Un autre objectif est d’évaluer les effets du temps de travail à l’ordinateur sur
ces mêmes paramètres. Quatorze femmes et quatorze hommes en santé seront recrutés pour
participer à cette étude. Les participants effectueront deux séances de travail à l’ordinateur à
deux postes de travail différents (avec un écran d’ordinateur, avec deux écrans d’ordinateur) lors
54
desquelles on leur demandera de travailler à l’ordinateur pendant 90 minutes (tâches de lecture,
d’écriture et de recherche). L’équipement sera fixé sur les participants afin de mesurer l’activité
des muscles, le flux sanguin et la posture tridimensionnelle. Les objectifs à long terme de cette
recherche sont de mieux comprendre et quantifier l’impact du travail à l’ordinateur sur les
indicateurs de santé.
5-
Nature et durée de la participation
Le projet de recherche auquel vous êtes invité(e) à participer cherche à comprendre
l’impact que le poste de travail à l’ordinateur a sur les muscles, la posture, le flux sanguin et la
fatigue visuelle. Le protocole de recherche sera effectué au centre de recherche de l’Hôpital juif
de réadaptation. On vous demande de participer à une séance expérimentale d’une durée
approximative de 2 heures. Durant la séance, on vous demandera de porter des souliers de sport
et une camisole ajustée à la peau.
Si vous acceptez de participer à cette étude, il y aura deux phases durant chaque séance : une
phase de préparation et une phase expérimentale. La phase de préparation durera environ une
heure et sera la même pour les deux séances. Des électrodes de surface seront fixées sur la peau
de colonne et de vos bras afin de mesurer l’activité des muscles et le flux sanguin. Des
marqueurs réfléchissants seront fixés sur la peau de vos bras et votre colonne afin de mesurer
leurs déplacements. Aucune de ces procédures n’est invasive. Des mesures de base (repos) seront
effectuées. On vous demandera aussi d’effectuer quelques efforts maximaux avec les muscles de
vos bras et de votre colonne. Vous allez aussi remplir un questionnaire comportant des questions
sur la fatigue visuelle que vous ressentez. Finalement, votre acuité visuelle sera mesurée.
Après la phase de préparation, vous effectuerez une tâche à l’ordinateur à un des postes
sélectionnées (un ou deux écrans) pendant un total de 90 minutes (Figure 1). La tâche consistera
en de la lecture, de l’écriture et de la recherche. Vous aurez une période de pratique avant le
début de la période de test. À des moments différents durant la tâche, l’équipement de recherche
enregistrera des données. Chaque 10min, on vous demandera d’interrompre la tâche pour environ
1min pour nous permettre d’enregistrer d’autres données. À d’autres moments durant le
protocole, le chercheur vous demandera d’évaluer votre inconfort visuel durant la tâche. Vous
serez libre d’abandonner le protocole à tout moment si vous ne voulez pas continuer ou si vous
êtes inconfortable à propos de la procédure. On vous demandera de venir une deuxième fois afin
d’évaluer les deux postes de travail.
55
Figure 1 : montage expérimental. À noter que dans ce protocole, il n’y aura pas d’électrodes placées sur le
bas du dos. Les participants porteront normalement une camisole ajustée à la peau mais pourront effectuer
le protocole torse nu s’ils préfèrent.
6-
Avantages pouvant découler de votre participation
En tant que participant, vous ne retirerez personnellement pas d’avantages à participer à
cette étude. Toutefois, vous aurez contribué à l’avancement de la science fondamentale de la
physiologie humaine et de la biomécanique et aux connaissances appliquées de l’ergonomie et la
santé au travail.
7-
Risques pouvant découler de votre participation
Aucune des procédures décrites n’est invasive. Votre participation à cette recherche ne
vous fait courir aucun risque médical.
8-
Inconvénients personnels
La durée de la séance expérimentale (environ deux heures chacune) peut représenter un
inconvénient pour certaines personnes. La possibilité que quelques régions (11, 3x3 cm chaque)
de la peau de votre cou, de votre dos et de vos bras doivent être rasées avant d’y apposer des
électrodes peut également représenter un inconvénient pour vous. Le matériel utilisé respecte les
règles d’hygiène usuelles. Toutefois, bien qu’il soit hypo-allergène, le ruban adhésif utilisé pour
maintenir les électrodes sur la peau peut occasionnellement provoquer de légères irritations de la
peau. Le cas échéant, une lotion hypo-allergène sera appliquée pour soulager l’irritation cutanée.
De plus, il est possible que vous ressentiez un peu de fatigue vers la fin de la séance
expérimentale, ce qui pourrait causer de la sensibilité ou de la raideur des muscles du cou et-ou
des bras. S’ils se manifestent, les symptômes devraient disparaître dans les 48 heures suivant la
56
fin du protocole expérimental. Un clinicien sera présent en tout temps durant le protocole en cas
de réaction allergique, blessure ou accident non anticipés.
9Accès à mon dossier médical
L’accès à votre dossier médical n’est pas requis pour cette étude.
10 -
Confidentialité
Tous les renseignements personnels recueillis à votre sujet au cours de l’étude seront
codifiés afin d’assurer leur confidentialité. Seuls les membres de l’équipe de recherche y auront
accès. Cependant, à des fins de contrôle du projet de recherche, votre dossier de recherche
pourrait être consulté par une personne mandatée par le CÉR des établissements du CRIR ou de
l’Unité de l’éthique du ministère de la Santé et des Services sociaux, qui adhère à une politique
de stricte confidentialité. Les données seront conservées sous clé au centre de recherche de
l’Hôpital juif de réadaptation par le responsable de l’étude pour une période de 5 ans suivant la
fin du projet, après quoi, elles seront détruites. En cas de présentation de résultats de cette
recherche ou de publication, rien ne pourra permettre de vous identifier.
12 -
Retrait de la participation du sujet
Votre participation au projet de recherche décrit ci-dessus est tout à fait libre et
volontaire. Il est entendu que vous pourrez, à tout moment, mettre un terme à votre participation.
En cas de retrait de votre part, les documents électroniques et écrits vous concernant seront
détruits à votre demande.
13 -
Clause de responsabilité
En acceptant de participer à cette étude, vous ne renoncez à aucun de vos droits ni ne
libérez les chercheurs, le commanditaire ou les institutions impliquées de leurs obligations
légales et professionnelles.
14 -
Indemnité compensatoire
Aucune compensation financière ne vous sera offerte pour votre participation à cette étude.
Des frais de déplacement encourus par la participation à cette recherche pourront vous être
remboursés à votre demande et sur présentation de pièces justificatives.
15 -
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Personnes ressources
Si vous désirez poser des questions sur le projet ou signaler des effets secondaires, vous
pouvez rejoindre en tout temps Xin Wei Yan, à [email protected], ou au (450) 6889550 poste 4827. Vous pouvez également contacter Monsieur Michael Greenberg, commissaire
local aux plaintes de l’HJR, au (450) 688-9550 poste 232.
De plus, si vous avez des questions sur vos droits et recours ou sur votre participation à
ce projet de recherche, vous pouvez communiquer avec Me Anik Nolet, coordonnatrice à
l’éthique de la recherche des établissements du CRIR au (514) 527-4527 poste 2649 ou par
courriel à l’adresse suivante: [email protected]
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CONSENTEMENT
Je déclare avoir lu et compris le présent projet, la nature et l’ampleur de ma participation,
ainsi que les risques auxquels je m’expose tels que présentés dans le présent formulaire.
J’ai eu l’occasion de poser toutes les questions concernant les différents aspects de l’étude
et de recevoir des réponses à ma satisfaction.
Je, soussigné(e), accepte volontairement de participer à cette étude. Je peux me retirer en
tout temps sans préjudice d’aucune sorte. Je certifie qu’on m’a laissé le temps voulu pour
prendre ma décision.
Une copie signée de ce formulaire d’information et de consentement doit m’être remise.
NOM DU SUJET
________________________________________
SIGNATURE
________________________________________
Signé à _________________________,
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le ___________, 20_____.
ENGAGEMENT DU CHERCHEUR
Je, soussigné (e), ________________________________ , certifie
(a) avoir expliqué au signataire les termes du présent formulaire;
(b) avoir répondu aux questions qu'il m'a posées à cet égard;
(c) lui avoir clairement indiqué qu'il reste, à tout moment, libre de mettre un terme à sa
participation au projet de recherche décrit ci-dessus;
et (d) que je lui remettrai une copie signée et datée du présent formulaire.
______________________________
Signature du responsable du projet
ou de son représentant
Signé à __________________, le ______________ 20__.
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