Effort–reward imbalance and one-year change in neck–shoulder and upper-
extremity pain among call center computer operators
by Niklas Krause, MD, PhD,1 Barbara Burgel, RN, PhD,2 David Rempel, MD 1
Krause N, Burgel B, Rempel D. Effort–reward imbalance and one-year change in neck–shoulder and upper-extremity
pain among call center computer operators. Scand J Work Environ Health. 2010;36(1):42–53.
Objective The literature on psychosocial job factors and musculoskeletal pain is inconclusive in part due to insuf-
ficient control for confounding by biomechanical factors. The aim of this study was to investigate prospectively
the independent effects of effort–reward imbalance (ERI) at work on regional musculoskeletal pain of the neck
and upper extremities of call center operators after controlling for (i) duration of computer use both at work and
at home, (ii) ergonomic workstation design, (iii) physical activities during leisure time, and (iv) other individual
Methods This was a one-year prospective study among 165 call center operators who participated in a random-
ized ergonomic intervention trial that has been described previously. Over an approximate four-week period,
we measured ERI and 28 potential confounders via a questionnaire at baseline. Regional upper-body pain and
computer use was measured by weekly surveys for up to 12 months following the implementation of ergonomic
interventions. Regional pain change scores were calculated as the difference between average weekly pain scores
pre- and post intervention.
Results A significant relationship was found between high average ERI ratios and one-year increases in right
upper-extremity pain after adjustment for pre-intervention regional mean pain score, current and past physical
workload, ergonomic workstation design, and anthropometric, sociodemographic, and behavioral risk factors. No
significant associations were found with change in neck–shoulder or left upper-extremity pain.
Conclusions This study suggests that ERI predicts regional upper-extremity pain in computer operators working
≥20 hours per week. Control for physical workload and ergonomic workstation design was essential for identify-
ing ERI as a risk factor.
Key terms ERI; job stress; musculoskeletal disorder; ���;occupa
display terminal; video display unit.
���; occupaoccupational epidemiology; prospective study; video
1 �ivision of Occupational and Environmental �edicine, �epartment of �edicine, University of California, �an Francisco, U�A
2 �epartment of Community Health �ystems, �chool of Nursing, University of California, �an Francisco, U�A
Correspondence to: �r N Krause, University of California at �an Francisco UC Berkeley Richmond Field �tation, 1301 �outh 46th �treet,
Building 163, Richmond, CA 94804, U�A. [E-mail: email@example.com]
It is a widely shared concept in occupational epide-
miology that musculoskeletal disorders have a multi-
factorial etiology, involving exposure to both physical
and psychosocial working conditions (1–4). Empirical
evidence for a causal role of psychosocial working
conditions, however, is inconclusive. Until a few years
ago, this research area was characterized by an over-
reliance on cross-sectional studies (5, 6). In recent
years, a considerable number of new longitudinal stud-
ies have been conducted, but the findings have been
inconsistent. A review covering 18 longitudinal stud-
ies on psychosocial workplace factors and low-back
pain found “insufficient evidence for an association
between stress at work and low-back pain” (5, p 9).
A review that analyzed 19 studies on psychosocial
workplace factors and neck–shoulder symptoms con-
cluded that “this relationship is neither very strong nor
very specific” (6, p 290). The two reviews criticized
that many studies have not sufficiently controlled for
exposure to high physical workload and ergonomic
problems (7, 8). Finally, it is notable, that many studies
defined psychosocial working conditions based on the
demand–control (job strain) model (9) or its expansion,
the demand–control–support model (10), and that there
is a lack of research on alternative theoretical models of
psychosocial workplace stressors.
Effort–reward imbalance model
In recent years, the model of effort–reward imbal-
ance (ERI) at work has emerged as a new theoretical (ERI) at work has emerged as a new theoreticalat work has emerged as a new theoretical
approach for conceptualizing health-hazardous psycho-
social working conditions. The model posits that a “high
cost–low gain” situation at work, in which individuals
spend high efforts while receiving low rewards (in terms
of monetary gratification, career opportunities, esteem,
respect, and job security), elicits severe psychologi-
cal distress that consequently affects both mental and
physical health (11–14). It is further assumed in the
model that ERI has, in particular, adverse health con-
sequences when it co-occurs with “over-commitment
(intrinsic effort)”. Over-commitment is conceptualized
as a personal disposition that motivates people to spend
high efforts even in a situation where the chance for a
reward is low.
The ERI model has been tested most intensively
in cardiovascular research, where it has been found to
be associated with incident cardiovascular events in
longitudinal studies (15). For other health outcomes,
the empirical evidence has been less comprehensive
(for reviews see 13 and 14) although there is increasing
evidence that ERI might predict the onset of common
mental disorders (16, 17).
The vast majority of research studies on ERI and
health endpoints have been conducted in Europe, and
there are very few studies that have tested this model in
the United �tates. Burgel et al (18) found that ERI was
associated cross-sectionally with severe shoulder pain in
hotel room cleaners. Gillen et al (19) found that it was
associated with a risk of neck and upper-extremity injury
claims in a case-control study among hospital workers in
�an Francisco, U�A. Rugulies & Krause (20) reported
that ERI predicted compensated low-back and neck
injuries in a 7.5-year prospective study of urban transit
operators in �an Francisco. However, to our knowledge,
there are no published studies in the U� that have inves-
tigated the health effects of ERI on upper-body, regional
pain among computer operators in the rapidly growing
call center industry.
Call center work
Computer-based customer service work, or call center
work, is one of the most rapidly growing occupations
in the world (21). The work involves the simultaneous
use of a telephone and computer for activities such as
airline reservations, banking, sales, insurance, schedul-
ing, billing, and health-related services. �usculoskeletal
disorders of the upper extremities and neck are the most
common occupational health problem associated with this
type of work and account for the majority of work-related
lost time (21, 22). �ustained pain in the upper-extremity
and neck regions and specific musculoskeletal disorders
(such as wrist tendonitis, epicondylitis and trapezius
muscle strain) are elevated among computer users. The
most consistently observed risk factors are increasing
hours of mouse or keyboard use and sustained awkward
postures, such as increasing wrist extension and key-
board-above-elbow height (23–28). Other important risk
factors include being female and work organizational
factors (eg, high work load, low job control) (29, 30).
The association of carpal tunnel syndrome with keyboard
use is weak, but there is some evidence of increased risk
with increasing hours of computer mouse use (31, 32).
A randomized controlled study of ergonomic workplace
interventions showed a protective effect of forearm sup-
port boards for neck–shoulder disorders and a reduction
of neck–shoulder and right upper-extremity pain in call
center employees after control for psychosocial job fac-
tors, individual worker characteristics, medical history,
and other confounding factors (33).
The aim of this study was to investigate prospectively
the independent effects of ERI at work on regional
musculoskeletal pain of the neck and upper extremities
of call center operators after controlling for (i) physical
workload, (ii) leisure-time computer use, (iii) ergo-
nomic workstation design, and (iv) individual worker
Study design and population
This was a one-year prospective study of ERI and
upper-body musculoskeletal pain among 165 call cen-
ter operators who participated in a randomized ergo-
nomic intervention trial with four treatment channels
described previously (33). Employees at two customer
service center sites of a large health maintenance
organization (H�O) in California were eligible for par-
ticipation if they performed computer-based customer
service work for ≥20 hours per week and did not
have an active workers’ compensation claim involving
the neck, shoulders, or upper extremities. At on-site
recruitment meetings, between June 2001 and �ay
2002, the study was explained, and interested employ-
ees who met the initial eligibility criteria signed a con-
sent form (N=269). These potential participants filled
out a self-administered baseline questionnaire and then,
on a weekly basis, completed a one-page question-
naire which assessed pain severity. Employees who
completed at least four weekly surveys were eligible
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Received for publication: 10 July 2009