Wassell JT, Gardner LI, Landsittel DP, Johnston JJ, Johnston JM. A Prospective Study of Back Belts for Prevention of Back Pain and Injury. JAMA. 2000;284(21):2727-2732. doi:10.1001/jama.284.21.2727
Author Affiliations: Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Division of Safety Research, Morgantown, WVa. Dr Gardner is now with National Center for HIV, STD and TB Prevention. Dr Landsittel is now with the National Institute for Occupational Safety and Health, Health Effects Laboratory Division. Dr Janet M. Johnston is now with the University of Pittsburgh, Graduate School of Public Health, Pittsburgh, Pa.
Context Despite scientific uncertainties about effectiveness, wearing back belts
in the hopes of preventing costly and disabling low back injury in employees
is becoming common in the workplace.
Objective To evaluate the effectiveness of using back belts in reducing back injury
claims and low back pain.
Design and Setting Prospective cohort study. From April 1996 through April 1998, we identified
material-handling employees in 160 new retail merchandise stores (89 required
back belt use; 71 had voluntary back belt use) in 30 states (from New Hampshire
to Michigan in the north and from Florida to Texas in the south); data collection
ended December 1998, median follow-up was 6½ months.
Participants A referred sample of 13,873 material handling employees provided 9377
baseline interviews and 6311 (67%) follow-up interviews; 206 (1.4%) refused
Main Outcome Measures Incidence rate of material-handling back injury workers' compensation
claims and 6-month incidence rate of self-reported low back pain.
Results Neither frequent back belt use nor a belt-requirement store policy was
significantly associated with back injury claim rates or self-reported back
pain. Rate ratios comparing back injury claims of those who reported wearing
back belts usually every day and once or twice a week vs those who reported
wearing belts never or once or twice a month were 1.22 (95% confidence interval
[CI], 0.87-1.70) and 0.95 (95% CI, 0.56-1.59), respectively. The respective
odds ratios for low back pain incidence were 0.97 (95% CI, 0.83-1.13) and
0.92 (95% CI, 0.73-1.16).
Conclusions In the largest prospective cohort study of back belt use, adjusted for
multiple individual risk factors, neither frequent back belt use nor a store
policy that required belt use was associated with reduced incidence of back
injury claims or low back pain.
Back injuries have been the leading cause of disability in the United
States for people younger than 45 years and have been the most expensive health
care problem for the 30- to 50-year-old age group.1
Low back pain accounted for 23% ($8.8 billion) of total workers' compensation
payments in 1995.2 The Annual Survey of Occupational
Injuries and Illnesses conducted by the Bureau of Labor Statistics indicates
that in 1998 there were 279,507 back injuries due to overexertion that resulted
in lost work days (89% in material-handling).3
In response to the increasing human and economic costs of back injury, employers
have attempted preventive measures; specifically, the widespread use of industrial
back belts, approximately 4 million of which were purchased in 1995.4 This study was designed to address 2 objectives: (1)
to examine the effect of store policy by comparing a belt-use requirement
policy with a voluntary belt-use policy and (2) to compare employees who reported
wearing back belts usually every day with those reported wearing the belt
less frequently, based on interview responses.
Between April 1996 and April 1998, 50 new stores and 110 newly expanded
stores (combination supermarket and merchandise) of a single corporation were
enrolled on the date they first opened for regular business. A prospective
cohort study was conducted following sequential assignment (according to store
opening date) of groups of stores to either the traditional belt-requirement
policy or voluntary belt use. Employees were required to wear back belts during
material-handling activities in the belt-requirement stores, while belts were
made available only by request in the voluntary belt-use stores.
Of the 160 stores in the study, 89 required back-belt use and 71 had
voluntary belt use. The original goals of introducing stores with voluntary
belt use were to create an environment in which employees were free not to
wear back belts without violating store policy and to compare the back injury
rate with stores that required belt use. The main focus of this study is on
interview data: determining employee characteristics and belt wearing habits
from a baseline interview for comparison of injury rates and a follow-up interview
to determine the incidence of self-reported low back pain.
Study stores were distributed across 30 states from New Hampshire to
Michigan in the north and from Florida to Texas in the south; most states
included both belt-requirement and voluntary belt-use stores. We obtained
payroll records of hours worked and workers' compensation injury reports for
all stores for calculation of injury incidence rates. The National Institute
for Occupational Safety and Health (NIOSH) Human Subjects Review Board formally
approved the study's design and data collection instruments in August 1995,
following a public peer review meeting in April 1995.
A survey contractor conducted telephone interviews using trained interviewers.
Participants completed an informed consent form either in a prestudy employee
meeting or at the beginning of the telephone interview. Telephone calls were
placed to employees while working at the store during regular working hours.
For each store, interviews were attempted for a period of at least 30 calendar
days (excluding weekends). Follow-up interviews were attempted for all employees
who had a baseline interview. Interviews were not conducted from mid-December
to mid-January due to the holiday shopping season.
Both the baseline and follow-up interviews consisted of questions covering
work history, lifestyle habits, medical history, job activities, psychosocial
factors, belt wearing habits, and demographic information. Participants were
asked 4 job satisfaction questions from the Quality of Employment Survey developed
by the US Department of Labor and NIOSH.5 The
sum of the responses for these 4 items were used to create a dichotomous measure
of job satisfaction using the median cut point.
The job title receiver/unloader identified
workers with the greatest exposure to physical work unloading freight trucks; stocker was used to designate employees with responsibility
for moving stock to the merchandise floor. Department managers were employees whose physical work mostly involved arranging stock
on shelves and other less strenuous activities, and the group designated as others were employees with various other jobs involving
material handling. In a separate study6 receiver/unloaders
had the highest exposure to manual material handling (based on lifting heavier
loads more frequently), followed by department managers, then stockers. Job
title was determined from an employee's first baseline interview response
and consistency in reporting job title was evaluated from the follow-up interview:
85% of department managers, 75% of stockers, 71% of receiver/unloaders, and
31% of the others were working in the same job title that they reported during
the baseline interview.
Self-reported belt wearing was determined from the response to the question:
"During the past month, how many days per week did you wear the back belt?"
Response categories were: "never," "once or twice a month," "once or twice
a week," or "usually every day." The "never" and "once or twice a month" categories
were combined and are referred to herein as never. Consistency was evaluated
from the follow-up interview with 75% reporting usually every day, 81% reporting
never, and 31% reporting once or twice per week in the same baseline category.
The back belt provided by the corporation is designed to fit around
the waist without shoulder straps. The belt is constructed of stretchable
nylon material with Velcro ends and mesh in back. Tightness is adjusted by
choosing the location to attach the Velcro and tightening side panels when
lifting. This same back belt was used in human subjects laboratory studies
of biomechanics (Rebecca J. Giorcell, PhD, et al, unpublished data, 1998)
and physiology effects (Thomas G. Bobick, PhD, et al, unpublished data, 1998).
All employees, when first hired and regardless of the store policy, received
a short introductory information and training session on proper lifting and
belt use via videotape or interactive computer-based learning.
Self-reported low back pain (hereafter back pain) was defined as a positive
response to a question asking if respondents experienced any low back pain
in the 6 months preceding the follow-up interview, with a frequency of 4 or
more episodes (≥median). A history of previous back injury was determined
by a positive response to questions about back pain (with the addition of
a reported severity ≥7 on a 10-point scale) at the baseline interview;
had previous back surgery; had "ever been told by a doctor" that he/she had
arthritis of back joints, degenerative joint disease of the back, lupus erythematosus,
ankylosing spondylitis, or spondylolisthesis; or had "seen a doctor, nurse,
physical therapist, or chiropractor" for a strain or sprain of the lower back
or ruptured disk in the back.
The data consisted of the dates of occurrence and characteristics of
work-related material-handling back injuries requiring medical care recorded
in the company's own workers' compensation reporting system. The data consisted
of all claims received by the corporation, regardless of whether the claim
was accepted or rejected for compensation. Although compensation rules vary
among states, corporation procedures and policies regarding which injuries
are included in their corporate database do not vary among states. Material-handling
compensation claims for back injuries consisted of those with an external
cause code containing "strain" or "sprain" followed by "lifting," "pushing,"
"pulling," "reaching," "holding," or "carrying." Back injuries unrelated to
material handling (such as "fall," "caught by," "caught between," "struck
by," "slip," or "trip without fall") were excluded.
The regression models used to investigate the effects of belt wearing
and store policy were selected to control for type of store (new stores or
newly expanded stores that are a combination of supermarket and merchandise),
demographic risk factors (age, race, and sex), work exposure (job title and
lifting frequency), variables found important in previous studies (history
of previous back injury and job satisfaction), and a standard health-risk
factor (smoking). These 11 covariates were investigated using Poisson regression
to model the incidence rate of back injury claims, taking account of the variable
work-hours of follow-up for each employee. Logistic regression was used to
model the incidence of back pain as a binary outcome in which employees had
similar length of follow-up. Potential effect modification was investigated
using interaction terms and separate analysis of subgroups of data. Subgroup
analyses were conducted for those who were concordant for belt wearing at
both the baseline and follow-up interviews and for employees with the most
strenuous job tasks. Regression analyses and confidence intervals (CIs) for
odds ratios (ORs) and rate ratios (RRs) were calculated using SAS statistical
software.7 Other CIs were calculated using
There were a total of 144,469 employees who worked in the 160 stores
during the study period. Of these, 13,873 (10%) were identified by store management
as involved in material handling tasks prior to the interview process (Figure 1). For the 6311 employees who completed
both a baseline and a follow-up interview, the median (and mode) of the length
of time between baseline and follow-up interview was 6½ months. Payroll
and workers' compensation data collection ended December 1998.
Table 1 shows employee characteristics
from the baseline interview by store-belt policy and belt wearing. There was
a lack of compliance with the store belt-wearing policy. In the stores requiring
belt use, 58% of employees reported wearing belts usually every day; 14%,
once or twice a week; and 28%, never. In the stores with voluntary belt-use,
33% of employees reported wearing belts usually every day; 11%, once or twice
a week; and 56%, never. There was a slight difference in the proportions who
completed a follow-up interview, worked in new stores, or had a history of
previous back injury by frequency of belt wearing. Employees who reported
belt wearing usually every day were more likely to be receivers/unloaders
or stockers and were less likely to be department managers or others, and
were also more likely to report lifting more than 9 kg (20 lb) at work usually
Among the 9377 who completed a baseline interview and were matched to
payroll data, there were 195 back injury claims (12.9 million work-hours)
for a crude incidence rate of 3.03 per 100 full-time equivalent (FTE) (95%
CI, 2.62-3.48). Among the 6311 who completed a baseline and follow-up interview,
there were 1088 cases of back pain (17%; 95% CI, 16%-18%). There were no statistically
significant protective effects comparing employees who wore belts usually
every day with employees who never wore belts for either back injury claims
(RR, 1.22; 95% CI, 0.87-1.70) or low back pain (OR, 0.97; 95% CI, 0.83-1.13).
There were no statistically significant protective effects comparing employees
who wore belts once or twice a week with employees who never wore belts for
either back injury claims (RR, 0.95; 95% CI, 0.56-1.59) or back pain (OR,
0.92; 95% CI, 0.73-1.16). Table 2
presents percentages reporting back-pain and back injury claim rates, stratified
by risk factors. Table 2 also
presents multivariate regression estimates with each variable adjusted for
all other variables listed.
Among the other risk factors in the models, a history of previous back
injury was the strongest risk factor for both outcomes. Frequent lifting of
heavier than 9 kg (20 lb) at work was associated with significantly increased
odds of back pain but not for back injury claims. Women had significantly
more back pain than men, but they did not have a higher back injury claim
rate. Other races did not differ significantly from white persons for back
pain but persons of other races had a higher back injury claim rate. Similarly,
results for job satisfaction and smoking differed by outcomes. Poor job satisfaction
was significantly associated with increased risk of back pain but not with
a higher back injury claim rate. Current smokers had higher risk for back
injury claims and former smokers had higher risk for back pain.
There was no statistically significant difference for the preplanned
comparison of back injury claim rates among the 13,873 employees identified
by store management as involved in material-handling tasks prior to the interview
process. Stores with a belt requirement had 236 material-handling back injury
claims among 16.1 million work-hours for a crude incidence rate of 2.94 per
100 FTEs. Stores with voluntary belt use had 203 material-handling back injury
claims among 12.5 million work-hours for a crude incidence rate of 3.26 per
100 FTE (RR, 0.90; 95% CI, 0.75-1.09). Additionally, we found no effect of
the belt-requirement store policy among those interviewed for either back
injury claims (RR, 0.94; 95% CI, 0.70-1.28) or back pain (OR, 1.06; 95% CI,
No statistically significant effects of back belts were found among
the subgroup of employees who had no history of previous back injury, using
regressions with the same covariates shown in Table 2. Back pain was not different between those who reported
belt wearing usually every day and those who reported never wearing a belt
(OR, 0.98; 95% CI, 0.82-1.17), and the back injury claim rate was not different
for these groups (RR, 1.34; 95% CI, 0.91-1.98). Among the subgroup who had
a previous history of back injury, there were no effects of belt wearing on
back pain (OR, 0.90; 95% CI, 0.65-1.25), or back injury claim rate (RR, 0.92;
95% CI, 0.47-1.79).
Back belt use may be considered as a measure of compliance with store
policy, so an interaction term between belt wearing and store policy was examined
for the models shown in Table 2.
This interaction term shows that there is no effect of back belts when comparing
employees who reported belt wearing usually every day in stores that required
belt use with those employees who reported never wearing a belt in voluntary
belt-use stores for back pain (OR, 1.07; 95% CI, 0.89-1.29) or for back injury
claims (RR, 1.19; 95% CI, 0.79-1.78).
Back belt use is affected by store policy, so to assess the possibility
that a model including both covariates might introduce excess error, the store
policy covariate was removed from the regression models shown in Table 2. Back pain was not different between
those who reported belt wearing usually every day compared with those who
reported never wearing a belt (OR, 0.99; 95% CI, 0.85-1.14), and the back
injury claim rate was not different for these groups (RR, 1.20; 95% CI, 0.87-1.65)
after removing the store policy covariate.
No statistically significant effects of belt wearing were found among
a subgroup who reported consistent belt wearing habits on both the baseline
and follow-up interviews. Using the same covariates shown in Table 2, regressions were used to compare employees who reported
in both interviews wearing belts usually every day with those who reported
in both interviews never wearing a belt. There was no evidence that wearing
back belts reduced back pain (OR, 0.88; 95% CI, 0.73-1.07) or back injury
claims (RR, 1.57; 95% CI, 0.98-2.50) in these groups that reported consistent
To focus on those employees who frequently lifted heavier loads, regressions
were restricted to the subgroup of employees with the most strenuous job.
Using the same covariates as shown in Table
2, for an analysis restricted to receiver/unloaders, back pain was
not different between those who reported belt wearing usually every day compared
with those who reported never wearing a belt (OR, 0.81; 95% CI, 0.58-1.14),
and the back injury claim rates appeared to be the same for these groups (RR,
1.53; 95% CI, 0.82-2.84).
To assess the potential for selection bias, the effects of belt wearing
on back injury claim rates were compared among employees who completed a follow-up
interview and those who did not complete a follow-up interview. The crude
back injury claim rate among the 3066 employees who completed a baseline interview
but did not complete a follow-up interview (5.04 per 100 FTE; 95% CI, 3.88-6.44)
was nearly twice the crude back injury claim rate compared with the 6311 employees
who completed both interviews (2.61 per 100 FTE; 95% CI, 2.19-3.09). However,
there was no significant difference in back injury claim rates comparing those
who reported wearing belts usually every day with those who reported never
wearing them among those who did not complete a follow-up interview (RR, 0.97;
95% CI, 0.53-1.85) and among those who completed a follow-up interview (RR,
1.37; 95% CI, 0.91-2.05) in multivariable Poisson regressions. In another
evaluation of potential selection bias, the effects of belt wearing on the
prevalence of back pain were estimated using the baseline interview data as
in a cross-sectional study. In a multivariable logistic regression there was
no difference in the prevalence of back pain at baseline comparing those who
reported wearing belts usually every day with those who reported never wearing
them (OR, 1.07; 95% CI, 0.94-1.21).
The NIOSH prospective cohort study of back pain and back injury claims
in 9377 employees, controlling for multiple individual risk factors, found
no evidence to support the use of back belts as a preventive measure. We found
no effects of belt wearing in various subgroups: employees with and without
a history of previous back injury, employees with consistent self-reported
belt wearing habits from baseline to follow-up interviews, and employees with
the most strenuous job. Among 13,873 material-handling employees in 160 stores,
we found no difference in unadjusted back injury claim rates comparing a belt-requirement
store policy to a voluntary belt-use store policy.
Previous studies have relied on worker compliance to a store policy
to determine belt-wearing habits.9- 11
Accurate determination of workers' actual workplace belt-wearing habits is
a recognized limitation of these studies. By directly interviewing employees
about their belt-wearing habits, our study more closely measures typical belt
use in the workplace rather than implied belt use based on store policy.
A recent study in California over a 6-year period found a higher injury
rate during the months preceding the implementation of a mandatory back belt-use
policy than during the months after the policy was implemented (RR, 1.52;
95% CI, 1.36-1.69).12,13 In this
historical cohort study, estimates of back-belt effects were based on aggregate
back injury claim rates without controlling for multiple individual risk factors.
The NIOSH study was prospective with concurrent comparison groups, evaluated
both back injury claim rates and self-reported low back pain and controlled
for well-known back injury risk factors.
The potential effects of selection bias on the back pain results, due
to the inability to complete follow-up interviews on all employees who had
a baseline interview, is a limitation of our study. Ancillary analyses do
not demonstrate that selection biases alter the main conclusions of this study.
Other analyses of subgroups of employees and interaction effects attempted
to discover belt effects among groups of employees who were most likely to
be affected by belt wearing. However, even these comparisons failed to find
any back-belt effects.
Our study evaluates back belts using a prospective design in new stores
distributed over a wide geographic region, concurrent comparison groups, comprehensive
individual interviews, detailed exposure information, a job satisfaction measure,
multivariable regression analysis, and sufficient sample size. This study
considered 2 outcomes: the incidence of back pain and workers' compensation
claims for material-handling back injury requiring medical care. Adjustment
for multiple risk factors was incorporated in our investigation, especially
a history of previous back injury and lifting frequency, which has been lacking
in some previous studies on the effects of back belts. This is the largest
prospective study to date of material-handling workers with individual data
on back-belt use, back pain, and important confounders. Results based on these
multiple analyses of data all converge to a common conclusion: back-belt use
is not associated with reduced incidence of back injury claims or low back
pain in material handlers.