A Prospective Study of Back Belts for Prevention of Back Pain and Injury
Summary Statement
Reports of a study of back-belt use as it relates to back injury claims which found that there was no significant correlation between belt wear and reduction in claims
December 6, 2000
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 6 1 /2 months.
Participants A referred sample of 13873 material handling employees
provided 9377 baseline interviews and 6311 (67%) follow-up interviews;
206 (1.4%) refused baseline interview.
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.
JAMA. 2000;284:2727-2732
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 279507 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.
Methods
Study Design
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.
Data Collection
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.
Job Titles
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 study 6 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 stock-ERs,
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
Back Belt Use
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 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.
Back Belt
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, Ph.D., et al, unpublished
data, 1998) and physiology effects (Thomas G. Bobick, Ph.D., 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.
Back Pain Data
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.
Injury Claims
Data
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.
Statistical Methods
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 StatXact.8
Results
There were a total
of 144469 employees who worked in the 160 stores during the study period.
Of these, 13873 (10%) were identified by store management as involved
in material handling tasks prior to the interview process (FIGURE).
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 6 1 /2 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 every day.
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.
____________________________________________________
* Data are presented as number (percentage) of subjects in each column
unless otherwise indicated. Row categories are not mutually exclusive.
Row total of 8358 is less
than the number of completed interviews (n=8377) because of missing values.
New stores vs newly expanded
stores (see "Methods" section).
To convert to pounds divide
by 0.45.
f1 Row total of 6299 is less than the number of completed interviews (n
= 6311) because of missing values.
____________________________________________________
There was no statistically significant difference for the preplanned comparison of back injury claim rates among the 13873 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, 0.92-1.22).
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 co-variates 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 belt-wearing habits.
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).
____________________________________________________
* Interview responses are based on 6311 total follow-up interviews. Some
respondents did not answer all the questions.
Logistic regression model
with binary response outcome of pain reported at follow-up interview among
6311 employees. Estimates are adjusted for all other variables in this
Table. Because of missing covariate values, 6011 observations were used
for the multivariate model 'CI' indicated confidence intervals.
Denominators in million
worker-hours exposure are rounded to 2 decimal places. Rate per 100 full-time
equivalents (FTEs) is per 200000 work hours.
Poisson regression model
using back injury counts and work-hours among 9377 employees with a baseline
interview, estimates adjusted for all other variables in this Table.
f1 To convert to pounds divide by 0.45.
____________________________________________________
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).
Comment
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 13873 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.
Author/Article Information
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.
Corresponding Author and Reprints: James T. Wassell, PhD, Centers
for Disease Control and Prevention, National Institute for Occupational
Safety and Health, Division of Safety Research, 1095 Willowdale Rd, Morgantown,
WV 26505. (e-mail: jtw2@cdc.gov).
Acknowledgment: We thank the efforts of Jennifer L. Bell, PhD,
Guang X. Chen, MD, and David K. Hilling for analytical support; William
Halperin, MD, Roslyn A. Stone, PhD, Lawrence J. Fine, MD, Kyle Steenland,
PhD, Nancy A. Stout, EdD, and James W. Collins, PhD, for administrative
and/or scientific contributions; Thomas K. Hodous, MD, Harvey Checkoway,
PhD, Barbara Silverstein, PhD, Ellen Eisen, ScD, and Laura Punnett, ScD,
for critical review; Nancy J. Roder, MS, Louis D. Smith, MSEE, Linda L.
Morton, MS, Martin S. Forde, ScD, Susan Moir, MS, and Ninica L. Howard,
MS, for other support.
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