Effects of Back Belt Application on Trunk Muscle Fatigue and Rating of Perceived
Exertion during Repetitive Lifting
Kanphajee Sornkaew1,*, Wattana Jalayondeja 1,#, Keerin Mekhora1
1
Faculty of Physical Therapy, Mahidol University, Nakhon Pathom, Thailand
*e-mail: kanphajee@outlook.com, #e-mail: wattana.jal@mahidol.ac.th
Abstract
Back belt has been introduced and increasingly used in manual handling activities for
several years. However, there is still unclear about the effects of back belt which may take a
role in preventing muscle fatigue. Muscle fatigue is one of the major causes of low back pain.
The purpose of this study was to investigate the effects of back belt application on localized
trunk muscle fatigue and rating of perceived exertion (RPE) trunk muscle fatigue during
repetitive lifting among non-low back pain persons. Six men and twelve women, between
twenty-one to thirty-three years, had no experiences of using back belts participated by
performing two sets of twelve-minute lifting with and without back belt application. One
hour for washing-period between each set was provided. Lifting frequency was twenty-five
times per minute. Lifted-weight was calculated by ten percent of participant’s body weight.
Lifting posture and back belt tightness were also controlled. Before and after each trial every
participant was required to rate their rating of perceived exertion (RPE) or overall body
exertion and filled-out localized muscle fatigue questionnaires. By using paired t-test, the
result was found that back belt application had significant effects on the different changes of
RPE and localized muscle fatigue. Back belt application can significantly decreases RPE
from 4.11 to 3.39 (0.72, 17.57%), Localized muscle fatigue from 5.65 to 4.71 (0.94, 16.67%)
and 5.65 to 4.76 (0.88, 15.63%) on paravertebral area of the lower back. (p-value <0.05).
Assuming that back belt may increase participants’ proprioceptive awareness and sense of
security. On the other hand the lack of strong rationale for the use of back belt based upon
ergonomic criteria should call into question to the recommended prescription of the devices
under the presumption of hazard control. Further studies in various aspects are suggested.
Keywords: BACK BELT, LIFTING, MUSCLE FATIGUE
Introduction
As a source of low back injury, lifting has always been used in daily activities as well
as implements various tasks. In Thailand, the Workmen’s Compensation Fund (WCF)
approved payment of compensation benefits for 149,436 employees with work-related
injuries or sickness. It was found that the illness caused by nature of work was injuries from
lifting heavy objects. [1] Many studies have tried to solve these problems by accessing via
different approaches to decrease the incidence of low back injury including lifting techniques,
exercise training, workstation ergonomic modification, back belt application, risk assessment
and selection of staffs that might be at risk in heavy lifting tasks also in matter of skills and
experiences. [2] Although each approach used different methods and principles, the main idea
is to design work practices that is under the threshold levels of discomfort, fatigue and injury.
[3]
In 2000 Hoogendoorn et al., published the results of their prospective cohort study on
trunk flexion and rotation during lifting at work are the risk factors of low back pain. The
study showed that the relation between working with the trunk flexion (≤ 60 degrees) and low
back pain was stronger than the relation between working with the trunk flexion (≤30
degrees) and low back pain. The relative risk for working with the trunk flexion (≤30
degrees) did not increase with increasing duration of exposure. [4] The lifting task is
characterized by increasing of trunk flexion and trunk bending torque [5] whereas the
activities that require cyclic lifting and lowering of a load are considered to be risk factors for
back injury. In the meantime of lifting trunk muscles have to develop a sufficient force to
provide adequate stability and prevent tissue failure of the spinal complex so muscle
activation must be optimally timed and order of sufficient magnitude to protect the structures
from injury during a lift. [6] The muscles fail in maintaining the required force is called
muscle fatigue. Two important factors that should be determined when designing a fatigue
study are fatigue induction, the type of exercise inducing fatiguing, and fatigue
quantification. [7] Muscle fatigue can be measured by physiological approach; there are two
characteristics of physiological fatigue. Rating of perceived exertion (RPE) is related to
generalize fatigue. Borg CR10 and Borg RPE scale [8] are commonly used to evaluate
overall and localized fatigue from exertion. Fatigue is an important functional parameter for
physical work and daily activities. [9]
Back belts and lumbosacral orthoses are designed to provide support to the lumbar
spine. Both of these devices function in a biomechanical similar manner by reducing trunk
range of motion, trunk stiffness, increasing intra-abdominal pressure and decreasing the force
required by the trunk muscles. [10] Previous studies have investigated the effects of
abdominal belts in many aspects such as in 1989, the effects of a belt on intra-abdominal
pressure during weight lifting were investigated by Harman et al. The back belt acted as the
resistance to abdomen and forced abdominal muscles to move inwardly while contracting.
The increased IAP may assist in maintaining the alignment of the intervertebral joints. [11] In
1999 Miyamoto and fellows evaluated the effects of abdominal belts on lifting performance,
muscle activation, intra-abdominal pressure and intra-muscular pressure of the erector spinae
muscles and found that intra-muscular pressure of the erector spinae muscles increased
significantly by wearing the abdominal belt during valsalva maneuvers and during maximum
isometric lifting exertions. [12] Furthermore, wearing abdominal belts raises intra-muscular
pressure of the erector spinae muscles and appears to stiffen the trunk. Assuming that
increased intra-muscular pressure of the erector spinae muscles stabilizes the lumbar spine,
wearing abdominal belts may contribute to the stabilization during lifting exertions.
In 2002 Kocharoan N. investigated the application of abdominal belt and the result of back
muscles exercise in lifting task. The study demonstrated that abdominal belt application
significantly reduced back muscular load similarly to back muscular load after receiving back
exercise training. Muscle activity, work capacity or work duration were not observed in this
study. [13] In 2003 Chen examined the effect of the tightness of the abdominal belt on the
determination of psychophysical lifting capacities by using external abdominal pressure to
determine the tightness of the belts. Four levels of tightness (no belt, 15, 20, and 25 mm Hg)
were evaluated while subjects were determining their maximal acceptable weights of lift
under various task combinations. The results indicated that the maximal acceptable weight of
lift significantly differed with the tightness of the belt. [14] The effects of back belt wearing
on trunk muscle fatigue were not monitored within these studies. The main purpose of this
study was to determine the effects of back belt application on trunk muscle fatigue and the
rating perceived of exertion during repetitive lifting tasks in non-low back pain persons.
Methodology
Eighteen healthy participants (six men and twelve women) ages of 21 to 33 years. A
full ethical approval was granted by the research ethics committees. The written informed
consent was obtained by each participant after full explanations of the experimental
procedures involved also the advantages and the possible risks of the study. Then participants
were screened for prior back problems, the presence of cardiovascular, orthopedic, or
metabolic problems. Descriptive statistics for the participants’ age, height, weight, and lifting
load are located in Table 1.Testing took place at the faculty of Physical Therapy, Mahidol
University, Thailand.
Table 1 Anthropometric Characteristics
Mean ±SD
Age (year)
27.78 ± 3.54
Height (m)
1.66 ± 0.08
Weight (kg)
56.33 ± 6.44
BMI (kg./m2)
20.48 ± 1.53
Lifting load (kg.)
5.64 ± 0.67
Procedure
Prior to the test every participant chose between task A and task B. They were not
allowed to know the assigned tasks. Task A was a lifting without back belt application, task B
was a lifting with back belt application. Participant lifted a 25 x 32 x 29 cm box with handles.
For their safety their lifting load was calculated by 10% of participants’ body weight. Lifting
excursion was from knee to waist level. An adjustable shelf was individually adjusted to
participants’ height by having the participants standing on the floor at a comfortable distance
away from the shelf with knees fully extended, back straight, both arms extended. The
researcher marked their footprints. The researcher adjusts the adjustable shelf as participants’
knee level to control the range of trunk flexion to be within safety zone (<30º from vertical
line). The starting position the participants reached both arms out forward with elbow fully
extended holding the box by its handles. A metronome was used to pace the task at 15 cycles
per minute. Participants performed lifting and lowering task continuously for 12 minutes. At
before, 3rd, 6th, 9th and 12th minute of lifting test participants were asked to rate their rating of
perceiving exertion from 0 to 10 (0 indicated “not feeling exhausted at all” and “10 indicated
feeling extremely exhausted could not continue performing the task no more”). Fatigue
questionnaire was used immediately before and after completed 12 minutes lifting test.
Fatigue questionnaire was a body chart which had 17 divided areas on trunk. Participants
rated their feeling of localized muscle fatigue from 0 to 10 (0 indicated “not feeling localized
muscle fatigue on that divided area at all” and 10 indicated “feeling extremely localized
muscle fatigue and could not continue performing the task no more”) Figure 1. In order to
perform task B every participant was required to wear back belt, the level of tightness of
back belt was 10 mmHg allowed the participants to feel comfortable, [15] before performing
a 12 minutes lifting task. Two trials were separated by a minimum of an hour to allow
recovery time. [16]
Data processing
All rating of perceived exertion and localized muscle fatigue questionnaire data were
collected. The different means of localized muscle fatigue questionnaire were calculated by
using the different changes between pre-test and post-test. Afterward the different means of
each lifting, with and without back belt application, were compared within the same
participant.
Statistical analysis
Data analyses were performed by using the SPSS windows version. The level of
statistical significance was set at probability level less than 0.05 (p<0.05) for all analyses.
The results were expressed as means and standard deviations. Paired t-test was used to
compare the mean differences within the same person.
Results
Eighteen non-low back pain participants were recruited. None of them had any
experiences in manual handling work. All parameters from this study were age, body weight,
body mass index were shown in Table 1. Fatigue questionnaire was a body chart which had
17 divided areas on trunk Figure 1.
Figure1. Seventeen areas of localized muscle fatigue questionnaire
The frequencies of localized muscle fatigue on each area were given from 18 participants
were shown in Figure2.
Figure2. The frequency of Localized muscle fatigue on each area
Figure3. Localized muscle fatigue scores reported by 18 participants
The result was found that back belt application had significant effects on the different
changes of localized muscle fatigue from 5.65 to 4.71 (0.94, 16.67%) and 5.65 to 4.76 (0.88,
15.63%) on paravertebral area (area11 and area 12) of the lower back (P-value <0.05)
Furthermore back belt application decreases the different changes of RPE from 4.11 to 3.39
(0.72, 17.57%) Table2.
Table2. Effects of back belt application were tested by paired t-test analysis.
Mean
RPE NB- WB
LMF NB Area11 – WB Area 11
LMF NB Area12 – WB Area 12
.722
.941
.882
Paired Differences
Std.
95% CI of the
S.D Error
difference
Mean Lower
Upper
.669 .158
.389
1.055
.639 .151
.623
1.259
.758 .179
.505
1.259
t
df
4.579
6.249
4.939
17
17
17
p-value
(2Tailed)
0.00
0.00
0.00
Discussion and Conclusion
Localized muscle fatigue
All participants (n=18) reported localized muscle fatigue on paravertebral areas which
were area11 and area12. The frequency of muscle fatigue also presented on the other areas;
10 participants indicated muscle fatigue on area10 and area13 (lateral side of back), in both
tests, 2 participants indicated muscle fatigue on area 4-6, 14 – 17 during lifting with back
belt. 2 participants indicated muscle fatigue on area 4-6, 9 and 14 during lifting without back
belt.
The present study found the decrease of number of participants who had reported
fatigue on back area from 5.65 to 4.71 and from 5.65 to 4.76 after wearing back belt. The
results of this study show that back belt application has significant results in different changes
of localized muscle fatigue which may suggest that the use of back belts reduces lumbar
paraspinal muscle fatigue that may reduce lower back pain incidents. This finding supports
previous studies that back belt application may reduce trunk muscles force by increasing IAP
and decreasing in trunk muscles activities. It is possible that back belt application can reduce
trunk muscle fatigue. [17-20] This supports previous studies that trunk extensor muscle
activity maybe reduced through the intra-abdominal pressure mechanism. [21-23]
Arjmand and Shirazi-Adi indicated that back belt application can raise intra-abdominal
pressure which unloads the spine in standing and flexion tasks even generates back muscle
forces. [24] The biomechanical factors of back belt were also discussed in many studies in
terms of force reduction and changes in body posture. [12, 25-29] One study reported that the
positive effects of back belt wearing in back muscle load was shown in an increase of IAP
and decrease of back muscle activities. [10] The limited range of motion (ROM) by back
belt, several studies report decreased trunk motion in lifting task with back belt. By wearing
back belt had changed the pattern of motion and reduced the amount of flexion in comparison
with not wearing a support during lifting. [30] Granata et al. reported that while wearing belt
the activity of the left erector spinae was reduced by 4% of maximum voluntary contraction
(MVC) and the activity of the rectus abdominis was reduced while the activity of the left
internal oblique was increased. [10]
Rating of perceived exertion
It was found that RPE range of lifting with back belt application (3.39±1.85) is lower
than RPE of lifting without back belt (4.11±1.96); 11 persons reported the decrease of RPE in
lifting with back belt application meanwhile 7 persons reported no differences of RPE
between back belt and non-back belt application.
Assuming that the stiffness of back belt can make participants to feel more secure
during lifting; therefore, participants can lift with more confident and easily with back belt
rather than lifting without back belt. The authors also reported that the use of lifting belts
transferred the motion from the back to the pelvis. The redistribution of muscle forces could
occur while wearing back belt. The elastic belt covered along the pelvis and the thoracic
region of the spine providing greater resistance to trunk flexion. The participant might use
more pelvic tilt rotation than lumbar rotation while lifting with back belt. These studies
concluded that effect of limited ROM by back belt may cause trunk stiffness. This stiffness
can allow participants to feel more secured during lifting with back belt. But there are still
many controversies about the effect of back belt on RPE. In 1989, Rabinowitz et al., studied
the effect of back belts on the spinal shrinkage, heart rate, perceived exertion, and regional
body pain. They reported that neither the lifting technique nor the use of the belt had a
significant effect Heart rate as well as regional body pain was not affected by the use of the
belt. Perceived exertion values were 11.35 and 11.50 for lift with and without belt,
respectively. [31] Furthermore, The psychophysical approach may not be an appropriate
technique to assess the back belt’s effect due to the Hawthorne effect. The results suggested
that back belt may increase the perceived stability of the trunk. Alterations in afferent and
efferent stimuli from somatosensory system may occur such that the participants feel more
secure while wearing a back belt. These sensations could arise from cutaneous, muscle and/or
joint sensor of the trunk. Another study of placebo, back belts and Hawthorne effect
suggested that 35.2±2.5% of persons in placebo studies get relief and holding the breath has
the better effect on intra-abdominal pressure than back belt. As lifting situation, it is difficult
to justify the distribution of back belts. [32-36] RPE is moderated by psychological factors
(cognition, memory and previous experience and understanding of the task) and situational
factors (knowledge of the end point, duration, temporal characteristics of the task. In
additional the influences of motivation for exercise can be expected to link with RPE . To
decrease the variance in RPE from motivation, the recruitment of trained participants is
recommended. [32]
Conclusion
Assuming that back belt may increase participants’ proprioceptive awareness and sense of
security. On the other hand the lack of strong rationale for the use of back belt based upon
ergonomic criteria should call into question to the recommended prescription of the devices
under the presumption of hazard control. The decision to prescribe belts to employees in the
workplace should be at the discretion of an adequately trained occupational health care
provider. These devices should not be provided as an alternative to appropriate administrative
and/or engineering controls.
Recommendations for Future Studies
It is recommended that further well-controlled, prospective, randomized clinical trials are
necessary to evaluate the effectiveness of back belts as personal protective equipment. The
study should focus on how the back belt application affects skeletal muscle properties and
biomechanics changes during fatigue occur.
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