Lumbar Trunk Muscle Endurance Testing: An Inexpensive
Alternative to a Machine for Evaluation
Toshikazu lto, RPT, Osamu Shirado, MD, PhD, Hideki Suzuki, RPT, Masaaki Takahashi, MA, RPT,
Kiyoshi Kaneda, MD, PhD, Thomas E. Strax, MD
A B S T R A C T . Ito T, Shirado O, Suzuki H, Takahashi M,
Kaneda K, Strax TE. Lumbar trunk muscle endurance testing:
an inexpensive alternative to a machine for evaluation. Arch Phys
Med Rehabil 1996;77:75-9.
Objectives: The goals of this study were to verify the reliability and safety of new methods for evaluating trunk muscle endurance, and to compare the differences between healthy subjects
and patients with chronic low-back pain.
Design: Randomized and controlled study.
Setting: A referral center and institutional practice, and outpatient care.
Subjects: Ninety healthy subjects (37 men and 53 women
average age 46.2 years) and 100 patients with CLBP (40 men
and 60 women; average age 45.3 years) participated in this study.
Main Outcome Measures: During trunk flexor and extensor
endurance tests, the subjects were asked to maintain the original
positions for as long as possible. The performance time (seconds)
for which subjects could maintain the position was compared
between two groups, Test-retest correlation (r) was also analyzed.
The degree of lumbar lordosis was compared in conventional
and new methods.
Results: All test-retest correlations were significantly high in
both groups (p < .01). The performance time was much longer
in the healthy subjects than in the patients with CLBP during
any procedures (p < .01). Lumbar lordosis was significantly less
in our method than in the Kraus-Weber test (p < .01).
Conclusions: This study demonstrated that our methods for
measuring trunk flexor and extensor endurance had high reliability, reproducibility, and safety, and were easy to perform, with
no need for special equipment. This study also showed that trunk
muscles in patients with CLBP were more easily fatigued, compared with those in healthy subjects.
© 1996 by the American Congress of Rehabilitation Medicine
and the American Academy of Physical Medicine and Rehabilitation
M P A I R E D F U N C T I O N of trunk muscles is closely related
to pathogenesis of chronic low-back pain (CLBP)] -8 Researchers have intensively investigated trunk muscle function,
I
From the Divisionof Physical Therapy and Departmentof Orthopaedic Surgery
(Mr. Ito, Dr. Shirado, Mr. Suzuki, Dr. Kaneda), Hokkaido University Hospital,
and the Department of Physical Therapy, College of Medical Technology (Mr.
Takahashi), Hokkaido University,Sapporo, Japan; and the Departmentof Rehabilitation Medicine, JFK Johnson Rehabilitation Institute (Dr. Strax), UMDNJ-Robeft Wood Johnson Medical School, Edison, NJ.
Submitted for publication November 15, 1994. Accepted in revised form July
5, 1995.
Presented in part at the 21st Annual Meeting of the International Society for
the Study of the Lumbar Spine, June 21-25, 1994, Seattle, WA.
No commercial party having a direct financial interest in the results of the
research supporting this article has or will confer a benefit upon the authors or
upon any organization with which the authors are associated.
Reprint requests to Osamu Shirado, MD, PhD, Department of Orthopaedic
Surgery, Hokkaido University School of Medicine, Kita-15 Nishi-7, Kita-Ku,
Sapporo 060, Japan.
© 1996by the AmericanCongress of RehabilitationMedicineand the American
Academy of Physical Medicine and Rehabilitation
0003-9993/96/7701-330653.00/0
which can be described in terms of strength, endurance, and
speed. 9 Muscle endurance can be defined as the ability to produce work over time or the ability to sustain effort. 9 Decreased
endurance seems to be one of the significant risk factors in the
development and incidence of CLBP. ~0Thus, many studies have
been performed to evaluate characteristics of endurance in patients with CLBP by using various methodologies. 4'1°-]4
Although there are no gold standards to measure trunk muscle
endurance, two of the most popular methods are the KrausWeber test for flexors ~5 (figs 1A through 1C) and the SCrensen
test for extensors ~° (fig 1D). During each test, subjects in supine
and prone positions are asked to maintain their trunk and lower
extremities in a certain position. Although both tests have been
accepted in clinical situations, there are some disadvantages for
use in patients with CLBP. First, lumbar lordosis increases during these procedures because of extended hip and knee joints, j
A hyperextended lumbar spine can produce bulging of the intervertebral disc and buckling of the ligamentum flavum, followed
by the narrowing of the intervertebral foramen, j']6 As a result,
low-back pain can occur or be aggravated by hyperextending
the lumbar spine. ]'~6Many authors suggest avoiding hyperextension of the lumbar spine during trunk muscle exercises. 1'16 It is
our belief that this position should be avoided even for short
time periods for evaluating endurance. Second, overloading on
the lumbar spine may occur during these procedures. This can
induce or worsen low-back pain in the patient with CLBP.
Moreover, we often found that patients could not even set these
postures before starting evaluation, because of overloading.
Third, objective values in these tests remain unclear. ~7Researchers have tried to find objective techniques for assessing trunk
muscle endurance with a variety of machines: Electromyography (EMG) frequency analysis jT'j8 and computerized dynamometers. 433 The major disadvantages of these machines, however,
are that they are time-consuming and expensive. 9'19
We, therefore, developed a new method based on the KrausWeber and Scrensen endurance tests to overcome these disadvantages.
The goals of this study were threefold: to introduce our methods for measuring trunk muscle endurance, to verify their reliability and safety, and to compare the differences between
healthy subjects and patients with C L B P by using these methods. In terms of the safety of the methods for measuring trunk
muscle endurance, this implies that the lumbar lordosis can be
reduced and overloading can be avoided during the test. In other
words, low-back pain in any subjects should not be worsened
by increasing the lumbar lordosis and providing overloading to
lumbar spine.
MATERIALS AND METHODS
Subjects
There were 190 subjects included in this project. Ninety
healthy subjects, 37 men and 53 women, volunteered as the
control group. They were recruited through the authors' personal relationships and word of mouth, and were chosen in a
similar age range as the C L B P subjects. All healthy subjects
Arch Phys Med Rehabil Vol 77, January 1996
76
A~25 °
LUMBAR TRUNK MUSCLE ENDURANCE, Ito
B
to analyze the test-retest correlation. The second test was performed 72 hours after the first one.
Radiographic Analysis
C
D
Fig 1. Conventional methods for evaluating trunk muscle endurance. (A,
B, C) Kraus-Weber test for trunk flexors; (D) Sorensen test for trunk
extensors. The former consists of three different tests to evaluate different muscles: (A, B) upper and (C) lower parts of abdominal muscles. The
latter is only one procedure in which subjects in a prone position are
asked to maintain the upper body in a horizontal alignment while firmly
strapped to the table over the pelvis, thigh, and lower leg. The time
(seconds) for which subjects could maintain the position is evaluated,
had no history of low-back pain and were well motivated in
this study. Ages ranged from 35 to 49 years, with a mean age
of 46.2 years. One hundred patients with CLBP, 40 men and 60
women, were studied. They were recruited from the outpatient
clinics in some hospitals where the authors practiced. Selection
criteria included: (1) primary low-back pain without sciatica
and neurological deficits, lasting at least 6 months; (2) no history
of low-back surgery, (3) radiological findings of slightly or
moderately degenerative changes without any gross spinal pathology such as tumor, infection, osteoporosis, spondylolysis,
and spondylolisthesis; and (4) no involvement with workers'
compensation, litigation, or disability insurance. Ages ranged
from 33 to 48 years, with a mean age of 45.3 years. Regarding
the origin of the CLBP, 22 patients had an episode such as
twisting and lifting. Insidious onset was in 41 patients, and
unclear in 37.
According to a 1-10 visual analogue pain scale, ratings were
less than 6 in all the patients. In other words, patients' lowback pain was slight to moderate. In terms of functional performance, all patients were independent without aids or assistance
during activities of daily living. No patients took any medication
in the week preceding the experiment.
Informed consent was obtained from all of the subjects and
the procedure for this project was reviewed by an Institutional
Review Board.
Lateral radiographs of the lumbar spine were taken on 10
randomly selected healthy subjects to assess the degree of lumbar lordosis during the conventional Kraus-Weber test (fig 1A)
and our flexor-endurance test (fig 2A). The distance between
the X-ray tube and the film was kept constant at 2m to minimize
errors in radiographic measurements. ~6'2°The degree of lumbar
lordosis was measured as the angle between the upper endplates of the L1 and S1 vertebrae, as described previously.2°
Statistical analysis was carried out using a paired t test. Pearson correlation coefficients were also obtained.
RESULTS
In terms of body weight and height, there were no significant
differences between the groups (table 1). Occupations were similar for both groups. None of them were participating in any
weight-training exercise, such as back or abdominal strengthening programs. All 190 subjects completed this study without
any problems. None of the patients experienced worsened lowback pain in this project.
Test-Retest Correlation
Table 2 shows the test-retest correlation and the intraclass
correlation coefficients in both procedures. In the flexor endurance test, the test-retest correlation (r) was .95 and .89 for the
healthy men and women, and was .91 and .85 in the CLBP men
and women, respectively. In the extensor endurance test, r was
.97 and .94 for the healthy men and women, and was .93 and
.95 for the CLBP men and women, respectively. All test-retest
Procedures and Measurements
For evaluating flexor endurance, subjects were asked to lie
in a supine position and to raise the lower extremities with 90 °
flexion of the hip and knee joints (fig 2A). For measuring extensor endurance, subjects were asked to lie in a prone position
while holding the sternum off the floor (fig 2B). A small pillow
was placed under the lower abdomen to decrease the lumbar
lordosis.2° During both procedures, subjects were asked to maintain their maximum flexion of cervical spine, with pelvic stabilization through gluteal muscle contraction. These cervical and
pelvic alignments proved to be the most optimal posture not
only for decreasing the lumbar lordosis, but also for activating
trunk flexors and extensors most effectively,z°
During both tests, the subjects were asked to maintain the
original positions for as long as possible, not exceeding a 5minute time limit. The performance time (seconds) for which
subjects could maintain the position was compared between the
two groups. Each procedure was performed twice in all subjects
Arch Phys Med Rehabil Vol 77, January 1996
Fig 2. Our methods for measuring trunk muscle endurance. (A) The test
for flexors, and (B) the test for extensors. The performance time of both
groups was compared. Although the exact amount of cervical flexion
might have been different between both tests, the subjects were asked
to maintain their maximum flexion of cervical spine while contracting
the gluteal muscle.
77
LUMBAR TRUNK MUSCLE ENDURANCE, Ito
Table 1: Description of the Healthy Subjects and CLBP Patients
Healthy Subjects
(n = 90)
Men
Number (n)
Age (yr)
Mean
Range
Weight (kg)
Mean
Range
Height (m)
Mean
Range
Women
CLBP Patients
(n = 100)
Men
Women
37
53
40
60
44.3
35-47
46.8
37-49
44.9
33-46
45.9
36-48
64
54-78
57
56-72
66
56-80
62
59-70
1.72
1.56-1.76
1.63
1.54-1.70
1.73
1,60-1.78
1.62
1.53-1.72
correlations for the corresponding endurance measurements
were significantly high in both groups (p < .01). All correlation
values were more than 0.9, except in the flexor endurance test
in the females.
First, the procedure should be easy to perform in a clinical
situation, and special equipment should be unnecessary.9 Because of advanced technology, a variety of isokinetic dynamometers are commercially available to investigate the trunk muscle
function in sagittal and coronal m o t i o n . 5'7'2f'22 The major units
among them are computerized and easy to deal with under
clinical and experimental situations. These devices produce a
large amount of computerized measurements that combine a
vast array of parameters relating to force, work, power, endurance, and their arithmetic variations, such as the mean and peak.
Thus, there are many advantages for using these machines to
evaluate patients with CLBP. However, one of the major disadvantages is the cost of equipment.9'~9 Some machines are so
expensive that many hospitals and institutions cannot afford
to pay for them. Therefore, it is desirable for clinicians and
investigators to find an alternative to such expensive machines.
Second, the procedure should be safe for any subject. Postures to avoid increasing lumbar lordosis should be selected for
A
Performance Time in Both Procedures
Figure 3 shows the performance time during both procedures.
The time was much longer in the healthy subjects than in the
patients with CLBP during any procedures (p < .01). During
the flexor endurance test in the males, the mean value was 182.6
_+ 69.3 and 107.9 + 49.6 seconds in the controls and patients,
respectively. During the extensor endurance test in the males,
the mean value was 208.2 + 66.2 and 85.1 ___55.6 seconds in
the controls and patients, respectively. During the flexor endurance test in the females, the mean value was 85.1 _+ 44.8 and
57.2 -+ 33.2 seconds in the controls and patients, respectively.
During the extensor endurance test in the females, the mean
value was 128.4 + 53.0 and 70.1 + 51.8 seconds in the controls
and patients, respectively.
In terms of a maximum duration during the tests, no subjects,
with the exception of the following, were able to achieve more
than 5 minutes: four healthy males in the flexor endurance test
and 10 healthy males in the extensor endurance test. No patients
were able to continue the tests more than 5 minutes.
Lumbar Lordosis During Flexor Endurance Testing
The mean lumbar lordosis was 48.3 + 5.7 and 25.4 _+ 2.5
degrees during the conventional Kraus-Weber test and our
method, respectively (fig 4). Lumbar lordosis was significantly
less in our method than in the Kraus-Weber test (p < .01).
DISCUSSION
The major purpose of this project was to verify the reliability
and safety of our methods for evaluating the trunk muscle endurance, and to compare the difference between healthy subjects
and patients with CLBP by using these methods. From a clinical
point of view, there seems to be several requirements for evaluating trunk muscle endurance.
300
200
100
Flexors
B
Extensors
300
•
..........................................................................................[ ]
HEALTHY
CLBP
1
.....
200
T
Q}
E
100
Table 2: Test-Retest Correlation (r) and Intraclass Correlation
Coefficients (ICC) in Both Procedures
Correlation Coefficient (Pearson)
M e n (n = 77)
Flexors
Healthy
CLBP
Extensors
Healthy
CLBP
* p < .01
W o m e n (n = 113)
ICC
Flexors
.95"
.91"
.89*
.85*
.95*
.90*
.97"
.93*
.94"
.95*
.97"
.93*
Extensors
Fig 3. Performance time (seconds) for which subjects could maintain the
original position (shown in Fig 2) during trunk muscle endurance testing.
(A) Men, (B) Women. The error bars indicate the standard deviation (SD);
p < .01. The performance time was much shorter in the patients than
in the healthy subjects, which implied that the trunk muscle endurance
of the patients was significantly less than that of the healthy subjects,
Arch Phys Med Rehabil Vol 77, January 1996
78
LUMBAR TRUNK MUSCLE ENDURANCE, Ito
II). They found that patients with CLBP had a greater fatigability
501 ....................................
I.............................................................................................................. of the trunk flexors than did healthy controls. No differences
between the groups could be found in the trunk extensors. Biering-SCrensen ~° established and developed the Sorensen test to
evaluate the isometric endurance of the back muscles. She re4C
ported a 1-year prospective study that showed that good isometric
endurance of the back muscles might prevent occurrence of lowback trouble. ~° Nicholaisen and Jorgensen tJ evaluated the back
,~ 3C
muscle endurance with the SCrensen test. They pointed out that
the isometric endurance of the patients with severe low-back pain
was significantly less than that of the normal controls and the
patients with a slight low-back pain. Similar results were obtained
by using the Scrensen test. ~'~4
Some investigators have applied EMG to analyze trunk musE
cle endurance and fatigue. Anderson and colleagues23 studied
,,d 10
EMG RMS (root-mean-square) amplitude and power spectral
frequency shift simultaneously at several levels in the thoracolumbar spine. They concluded that there was a direct relationship between load application, increase in electrical activity as
measured by amplitude of RMS voltage, and shift in mean
Kraus-Weber
Our method
power spectrum. Thus, the relationship between initial application of spine load and decline in mean power frequency was
Fig 4. Lumbar lordosis during two different procedures for evaluating
well established in their study. Mayer and associates,24 however,
trunk flexor endurance (n = 10L The error bars also indicate the standard
found a nonlinear relationship between them and concluded that
deviation (SD); p < .01. Lumbar lordosis was significantly less in our
myoelectric signal analysis techniques were less promising as
method than in the Kraus-Weber test.
a clinical tool for use in endurance evaluation.
More recently, Mayer and Gatche113 used the more sophistitest procedures, because hyperextension of the lumbar spine can
cated machine (Cybex Trunk Extension Flexion Unit) and evalinduce or worsen low-back pain.~:6 Overloading during tests is
uated the endurance with decline curve in work output per
also harmful especially for patients with CLBP, because of
repetition over the trials. The data in patients with CLBP were
the possibility of causing low-back pain. One should carefully
easily and successfully compared with a normal database.13 The
consider the test procedures with the least risk factors.
current study demonstrated similar results to the previous studThird, high reliability and reproducibility are mandatory to
ies. The isometric endurance of abdominal and back muscles
be widely used for evaluating trunk muscle endurance. 9'~9Manof the patients with CLBP was significantly less than that of
ual tests seem to be lacking in objectivity when used for measurthe healthy subjects. As previously mentioned, however, aning muscle function. ~7'19
other issue we need to consider is strength. Further investigation
The current study demonstrated that our methods applied to
is needed to clarify the relationship between trunk muscle
healthy subjects and patients with CLBP could satisfy these
strength measured with a dynamometer, and trunk muscle enrequirements. Our methods can be performed anywhere and
durance evaluated with our methods.
anytime without any special or expensive equipment. The radioFive minutes was chosen as the maximum duration in our
graphic measurement to analyze the degree of lumbar lordosis
endurance tests. Although previous investigators ~°-~2selected 4
was performed only in the flexor endurance test. Because irradiminutes as the maximum duration in the extensor endurance
ation seemed to be a large ethical problem in healthy populatest, some healthy subjects could tolerate our test more than 4
tions, we wanted to minimize X-ray exposure. In fact, all the
minutes in the pilot study, thus we chose 5 minutes as the
healthy volunteers rejected the request of excessive irradiation
maximum duration in our project. No subjects, except a small
in this project. In spite of this limitation, the radiographic study
number of healthy men, in both groups could continue our
showed that our flexor endurance test was safe in terms of
endurance tests longer than 5 minutes. Although a time greater
decreasing lumbar lordosis. Although we could not take any
than 5 minutes for some of the healthy subjects may provide
radiographs in the extensor test, a small pillow placed under
more reliable results, the results of this project showed that 5
the lower abdomen successfully reduced the lumbar lordosis in
minutes as the maximum duration was sufficient to prove the
the prone position. ~6 This implies that our extensor endurance
significant difference between the two groups.
test can reduce the lumbar lordosis to some extent, though XIn conclusion, this study demonstrated that our methods for
rays are necessary to evaluate lumbar lordosis precisely.
measuring trunk flexor and extensor endurance had several adAll 190 subjects completed this study without any problems,
vantages. It has high reliability, reproducibility, and safety.
and no patients experienced worsened low-back pain in this
Moreover, it is easy to perform, its cost is low, and special
project. The safety of our tests was verified in terms not only
equipment is unnecessary. Lumbar lordosis was significantly
of reducing the lumbar lordosis but also of avoiding overloading
less during our test for flexor endurance than during the convenand preventing the worsening of low-back pain in the patients.
tional Kraus-Weber test. Our methods might be used as an
High reliability and reproducibility were proven with test-retest
alternative to a machine for evaluating trunk muscle endurance.
correlation. It is our belief that the procedures presented in this
This study also showed that trunk muscles in patients with
study comprise a useful test modality to evaluate trunk muscle
CLBP were more easily fatigued, compared with trunk muscles
endurance, not only in healthy subjects but also in patients with
in healthy subjects.
CLBP.
Trunk muscle endurance in patients with CLBP has been invesAcknowledgments: The authors thank R. P. T. Naho Sarashina and
tigated with various methods. Suzuki and Endo 4 evaluated fatigToyo Kikumoto for their assistance with the data collection, and Ms.
ability of trunk muscles using the isokinetic dynamometer (Cybex
Joan Goddard for her assistance with the preparation of this manuscript.
Arch Phys Med Rehabil Vol 77, January 1996
LUMBAR TRUNK MUSCLE ENDURANCE, Ito
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