Clinical Rehabilitation 2007; 21: 640–647
Sensitivity, specificity and predictive value
of the clinical trunk muscle endurance tests
in low back pain
Amir Massoud Arab, Mahyar Salavati Department of Physical Therapy, University of Social Welfare and Rehabilitation
Sciences, Evin, Ismaeil Ebrahimi Faculty of Rehabilitation, Iran University of Medical Sciences and Mohammad Ebrahim
Mousavi Orthopaedics, University of Social Welfare and Rehabilitation Sciences, Evin, Tehran, Iran
Received 1st August 2006; returned for revisions 28th November 2006; revised manuscript accepted 10th December 2006.
Objective: To describe the sensitivity, specificity, positive predictive value,
negative predictive value and diagnostic accuracy of five clinical tests used to
measure trunk muscle endurance in low back pain.
Design: A cross-sectional non-experimental design.
Setting: Orthopaedic and physical therapy departments of four hospitals and
outpatient physical therapy clinics, Tehran, Iran.
Subjects: Convenience sample of 200 subjects participated in this study.
Subjects were categorized into four groups: men without low back pain (N ⫽ 50,
mean (SD) age ⫽ 38 (12) years), women without low back pain (N ⫽ 50, mean
(SD) age ⫽ 43 (11) years), men with low back pain (N ⫽ 50, mean (SD) age ⫽ 39
(12) years) and women with low back pain (N ⫽ 50, mean (SD) age ⫽ 43 (12)
years).
Main measures: Five clinical static endurance tests of trunk muscles such as:
Sorensen test, prone isometric chest raise test, prone double straight-leg raise
test, supine isometric chest raise test and supine double straight-leg raise test
were measured in each group.
Results: The result of receiver operating characteristics (ROC) curve analysis
revealed that in a separate analysis of data for men and women, among all tests,
the prone double straight-leg raise test had the highest sensitivity, specificity and
predictive value in low back pain compared with other performed tests.
Conclusions: It seems that the prone double straight-leg raise test has more
sensitivity, specificity and predictive value in low back pain than other tests and
could be used as a useful clinical method for testing the spinal muscle
endurance to predict the probability of the occurrence of low back pain.
Introduction
Low back pain is one of the most common and costly
musculoskeletal complaints in today’s societies,
Address for correspondence: Amir Massoud Arab, Department of
Physical Therapy, University of Social Welfare and Rehabilitation
Sciences, Evin, Koodakyar Ave., PO Box 19834, Tehran, Iran.
e-mail: arabloo_masoud@hotmail.com
© 2007 SAGE Publications
affecting up to 70–80% of the population with at least
one episode during their lifetime.1–3 Despite its high
incidence and detrimental effects on individuals’
activities the exact causes of mechanical low back
pain have not yet been fully understood as no
approach to diagnosis or treatment has been shown to
be clearly effective.4,5 In recent decades the main
focus has been placed on trunk muscle endurance and
its association with low back pain. The back extensor
10.1177/0269215507076353
Clinical trunk muscle endurance tests
muscles are considered to be postural muscles that aid
in maintaining upright standing posture and controlling lumbar forward bending.6 Numerous studies have
shown a significant decrease in back extensor muscle
endurance in patients with low back pain.7–11 It has
been reported that evaluation of the endurance of
trunk extensor muscles has greater discriminative
validity than evaluation of muscle strength low back
pain12–14 and could be a very good predictor of back
health.15,16 Some electromyographic studies indicate
that the paraspinal muscles in patients with low back
pain have a faster fatigue rate compared with those in
asymptomatic subjects.9,17–19 Moreover, some investigators have focused on the endurance of the trunk
flexors in low back pain because of their significant
role in normal function of the lumbo-pelvic area.
It has also been reported that abdominal muscular
endurance in patients with low back pain is less than
that in the normal health population20–24 and apparent
loss of muscle control following trunk muscle fatigue
could be considered to be one of the important causes
of low back pain.25 Thus testing trunk muscle
endurance would seem to be very important in the prediction, prevention and rehabilitation of low back pain.
Several types of testing methods, such as static
endurance test, active measures of endurance, isokinetic and electromyographic testing, have been studied in
the literature.22 Of the different available assessment
strategies, isometric endurance testing seems to be
cost-effective, easy and quick to perform and requires
no special equipment in the clinics, so clinicians would
choose it to use for measuring trunk muscle
endurance.26 Different static endurance testing methods and evidence regarding their utilization have been
reported in the literature. Most commonly, they are:
prone isometric chest raise test as described by Ito
et al.,20 McIntosh et al.27 and others,22,23,26,28–31 prone
double straight-leg raise test as described by McIntosh
et al.27 and Moreau et al.,26 supine isometric chest raise
test as described by Ito et al.,20 Moffroid21 and
McIntosh et al.,27 supine double straight-leg raise test
as described by McIntosh et al.27 and Sorensen
test.12,26,28,32,33 The diagnostic accuracy and suitability
of a clinical test can be measured by comparing the test
results to the true condition of the patient. The most
widely used measurements used to evaluate the accuracy and suitability of clinical tests in binary data are sensitivity and specificity and predictive values of the test.
Several studies have shown a significant difference
641
between normal subjects and those with low back pain
in these tests, but more in-depth review of the literature
reveals that most previous studies have considered only
one of these tests in a relatively small population and
although there are several measures of endurance of
trunk muscle, they have not been compared. The current study collectively examined five clinical isometric
trunk muscle endurance tests in subjects with and without low back pain in a relatively large population and
identified the sensitivity, specificity, predictive values
of each test to effectively describe how well low back
pain and no-low back pain people can be classified on
the basis of their clinical endurance test values.
Methods
Subjects
Two hundred subjects between the ages of 20 and
65 were selected from four hospitals.
All the individuals who were participated in the study
filled out a simple health questionnaire. Those who met
the selection criteria were included in the study. All the
subjects signed an informed consent form approved by
the human subjects committee at the University of
Social Welfare and Rehabilitation Sciences before participating in the study. Subjects were categorized into
four groups of men and women with and without low
back pain: men without low back pain (N ⫽50, mean
(SD) age 38 (12) years), women without low back pain
(N ⫽50, mean (SD) age 43(11) years), men with low
back pain (N ⫽50, mean (SD) age 39 (12) years), and
women with low back pain (N ⫽50, mean (SD) age 43
(12) years). The mean age, height and weight of the subjects in each group are shown in Table 1.
Selection criteria
Subjects were included if they had no history of
spinal surgery, no spinal or pelvic fracture, no history of hospitalization for severe trauma or injuries
from a car accident, no history of osteoarthritis or
fracture of the lower extremities and had no history
of any systemic disease, such as arthritis or tuberculosis. Control subjects were evaluated and found
to have no complaint of any pain or dysfunction
in their low back, thoracic and neck area, lower
extremities and any neuromuscular disorders.
Patients were included if they had a history of low
642
AM Arab et al.
Table 1 Descriptive statistics for the age, height, weight and the clinical endurance tests scores in subjects with and without low back pain
Variables
Age (years)
Height (cm)
Weight (kg)
Sorensen test (s)
Prone isometric
chest raise test (s)
Supine isometric
chest raise test (s)
Prone double
straight-leg raise test (s)
Supine double
straight-leg raise test (s)
Men
Women
Without LBP (N550)
With LBP (N550)
Without LBP (N550)
With LBP (N550)
38 (12)
170 (6)
70 (12)
35 (7)
39 (12)
172 (7)
69 (11)
27 (8)
43 (11)
166 (7)
68 (13)
36 (7)
43 (12)
160 (6)
67 (10)
25 (6)
40 (9)
33 (15)
52 (18)
30 (7)
43 (9)
33 (5)
32 (5)
28 (6)
38 (6)
26 (4)
35 (5)
26 (3)
28 (4)
24 (5)
28 (4)
23 (3)
Values are mean (SD).
LBP, low back pain.
back pain for more than six weeks before the study
or had on and off back pain and had experienced at
least three episodes of low back pain, each lasting
more than one week, during the year before the
study.15 None of the patients or control subjects had
referred leg pain.
●
Reliability assessment
Using 30 asymptomatic subjects (15 male and 15
female volunteers), we assessed intratester and
intertester reliability of the measurements. The first
examiner completed the tests in a subject and then
after 15 minutes repeated the tests in a random order
on the same subject. The second examiner then tested
the subject, following the same procedure.
●
Procedures
The description of the measurement procedure for
each test was as follows:
●
Sorensen test: This is the most widely used test in
published studies evaluating the isometric
endurance of trunk extensor muscles. During the
test, the patient was on the examining table in the
prone position with the upper edge of the iliac crests
aligned with the edge of the table. The lower body
was fixed to the table by three straps, located around
the pelvis, knees and ankles. With the arms folded
across the chest, the patient was asked to maintain
the unsupported upper body in horizontal position
until he or she could no longer control the posture or
had no more tolerance for the procedure.12,26,28,32,33
Prone isometric chest raise test: This was done
with the subject lying prone on a treatment table
with a pad under the abdomen and the arms
along the sides. The subject was instructed to lift
upper trunk about 30 degrees from the table
while flexing the neck and to hold the sternum
off the floor as much as possible. The test consisted in holding this position as long as possible
while breathing normally. The detailed procedure for this test is described by Ito et al.20 and
others.22,23,26,27
Prone double straight-leg raise test: The subject’s
position was prone with hips extended, the hands
underneath the forehead and the arms perpendicular to the body. The subject was then instructed to
raise both legs until knee clearance was achieved.
The examiner monitored knee clearance by sliding
one hand under the thighs. The time was recorded
in seconds, and the test was terminated when the
subject was no longer able to maintain knee clearance. The detailed procedure for this test is
described by McIntosh et al.26,27
Clinical trunk muscle endurance tests
●
●
Supine isometric chest raise test: This was done
with the subject lying supine on a treatment table
with the hands crossed on his or her chest. The
knees and hips were in 90 degree flexion. The subject was instructed to lift neck and upper trunk
from the table and hold this position as long as
possible.26,27
Supine double straight-leg raise test: To do this
test we followed the method described by
McIntosh et al.27 to assess the endurance of the
lower abdominal muscles. The subject began in
the supine-lying position, hips extended, with the
hands laying beside the trunk. The subject was
then instructed to raise both legs from the floor
about 20 degrees and hold this position as long as
possible without any tilting in the pelvis. The
examiner monitored pelvic tilt during test. The
time was recorded in seconds and the test was terminated when the subject was no longer able to
maintain knee clearance.
The examiner undertook the clinical tests in random order and not in specified subjects.
The research was reviewed and was approved by
the Human Subject Committee at University of Social
Welfare and Rehabilitation Sciences.
Data analysis
The intraclass correlation coefficient (ICC), twoway random effect model was used to assess intratester and intertester reliability of the measurement as
described by Shrout and Fleiss.34 The receiver operating characteristic (ROC) curve analysis35 in
MedCalc statistical software (MedCalc, Mariakerke,
Belgium) was used to determine a cut-off value for
each test and the sensitivity, specificity, predictive
value and area under the curve of tests was calculated. The ROC curve is a plot of sensitivity versus
1–specificity of a variable assessed against an external criterion.35 Equivalently, the ROC curve is the
representation of the trade-offs between sensitivity
and specificity. Having or not having low back pain
was used as the external criterion for constructing
the ROC curves in this study. MedCalc statistical
software provides a value of the independent variable with the highest sensitivity and specificity as a
cut-off score which best can discriminate between
subjects with and without the condition using the
tested variable as a diagnostic tool. Separate cut-off
643
Table 2 Intraclass correlation coefficient values for intratester and intertester reliability for the measurements performed in the study (N ⫽30 subjects)
Measurements
Tester 1
ICC(3,1)
Tester 2
ICC(3,1)
Intertester
ICC(2,1)
Sorensen test
Prone isometric
chest raise test
Supine isometric
chest raise test
Prone double s
traight-leg raise
test
Supine double
straight-leg
raise test
0.80
0.90
0.79
0.89
0.78
0.90
0.92
0.90
0.89
0.87
0.85
0.83
0.84
0.85
0.79
ICC, intraclass correlation coefficient.
values and ROC curve were obtained for men and
women.
Results
Descriptive statistics for the subjects and test scores in
each group are presented in Table 1. Table 2 presents
the ICC for each test taken in the pilot study. Except
for the Sorensen test, all other ICC values were
greater than 0.80 (Table 2).
The cut-off value, sensitivity, specificity, positive
predictive values, negative predictive value and area
under the ROC curve for the tests in men and women
are presented in Table 3. The result of ROC curve
revealed that in separate analyses of data for men and
women, although all tests had somewhat good sensitivity and specificity in low back pain, among them,
the prone double straight-leg raise test had the highest sensitivity, specificity and predictive value (Table
3, Figures 1 and 2). It also had the highest area under
the ROC curve in comparison with other tests both in
men and women. Other tests had high sensitivity with
relatively low specificity or vice versa (Table 3).
Discussion
Our data indicate a relatively good sensitivity and
specificity and predictive value in all performed tests
644 AM Arab et al.
Table 3
The cut-off score, sensitivity, specificity, predictive value and area under the ROC curve for the performed tests
Tests
Cut-off score
Sorensen test
Men
Women
Prone isometric chest raise test
Men
Women
Supine isometric chest raise test
Men
Women
Prone double straight-leg raise test
Men
Women
Supine double straight-leg raise test
Men
Women
Sen.
⫹PV
Spec.
⫺PV
Area
⬎28
⬎29
92.3
84.3
76.0
84.6
80.8
84.3
90.0
84.6
0.85
0.90
⬎31
⬎33
80.8
98.0
80.0
84.6
80.08
86.2
80.0
97.8
0.79
0.93
⬎34
⬎24
96.2
99.4
72.0
32.7
78.1
59.3
94.7
99.4
0.88
0.63
⬎30
⬎29
96.2
100
100
92.3
100
92.7
96.2
100
0.99
0.97
⬎25
⬎25
92.3
98.0
80.0
84.6
82.8
86.2
90.9
97.8
0.83
0.95
Sen., sensitivity; Spec., specificity; ⫹PV, positive predictive value; ⫺PV, negative predictive value; Area, area under the ROC
curve (maximum ⫽1.0).
Equal number of men (100) and women (100) were used for all conditions.
80
80
Soren
SICR
SDSLR
PICR
PDSLR
60
40
20
Sensitivity
100
Sensitivity
100
Soren
SICR
SDSLR
PICR
PDSLR
60
40
20
0
0
0
20
40
60
80
100
100-Specificity
0
20
40
60
80
100
100-Specificity
Figure 1 ROC curve for the performed tests in men. Soren,
Sorensen test; SICR, supine isometric chest raise test;
SDSLR, supine double straight-leg raise test; PICR, prone
isometric chest raise test; PDSLR, prone double straight-leg
raise test.
Figure 2 ROC curve for the performed tests in women.
Soren, Sorensen test; SICR, supine isometric chest raise
test; SDSLR, supine double straight-leg raise test; PICR,
prone isometric chest raise test; PDSLR, prone double
straight-leg raise test.
in low back pain. This finding is in accordance with
other studies showing a significant decrease in trunk
muscle endurance in patients with chronic low back
pain.7–12,20–24 Because these muscles are rich in larger
diameter type I muscle fibres,36 they are suited to
support low levels of activity for long periods of
time. Investigators have attributed the decreased
muscle endurance found in patients with low back
pain to higher muscle metabolite level resulting from
prolonged muscle tension and spasm, muscle deconditioning and inhibition of the paraspinal muscles37,38
in response to pain and decreased activity.
However, the significance of this study was in
assessing several clinical isometric tests that have
been used to measure trunk muscle endurance together to compare the relative significance of each test
Clinical trunk muscle endurance tests
and to identify which test has the best sensitivity and
specificity in the assessment of low back pain. Our
data indicate that among all clinical tests used to
assess the endurance of trunk muscles, the prone
double straight-leg raise test has the highest sensitivity, specificity and predictive value in low back pain
compared with others both in men and women (Table
3, Figures 1 and 2). McIntosh et al.27 state that this
test assesses the lower back extensor muscles, while
others, such as the prone isometric chest raise,
Sorensen test and supine isometric chest raise, assess
upper back extensor and flexor endurance. Perhaps
the higher association of the prone double straightleg raise test with low back pain found in our study is
due to the fact that inhibition and atrophy of the
lower paraspinal muscles,38 especially the lumbar
multifidus muscles, is very important in causing low
back pain, as a result of deconditioning, impaired
muscle coordination and unequal force distribution in
these muscles.39
Hides et al.40 showed a 31% decreased crosssectional area in the lumbar multifidus muscles in
patients with low back pain, which did not resolve
automatically after remission of painful symptoms.
Although the Sorensen test is the method frequently investigated and reported in the literature, its sensitivity and specificity was lower than that of some
other tests. Published studies revealed that this test
assesses the endurance of all the muscles involved in
trunk extension, including not only the paraspinal
muscles, but also the hip extensor muscles.
Controversy exists as to the amount of endurance that
is provided by the lower lumbar extensors in contrast
with the hip extensor (gluteus maximus and hamstring).41,42 Some stated that these muscles played a
minor role,43 whereas others reported a correlation
between the position-holding time and the timecourse of hip extensor fatigability as assessed by surface electromyography, suggesting a significant role
for the hip extensor muscles. They conclude that the
Sorensen test fatigues the biceps femoris more than
the lower erector spinae and that it indicates more
about the endurance of the hip extensors than that of
trunk extensors.
Another issue that could be considered in clinical
use of the Sorensen test procedure is its difficulty.
Previous studies reported subjects have difficulty during the Sorensen test. In Biering-Sorensen’s study,
24% of the sample could not complete the test, primarily due to back pain followed by pain in the legs
645
Clinical messages
●
●
●
The prone double straight-leg raise test has
more sensitivity, specificity and predictive
value in low back pain than other tests used
in this study.
All five clinical endurance tests used in this
study showed a relatively good sensitivity
and specificity and predictive value in low
back pain.
The prone double straight-leg raise test could
be used to as a useful clinical method for testing the spinal muscle endurance in clinics.
or abdomen.24 Latikka et al. also reported a 50% failure rate in doing Sorensen test.44
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