Journal of Strength and Conditioning Research, 2005, 19(4), 925–930
q 2005 National Strength & Conditioning Association
VALIDATION OF AN ABDOMINAL MUSCLE STRENGTH
TEST WITH DYNAMOMETRY
CARLOS E. LADEIRA,1 LARRY W. HESS,2 BENJAMIN M. GALIN,3 STEPHAN FRADERA,4
MELISSA A. HARKNESS5
AND
College of Allied Health, Health Profession Division, Physical Therapy Program, Nova Southeastern University,
Fort Lauderdale, Florida 33328; 2Washington Redskins, Ashburn, Virginia 20147; 3Therapy on Demand, Inc.,
Wellington, Florida 33414; 4Physical Therapy, O’Connor Hospital, San Jose, Califonia 95128; 5Allied Physical
Therapy, Cape Coral, Florida 33915.
1
ABSTRACT. Ladeira, C.E., L. Hess, B. Galin, S. Fradera, and M.
Giddings. Validation of an abdominal muscle strength test with
dynamometry. J. Strength Cond. Res. 19(4):925–930. 2005.—Adequate abdominal strength prevents work- and sports-related injuries and stabilizes the spine for athletic activities. The doubleleg-lowering maneuver (DLLM) is a popular test to assess abdominal strength because of its simplicity; however, its validity
and reliability have not been studied thoroughly. To determine
the validity and reliability of the DLLM, 4 examiners evaluated
28 subjects. The validity of the DLLM was evaluated with the
Nicholas Hand-Held Dynamometer (NHHD) as the gold standard. The DLLM scores were compared to themselves for reliability and to NHHD scores for validity. Reliability for the
DLLM was very high (r 5 0.932). Validity of the DLLM was low
(r 5 20.338 to 20.446). The DLLM is reliable, but it has low
validity to assess abdominal strength. The DLLM may be a useful tool to assess pelvic tilt motor control for spine stability, but
it is not suitable for assessing muscle strength.
KEY WORDS. manual muscle test, motor control, trunk flexors,
reliability
INTRODUCTION
dequate abdominal muscle strength is important in order to prevent work- and sports-related lumbar injures, to prevent acute back
pain from becoming chronic, and to stabilize
the spine for efficient motor performance during demanding athletic activities (20, 28, 33, 34, 36). Good
abdominal strength may reduce lumbar disc pressure,
preventing degenerative disc disease. Abdominal muscle
contraction is also crucial for stabilizing the spine, which
prevents tears of the soft tissues of the lumbar area and
allows fast, coordinated extremity movements in sports
(10). For all of the above reasons, abdominal muscle
strength testing is vital in physical therapy and athletic
training practice. The double-leg-lowering maneuver
(DLLM) is a popular manual muscle test (MMT) to assess
abdominal muscle strength because of its simplicity and
low cost. DLLM is described in MMT textbooks used in
physical therapy, physical education, and athletic training education (6, 18).
MMT procedures were designed to diagnose weakness
in patients with neurological and orthopedic disorders
and diseases (12, 16, 17, 23, 37); they were not originally
designed to measure muscle strength in healthy adults.
The validity of MMT procedures in identifying strength
deficits in healthy adults and in athletes with sports injuries is questionable 1, 3–5, 9). Despite lack of validation,
the DLLM is used in physical therapy, physical educa-
A
tion, and athletic training practice to evaluate the
strength of the abdominal muscles. We investigated the
validity of the DLLM as a test of abdominal muscle
strength.
The DLLM has not been validated with dynamometry;
its validity has been studied with electromyography
(EMG). EMG studies have shown that the DLLM places
a great demand on the abdominal muscles (11, 28, 30, 33);
however, this does not show that this maneuver is valid
to assess muscle strength. EMG studies record muscle activity during body movements; they do not record the ability of a muscle to produce force. Muscle activity is not
directly related to the production of muscle force. Someone may exercise with less muscle activity but produce
more muscle force. Higher muscle force with less muscle
activity may mean that a muscle group requires less fiber
recruitment or less muscle firing to produce force (11, 28,
30, 33). Therefore, because EMG assesses only muscle activity during the DLLM procedure, the DLLM needs to
be validated with an instrument that records force (a dynamometer).
We studied the validity of the DLLM with the Nicholas Hand-Held Dynamometer (NHHD; Lafayette Instrument Co., Lafayette, IN) as a gold standard to validate
the DLLM because of its recognized validity and reliability (20, 35, 36). In addition, because the reliability of the
DLLM has not been thoroughly determined, we also investigated its reliability. To summarize, the purpose of
the study was twofold: Part A was designed to determine
the intrarater reliability of the DLLM, and Part B to determine the construct validity of the DLLM.
METHODS
Experimental Approach to the Problem
This was a quantitative, nonexperimental, correlational
study. As stated previously, the NHHD served as the gold
standard for determining the construct validity of the
DLLM. We used the NHHD because it has been shown
to be very sensitive in detecting muscle force differences
even for athletes without muscle impairments. The
NHHD is comparable to sophisticated isokinetic devices
when measuring muscle force isometrically; it has been
shown to be reliable and valid (20, 35). The dynamometer
used in our study allowed us to verify whether the DLLM
may detect small muscle impairments.
We used a modified method more sensitive than that
used traditionally to score muscle strength with the
DLLM. Kendall et al. (18) and Cutter and Kevorkian (6)
925
926
LADEIRA, HESS, GALIN
ET AL.
TABLE 1. Manual muscle grading system for the double-leglowering maneuver.*
Hip angle Muscle Numerical Hip/angle
(8) (6)
grade
grade
(8) (18)
90
75
60
45
30
15
0
Poor
Fair
Fair1
Good2
Good
Good1
Normal
2
3
31
42
4
41
5
75–90
60–75
45–60
30–45
15–30
0–15
NA
Muscle Numerical
grade
grade
Fair
Fair1
Good2
Good
Good1
Normal
NA
5
6
7
8
9
10
NA
* Grading systems for the double-leg lowering test adapted
from Cutter & Kevorkian (6) and from Kendall et al. (18).
used ordinal data with 6 or 7 scores based on hip range
of motion degree increments ranging from 158 to 308 during the DLLM (Table 1). In our method, we did not use a
scale with ordinal data to grade muscle strength, as is
traditionally advocated. We used ratio data in terms of
degrees of hip range of motion during the DLLM with a
scale of 08 to 908 and increments of 18. It is important to
note that a higher score in the NHHD represents higher
muscle performance and a higher score on the DLLM
means lower muscle performance; for this reason, we expected that the correlation between the DLLM and
NHHD, if any, would be negative. The interpretation of
our results was based on correlation coefficient standards
recommended by Munro (26) for health sciences: 0.00 to
0.25, little; 0.25 to 0.49, low; 0.50 to 0.69, moderate; 0.70
to 0.89, high; and 0.90 to 1.00, very high.
The subjects were all tested in 1 day. Four student
physical therapists under the supervision of a licensed
physical therapist collected the data. Two testers (1 and
2) collected data with the NHHD, and 2 other testers (3
and 4) collected the DLLM data. Two trials (A and B)
were performed for each procedure (NHHD and DLLM).
Each trial consisted of 3 repetitions. The subjects had a
break of 30 seconds between each repetition. The average
of the 3 repetitions was the final score for the trial. First,
the subjects performed the 3 repetitions for the NHHD
(NHHD-A) with a 1-minute rest before completing the 3
repetitions for the DLLM (DLLM-A). After 15 minutes, a
second trial (NHHD-B and DLLM-B) was completed in
the exact order and rest interval as for trial A. All testers
performed the same duties throughout the study.
Subjects
The subjects were 28 volunteers (16 men and 12 women)
between the ages of 21 and 40. Subjects signed a consent
form prior to participating in the study. The participants
were healthy individuals, free from musculoskeletal, neurological, and cardiopulmonary conditions. The Institutional Research Board at Nova Southeastern University
approved the research protocol.
Procedures
The NHHD testing procedure is shown in Figure 1. A
stabilizing system was constructed to maximize the validity and reliability of the NHHD (5, 27). Tester 1 recorded
the data while Tester 2 provided verbal instructions and
encouragement. The subjects were positioned supine under a stabilizing bar that held the NHHD for the measurement. The dynamometer was positioned over a
marked point that was 2 inches superior to the base of
FIGURE 1. Subject positioning for abdominal strength testing
with the Nicolas Hand Held Dynamometer. (A) Location of
placement for dynamometer over xyphoid process. From this
positioning, the subjects would flex the trunk and press the
chest against the stabilized dynamometer.
the xyphoid process. The subject’s hips and knees were
positioned at 908 with an adjustable bench to minimize
the activity of the hip flexors and maximize the activity
of the abdominals (11, 28, 30). The bar was adjusted to
allow approximately 158 to 308 of trunk flexion and to
allow subjects to raise their scapulas from the mat. The
previous positioning was based on studies to isolate the
action of the abdominal muscles from the hip flexors (5,
11, 27, 28, 30). Subjects were instructed to perform a submaximal test lasting 4 seconds to warm up and familiarize themselves with the testing procedures before the beginning of data collection. Subjects were verbally instructed to raise their trunks from the mat and to push
into the dynamometer force plate. With the sternum positioned against the force plate, the subjects performed a
maximal isometric contraction (Figure 1). Subjects completed 3 maximal repetitions, lasting 4 seconds each, with
30 seconds of rest between each attempt. The average of
the 3 scores was recorded as the final value for each trial.
The DLLM procedure is shown in Figure 2a,b. We
modified the DLLM procedure to improve its reliability,
accuracy, and sensitivity. In the original method, the subject to be tested lies supine on an examination table; his
or her lumbar spine is firmly pressed against this table
by isometric abdominal contraction. The hips are flexed
to 908, with the knees and ankles in neutral position.
Then, the subject lowers the extremities while maintaining the knees in neutral position and contracting the abdominal muscles to prevent anterior tilting of the pelvis.
As the subject lowers the legs, the examiner looks for the
first sign of anterior pelvic rotation through palpation
and visual observation. The examiner scores the test
based on the angle at which the pelvis first rotates or tilts
anteriorly. The scores are arbitrarily derived from normal
scales of manual muscle testing (Table 1). In our modified
method, we measured pressure of the lumbar spine
against the table with a sphygmomanometer (McCoy Co.,
Maryland Heights, MO) as suggested by Gilleard and
Brown (11). We observed the hip angle at which the subjects lost control of this pressure with a digital inclinometer (Saunders, Chaska, MN).
In our modified procedure (Figure 2a,b), Tester 3 monitored the digital inclinometer and Tester 4 monitored the
VALIDATION OF
AN
ABDOMINAL MUSCLE TEST 927
TABLE 2. Descriptive statistics for study measurement procedures.
Procedure*
DLLM trial A (8)
DLLM trial B (8)
NHHD trial A (N)
NHHD trial B (N)
Mean
SD
SE
72.9
20.45
3.87
75.5
17.41
3.28
199.1 113.15 21.24
209.2 124.25 23.44
Maximum Minimum
90
90
497.2
514.9
27
31
41.2
35.3
* DLLM 5 double-leg-lowering maneuver with values in degrees of range of hip flexion; NHHD 5 Nicholas Hand-Held Dynamometer with values representing force (N).
abdominal muscles relaxed. The subject was then instructed to contract the abdominal muscles and maintain
a posterior pelvic tilt, bringing the pressure to 40 mm Hg.
Then, while slowly lowering their legs, the subjects were
asked to maintain pelvic tilt without letting the dial drop
below 20 mm Hg. Tester 4 immediately notified Tester 3
to record the corresponding angle from the inclinometer
when the sphygmomanometer gauge dial dropped below
20 mm Hg. The setting of the pressure at 40 (initial startup point) and 20 mm Hg (cutoff point for final reading)
for the procedure was based on a previous unpublished
pilot study. In the unpublished pilot study, we noticed
that abdominal contraction causing pressure above 40
mm Hg was uncomfortable and difficult to achieve for
some subjects. We also observed that a pressure drop below 20 mm Hg was difficult to monitor because of wide
fluctuations on the sphygmomanometer dial. The idea to
use a sphygmomanometer to monitor lumbar pelvic tilt
positioning was adapted from a procedure previously
used by Gilleard and Brown (11). Subjects completed a
total of 3 repetitions with 30 seconds of rest in between.
The average of the repetitions was the final scored value
for the trial.
FIGURE 2A. Initial subject positioning for the double-leglowering maneuver. The subject lies supine with her hips
positioned at 908 of hip flexion. The pressure on the
sphygmomanometer is brought to 20 mm Hg. The subject then
contracts her abdominals with the cuff underneath the small
of her back on the level of the umbilicus to bring the pressure
to 40 mm Hg.
FIGURE 2B. The subject is asked to lower her legs
simultaneously while keeping her knees straight and doing her
best to prevent the pressure on the sphygmomanometer dial to
drop below 20 mm Hg. When the pressure drops below 20 mm
Hg, the hip angle is read from the inclinometer on her thigh.
sphygmomanometer. Subjects were positioned supine
with hips flexed at 908 and knees straight. The sphygmomanometer was aligned with the length of the spine
and centered directly beneath the umbilicus. It was further positioned between the iliac crest and the posterior
superior iliac spines. The inclinometer was attached to
the subject’s right thigh, 2 inches proximal to the superior
border of the patella (Figure 2a,b). Subjects were first instructed to perform a posterior pelvic tilt to help familiarize themselves with the correct positioning during the
actual trials. The inclinometer dial was adjusted to 08.
Tester 3 then passively raised the subject’s leg to 908 (as
measured on the inclinometer). The blood pressure cuff
was placed under the lumbar spine and the pressure in
the sphygmomanometer was set at 20 mm Hg with the
Statistical Analyses
Descriptive statistics consisting of mean, standard deviation, and range were calculated for trials A and B of both
the DLLM and the NHHD (Table 2). For Part A of the
study, we used the intraclass correlation coefficient (model 1) test (a 5 0.05) to determine the reliability of the
DLLM and the NHHD. This model is the standard correlation test for intrarater reliability; it accounts for measurement correlation and agreement (26).
For Part B, we used a Pearson correlation to determine the validity of the DLLM compared to NHHD (a 5
0.05). The Pearson test determines measurement correlation without measurement agreement. The scores from
the NHHD (muscle force in N) and DLLM (range of motion in degrees) are different; therefore, they require a
correlation test that does not assess measurement agreement. We plotted the correlation relationship in a graph
with each DLLM score compared to each NHHD score.
Then, we plotted a best-fit line to visually show the relationships between the data (Figure 3a,b). We also measured gender effect, because men have different bodyweight distribution in the lower extremities than women
(7), which could skew the performance of this test.
We calculated the power of the analyses for the reliability and the validity. We used a 5 0.05 for the calculations. For the reliability analysis, the calculation was 2tailed. However, for the validity study, the power calculation was 1-tailed because, as previously explained, we
928
LADEIRA, HESS, GALIN
ET AL.
were expecting an inverse (negative correlation) relationship between the measurements of the DLLM and the
NHHD.
RESULTS
In Part A of the study, the reliability of the DLLM was
very high (r 5 0.932) and statistically significant (Table
3). The power for the previous calculation was 99% because of the large observed effect size. Based on this result, we reject the null hypothesis of the reliability study.
This means that the DLLM is a very reliable maneuver.
The intrarater reliability of the NHHD was very high (r
5 0.968, p , 0.001), showing the high quality of our gold
standard.
In Part B of the study, the relationship between the
DLLM and the NHHD showed an inverse correlation, as
we predicted. The correlation matrix displays the validity
of the modified DLLM and NHHD (Table 4). The correlation between the NHHD and the DLLM ranged between
20.338 and 20.446 and was statistically significant (Table 4). Based on this result, we reject the null hypothesis
for the validity study. The power for these previous calculations ranged between 55.79% and 78.66%; the power
was lower for these previous calculations because of the
small observed correlation coefficients (effect size). Gender effect in the correlation was not significant; adding
gender into the model brought the overall correlation to
a nonsignificant level.
DISCUSSION
FIGURE 3A. Correlation scatter plot with best line fit
between Nicholas Hand-Held Dynamometer trial A (NHHD-A)
and double-leg-lowering maneuver trial A (DLLM-A).
FIGURE 3B. Correlation scatter plot with best line fit
between Nicholas Hand-Held Dynamometer trial B (NHHD-B)
and double-leg-lowering maneuver trial B (DLLM-B).
Our study had 2 main parts: Part A, to determine the
reliability of the DLLM, and Part B, to determine the validity of the DLLM. The first part of this discussion focused on the reliability of the DLLM. Prior studies have
questioned the reliability of the DLLM because of the inherent subjectivity of the test; more specifically, the ability of the raters to eyeball hip motion during the DLLM
and to detect pelvic tilt motion with palpation (31, 32, 38).
Zannotti et al (38) reported moderate reliability for
the DLLM; their correlation coefficient was 0.55 for the
test early (first degrees of hip motion) in the DLLM. They
deemed their reliability unacceptable based on this moderate correlation. Our DLLM procedure had very high reliability (r 5 0.932). The main reason why our results
were better than those of Zannotti et al was probably because of our different testing procedures. Zannotti et al.
measured pelvic tilt positioning with a video recording
system without instructions to subjects to maintain abdominal contraction at a determined tension level during
their procedure. We measured pelvic tilt control based on
instructions to subjects to maintain abdominal contrac-
TABLE 3. Intraclass correlation coefficient for the double-leg-lowering maneuver.
Single measures
Average measures
95% confidence interval
F test with true value 0
Intraclass
correlation
Lower bound
Upper bound
Value
df1
df2
Significance
0.914
0.955
0.825
0.904
0.959
0.979
22.365
22.365
27
27
28
28
0.000
0.000
One-way random effects model in which people effects are random.
Summary item statistics
Mean
Minimum
Maximum
Range
Maximum/
minimum
Variance
No. of items
Interitem correlations
0.932
0.932
0.932
0.000
1.000
0.000
2
The covariance matrix is calculated and used in the analysis.
VALIDATION OF
AN
ABDOMINAL MUSCLE TEST 929
TABLE 4. Pearson correlation matrix for the Nicholas Hand-Held Dynamometer (NHHD) and the double-leg-lowering maneuver
(DLLM).*
DLLM-A
DLLM-A
DLLM-B
NHHD-A
NHHD-B
Pearson
p
Pearson
p
Pearson
p
Pearson
p
1
correlation
correlation
correlation
correlation
0.932(**)
0.000
20.360(*)
0.030
20.338(*)
0.039
DLLM-B
NHHD-A
NHHD-B
0.932†
0.000
1
20.360‡
0.030
20.446†
0.009
1
20.338‡
0.039
20.438†
0.010
0.968†
0.000
1
20.446†
0.009
20.438†
0.010
0.968†
0.000
* A 5 first trial; B 5 second trial.
† Correlation is significant at the 0.01 level (1-tailed).
‡ Correlation is significant at the 0.05 level (1-tailed).
tion at similar tension levels in our procedure. We feel
that our method is a better representation of abdominal
muscle performance than that of Zannotti et al. because
our testing procedure focused on the ability of the subjects to maintain pelvic tilt positioning through a consistent guided level of abdominal muscle contraction, whereas Zannotti et al. focused their procedure on pelvic tilt
motion, disregarding how much effort the abdominal
muscles exerted to maintain pelvic tilt positioning.
The second part of our study addressed the validity of
the DLLM. There was a low correlation (r 5 20.338 to
20.446) between the NHHD and the DLLM (26). The
power for these correlations (55.79–78.66%) did not exceed the standard accepted 80% in statistical calculations.
The unsatisfactory power was related to the low observed
correlation coefficients (effect size) or to the small sample
size. If we had used a sample of 29 subjects, the power
for effect size 20.446 would have exceeded 80%; and if
we had used a sample of 53 subjects, the power for effect
size 20.338 would have exceeded 80%.
Gilleard and Brown (11) studied the validity of the
DLLM with EMG studies and did not find an increase of
the primary trunk flexors’ EMG activity during this test.
They reported that as the subjects lowered their legs during the DLLM, there was a relative decrease in the activity of the rectus abdominal muscle with a concomitant
increase in the activity of the oblique abdominal muscle.
Our results were similar to the results of Gilleard and
Brown in that we found a low correlation between the
DLLM and abdominal muscle force. In other words, the
activity of the abdominal muscles was not related to the
ability of the subjects to control their pelvic tilt while lowering their legs, and also was not related to subject’s
strength test performance. Therefore, based on our results and the results of the study published by Gilleard
and Brown, we concluded that the DLLM had poor validity to measure abdominal muscle strength.
The DLLM was originally designed to assess lower abdominal muscle strength (6, 18), whereas the NHHD assesses combined lower and upper abdominal muscle
strength (13); if the DLLM did what it was designed to
do, the value of the NHHD to validate the DLLM could
be questioned. However, the DLLM does not isolate the
lower abdominal muscles as claimed in MMT books (6,
18). EMG studies have shown that the DLLM activates
the lower and upper abdominals together, not separately
(10, 22, 27, 29, 32). Therefore, the NHHD is an appropriate gold standard to validate the DLLM.
The results of our study should not be generalized to
populations with obvious neuromuscular impairments,
because we tested healthy adult individuals with no history of neuromuscular pathology. In addition, the results
of our study did not take into consideration gravity correction for measurement of muscle strength with the
NHHD. However, because of the low correlation between
the NHHD and the DLLM (20.338 to 20.446), we believe
that gravity correction with body-weight adjustments
would not have made significant changes in the overall
results of the study.
We recommend future studies to investigate the relationship between pelvic tilt motor control and the incidence of back pain. We also recommend new investigations to examine the relationship between pelvic tilt motor control and performance in sports requiring spine stability for fine lower-extremity motor control, such as
gymnastics and trampoline diving. In addition, we suggest that new studies investigate whether pelvic tilt motor control can be trained with the new core strengthening exercise methods advocated in rehabilitation medicine for improving lumbar functional stability (2, 8, 14,
15, 25).
PRACTICAL APPLICATIONS
We do not believe that the DLLM has practical applications for measuring muscle strength as claimed in MMT
textbooks (6, 18). Therefore, we recommend that practitioners discontinue using the DLLM to measure muscle
strength. In our opinion, the DLLM is a test of pelvic tilt
motor control. We believe that the DLLM may still be a
valuable tool in physical therapy, physical education, and
athletic training practice, despite its low validity to assess
muscle strength. The DLLM has very high reliability. We
consider the DLLM a reliable maneuver to assess pelvic
tilt motor control through abdominal contraction rather
than a method to assess abdominal muscle strength. Motor control is also an important component of performance
in sports and prevention of injures (8, 14, 15, 25). The
DLLM may be important in rehabilitation medicine because it is a method to assess the pelvic tilt motor control
required to maintain lumbar functional stability.
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Acknowledgments
We thank Dr. Cheryl Hill (Professor in the Physical Therapy
Program) for proofreading and reviewing the manuscript.
Address correspondence to Carlos Emilio Ladeira,
cladeira@nova.edu.