Clinical Assessment of Trunk Flexor Muscle Strength in Healthy Girls ...

Clinical Assessment of Trunk Flexor Muscle Strength
in Healthy Girls 3 to 7 Years of Age
Karen L Baldauf, Diane K Swenson, John M Medeiros
and Sandra A Radtka
PHYS THER. 1984; 64:1203-1208.
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Clinical Assessment of Trunk Flexor Muscle
Strength in Healthy Girls 3 to 7 Years of Age
KAREN L. BALDAUF,
DIANE K. SWENSON,
JOHN M. MEDEIROS,
and SANDRA A. RADTKA
We developed a clinical method for assessing trunk flexor muscle strength in
healthy children that can be applied to assist physical therapists in determining
strength accurately in pediatric patients. In this study, we assessed trunk flexor
muscle strength in 75 healthy girls 3 to 7 years of age. Muscle strength was
graded on a scale of 0 to 5 using modified, manual muscle testing methods.
These methods attempted to minimize the amount of hip flexor muscle activity
during trunk flexion and allow more isolated action of the abdominal trunk flexor
muscles. The frequency of Normal (Grade 5) strength first appeared to predominate
at age 5 years with the majority of children demonstrating Normal (Grade 5)
strength by age 7 years. Regression analysis illustrated a positive linear relationship
(β = .37, p < .001) between mean muscle grade and age group. We discuss
muscle cross-sectional area, muscle-fiber diameter, muscle-cell number, maturation
of the central nervous system, and changes in body proportions with age
as possible contributing factors to the results of this study.
Key Words: Abdomen, Child development, Muscles, Physical therapy.
Current clinical methods of assessing muscular strength in
children are not standardized and are often highly subjective.
The physical therapist measuring strength in children may do
so by observing functional activities such as reaching, rolling,
or coming to stance. The child may be asked to perform a
specific movement or to maintain a position to test the
strength of specific muscle groups. Grades for adult manual
muscle tests are often used as the norm when testing trunk
flexor muscle strength in children. This study presents a
clinically feasible method for assessing trunk flexor muscle
strength in children by using testing procedures appropriate
to a child's level of ability.
Various manual muscle testing methods have been used to
assess adult abdominal strength clinically. Kendall et al have
proposed two different procedures to measure abdominal
muscle strength. 1 One method assesses a person's ability to
keep the lumbar spine flat against the table while lowering
both legs, with knees extended, from an initial position of 90
degrees of hip flexion. The point in the range of motion at
which the lumbar spine begins to demonstrate lordosis determines
the muscle grade. Their second method assesses
strength based on the ability to flex the vertebral column and
come to a sitting position while the legs remain stabilized in
Ms. Baldauf and Ms. Swenson were Master of Arts candidates when this
research was completed at the Division of Physical Therapy, Stanford University
School of Medicine, Stanford, CA 94305.
Ms. Baldauf is now Staff Physical Therapist, Veteran's Administration
Hospital, Palo Alto, CA 94304 (USA).
Ms. Swenson is now a physical therapist at California Children's Services,
Alameda County, CA 94607.
Dr. Medeiros is Acting Director and Assistant Professor, Division of Physical
Therapy, Stanford University School of Medicine, Stanford, CA 94305.
Ms. Radtka is a doctoral candidate, School of Education, University of
California, Berkeley, CA 94720.
This article was submitted June 27, 1983; was with the authors for revision
22 weeks; and was accepted March 1,1984.
extension. Daniels and Worthingham assign grades of trunk
flexor muscle strength by having the person clear the scapulae
from the table during trunk flexion. 2 The lower extremities
are stabilized in extension during their Normal (Grade 5),
Good (Grade 4), and Fair (Grade 3) muscle test positions.
Harvey and Scott attempted to measure abdominal muscle
strength in young women using a timed curl-up (reverse situp)
test. 3 Adult abdominal muscle strength has been quantitatively
measured in the supine position using a
dynamometer 4 and the Cybex ® II* isokinetic dynamometer
system. 5 Adult trunk flexor muscle strength has similarly been
assessed using the Cybex ® II dynamometer. 6.7 A protocol has
recently been developed for testing trunk flexor strength in
the upright position using the Cybex ® II system. 8
Numerous electromyographic (EMG) studies have attempted
to determine the positions in which the abdominal
muscles are the most active. Such information is useful in
maximizing abdominal muscle activity during strength testing.
Flint has established that rectus abdominus muscle activity
is greatest in the early stages of trunk flexion and decreases
as the iliacus muscle becomes more active when the trunk is
flexed past 45 degrees. 9,10 Halpern and Bleck compared the
duration of abdominal muscle activity in various sit-up positions.
11 They found initial trunk flexion through partial range
(scapular clearance) elicited the greatest duration of abdominal
muscle activity. The position of hip and knee flexion has
been shown to increase the amount of EMG activity from the
rectus abdominus muscle 12, l3 (pp30l-309) and to decrease the activity
of the rectus femoris muscles. 14 Eliminating stabilization
to the lower extremities during trunk flexion has also been
shown to increase the activity of the rectus abdominus
* Cybex, Div of Lumex, Inc, 2100 Smithtown Ave, Ronkonkoma, NY
11779.
Volume 64 / Number 8, August 1984 1203
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muscle 10 and to decrease rectus femoris muscle activity. 12,14,l5
The decrease in activity of the hip flexor muscles during situps
with hip and knee flexion and without stabilization is
generally attributed to the shortened position of these muscles.
13 (pp301-309), 15 Girardin states, "The reduction in distance
between the origin and insertion of the hip flexors and
the psoas has most probably decreased their participation and
therefore enhanced the rectus abdominus involvement. " 13(p307)
Measures of normal strength in children have focused
largely on physical fitness tests. The American Association
for Health, Physical Education, and Recreation in 1956 assessed
abdominal muscle strength in children by having them
flex and rotate the trunk while the lower extremities were
supported in an extended position. 16 Children throughout the
United States were assigned percentile grades (as measures of
abdominal strength) according to the maximum number of
sit-ups they could complete. The revised 1975 version of the
sit-up test measured the number of sit-ups a child could
perform in one minute. 17 In this procedure, the hips and
knees were flexed, feet were supported, and the trunk rotation
requirement was eliminated. Percentile normative data for
these tests were computed throughout the United States for
500 children who were 7 through 15 years of age. Glover,
using the same sit-up procedure with a 30-second time limit,
established norms of abdominal muscle strength for primary
grade children. 18 Flint and Diehl attempted to quantify abdominal
strength in children using a cable tensiometer to
measure the force of trunk flexion. 19 Sit-ups with knees flexed
and feet stabilized were performed for this measurement.
Sit-ups performed through full range of trunk flexion may
cause or contribute to degenerative changes in the lumbar
disks. 8 The stress placed on the lumbar spine is decreased with
trunk flexion through partial range of motion. 20 Therefore,
sit-ups performed through partial range may be an effective
method of measuring abdominal muscle strength while protecting
the lumbar spine.
A position that maximizes the action of the abdominal
muscles during trunk flexion must be developed to assess
abdominal muscle function. Electromyographic research and
biomechanical principles have provided the basis for modifying
current trunk flexor muscle test positions. The purpose
of this study is to assess clinically trunk flexor muscle strength
in girls 3 to 7 years of age using a method based on results of
EMG and biomechanical investigations.
METHOD
Subjects
Using a sample of convenience, we selected 80 girls 3 to 7
years of age to participate in this study. All subjects were
healthy girls residing in the San Francisco Bay area who met
the following inclusion criteria: 1) no history of hip or trunk
surgery reported by parents and 2) ability to perform neck
flexion in the supine position through full range of motion.
Two subjects were excluded because of past surgeries. Two 3year-old
subjects and one 4-year-old subject were excluded
because of their inability to perform neck flexion through full
range of motion against gravity. The remaining 75 children
were divided into five groups according to exact chronological
age in years with 15 girls in each age group. The researchers
recorded height, weight, and birthdate for each child. We
obtained parental consent forms for each subject before the
subjects participated in this study.
Equipment
We constructed an adjustable thigh stabilization board to
support each child's hips in 90 degrees of flexion during the
test procedure. The lower legs rested over the top of the board
in approximately 120 degrees of knee flexion. We supplied
the subjects with a floor exercise mat for comfort.
Test Design and Grading
We placed the subjects in a supine position on the mat in
a modified sit-up position with hips flexed to 90 degrees and
knees flexed approximately 120 degrees across the top of the
board. We chose this position to maximize the activity of the
abdominal trunk flexor muscles and minimize the activity of
the hip flexor muscles.
We assigned numerical values.to muscle grades (Normal,
Grade 5; Good, Grade 4; Fair, Grade 3; Poor, Grade 2; Trace,
Grade 1; and Zero, Grade 0). The vertebral spinous process
at the level of the inferior angle of the scapulae was marked
with an adhesive circle, 0.5 in (1.27 cm) in diameter. The
criterion for passing the muscle test in the Normal, Good,
and Fair positions was the subject's ability to lift the marked
vertebra completely from the mat so that the vertebra was
visible to one examiner seated on the floor about 2 ft (0.61
m) behind the child. We adapted upper extremity positions
for each muscle test from the trunk flexor muscle testing
method of Daniels and Worthingham. 2 For a Normal muscle
test grade, the child's hands were clasped behind the neck and
arms were adducted over the ears during trunk flexion (Fig.
1). In the Good muscle test position, arms were folded across
the chest (Fig. 2). Arms were extended with approximately 90
degrees of shoulder flexion in the Fair muscle test position
(Fig. 3). A Poor muscle test grade was assigned if the subject
could not pass the Fair muscle test but could flex the cervical
spine and partially lift the scapulae from the mat (Fig. 4). A
Trace muscle test grade was assigned if the subject could not
pass the Poor muscle test but could contract the abdominal
muscles during coughing, exhaling, or attempting to flex the
Fig. 1. Normal (Grade 5) muscle test position.
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Fig. 2. Good (Grade 4) muscle test position.
trunk, as determined by palpation. 2 A Zero muscle test grade
was given to a subject if no abdominal muscle activity could
be palpated. Each subject was allowed a maximum of three
trials to complete the test for each muscle grade. We assigned
a muscle test grade after the first successful trial of each
muscle test.
Muscle tests were administered and graded for each child
by the researchers. We conducted a pilot study (N = 7) that
established interrater reliability at 100 percent.
Procedure
Each child removed her shirt. The child stood in relaxed
stance with her arms at her sides while we centered the
reference marker over the designated spinous process. We
positioned each child in supine on the mat with the hips
flexed to 90 degrees and the knees placed across the board in
approximately 120 degrees of flexion. We assessed each child's
ability to perform neck flexion through full range of motion
in the supine position because this movement is used for the
initiation of trunk flexion. Then one researcher demonstrated
to each subject the Fair trunk flexor muscle test procedure.
The child was allowed to practice the movement once. Each
child had three trials in which to complete the test successfully
in the Fair muscle test position. We gave a 30-second rest
period between all trials. After the first successfully completed
trial in the Fair test position, we demonstrated the Good
muscle test to the child and allowed one practice trial. If the
subject could complete the Good muscle test in one of the
three trials, we demonstrated the Normal muscle test procedure
for the subject to practice and attempt. If the child could
not pass the Fair muscle test, we tested the child according to
the Poor, Trace, and Zero test procedures and assigned a
grade according to level of test achievement.
Data Analysis
We assigned numerical values (0-5) to the muscle grades
for statistical analysis. We believed the assignment of numerical
values to ordinal data was appropriate for the statistical
analysis of this study because 1) numerical values allowed the
use of more flexible and powerful parametric tests and 2) the
RESEARCH
assignment of any numerical scale to such data seldom produces
marked differences in the conclusions drawn from the
analysis. 21
We performed a Pearson product-moment correlation to
determine the relationship of the variables height, weight, and
age to muscle grade, and a one-way analysis of variance
(ANOVA) to determine if significant differences existed
among the mean muscle grades of each age group. We also
performed a stepwise multiple regression analysis for the same
variables.
RESULTS
Table 1 records means and standard deviations for muscle
grade, age (in months), height, and weight by age group (in
years). As shown in Table 1, the mean muscle grade of 3- and
4-year-old subjects was in the Fair range (3.3 and 3.7) and
that of 5- and 6-year-old subjects was in the Good range (4.1
and 4.4). Seven-year-old girls had a mean muscle grade close
to Normal (4.8) strength.
Fig. 3. Fair (Grade 3) muscle test position.
Fig. 4. Poor (Grade 2) muscle test position.
Volume 64 / Number 8, August 1984 1205
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TABLE 1
Means and Standard Deviations of Variables by Age Group
Variable
Age
(mo)
Height
(in)
Weight
(lb)
Muscle
grade
3
(n = 15)
s
41.1 3.4
39.2 1.4
32.6 3.5
3.3 1.0
4
(n = 15)
s
54.5 2.5
42.9 1.7
37.5 4.3
3.7 1.1
Age Group (yr)
5
(n = 15)
s
65.3 3.1
45.0 2.2
42.1 5.9
4.1 1.2
6
(n = 15)
s
77.7 3.4
47.2 1.7
47.0 3.7
4.4 0.9
7
(n = 15)
s
89.1 2.7
49.9 1.3
53.8 5.7
4.8 0.6
TABLE 2
Pearson Product-Moment Correlations for Age, Height, Weight,
and Muscle Grade
Variable
Age with height
Age with weight
Height with weight
Age with muscle grade
Weight with muscle grade
Height with muscle grade
a p

Fig. 5. Frequency of muscle grades by age group.
against gravity, the trunk flexor muscle test may be more
difficult for the younger age groups.
We excluded from this study children who did not have
full neck flexion strength against gravity. Therefore, the reported
values of trunk flexor muscle grades may be higher
than those of many children, especially the younger age
groups.
The assignment of a criterion-based muscle grade did not
account for the quality of movement. Although the younger
children often completed the requirements for a specific muscle
grade, they did not exhibit the same quality of movement
as older children who received the same muscle grade. We
observed that, in general, younger children took more time
to complete the tests, attempted to use more trunk rotation
instead of pure trunk flexion, and lacked the smoothness of
movement that was present in the older children.
Further study needs to be conducted on a larger, randomly
selected group of both sexes to establish normative trunk
flexor muscle grades in children. Such research should include
testing a wider age range including older children and adolescents.
Muscle strength testing in children under 3 years of age
may not be feasible because of their inability to follow instructions.
Measure of isometric trunk flexor muscle strength,
including duration of contraction, may also be useful in
assessing trunk flexor muscle strength in children. In addition,
simultaneous EMG recordings from the abdominal and hip
flexor muscles would be useful in determining the relative Fig. 6. Regression line for muscle grade vs subject age.
RESEARCH
Volume 64 / Number 8, August 1984 1207
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contribution of these muscles during trunk flexion muscle
testing procedures.
Clinical Implications
The results of this study have clinical significance to physical
therapists assessing and treating pediatric patients. This
method of measuring trunk flexor muscle strength can be
easily adapted to clinical practice. The suggested values of
trunk flexor muscle strength serve as guidelines of assessing
performance in these specific age groups. In addition, the
suggested increase in muscle grade for each year of age may
be used to measure incremental strength gains in a developing
child.
CONCLUSION
We developed a clinical method for assessing trunk flexor
muscle strength using principles of EMG and biomechanics.
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Trunk flexor muscle strength in girls between the ages of 3
and 7 years increased proportionately with age by approximately
one-third of a muscle grade a year. The mean muscle
grade for the 3- to 7-year-old age groups was 3.3, 3.7, 4.1, 4.4,
and 4.8, respectively. Factors suggested as having a possible
influence on the development of trunk flexor muscle strength
included muscle cross-sectional area, muscle-fiber diameter,
muscle-cell number, maturation of the CNS, and changes in
body proportions with age. The reported values of trunk flexor
muscle grades serve as guidelines for assessment of trunk
flexor muscle strength in pediatric patients 3 to 7 years of age.
Acknowledgments. We thank Dr. Rupert Miller, PhD, for
his statistical consultation and Valerie Coon, MA, for her
valuable consultative services. We also give thanks to Eric
Swenson for his assistance with equipment design and photography
and to Jack Baldauf for his assistance with figure
preparation.
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1208 PHYSICAL THERAPY
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Clinical Assessment of Trunk Flexor Muscle Strength
in Healthy Girls 3 to 7 Years of Age
Karen L Baldauf, Diane K Swenson, John M Medeiros
and Sandra A Radtka
PHYS THER. 1984; 64:1203-1208.
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