Running head: THE RELIABILITY OF MANUAL MUSCLE TESTING THROUGH THE
COMPARISON OF THE ISOKINETIC BIODEX TESTING ABOUT THE KNEE JOINT
The Reliability of Manual Muscle Testing Through the Comparison of Isokinetic Biodex
Testing About the Knee Joint
tJamie Hale, Samantha Namm, Jane Nguyen, Jeren Marquecho-Riley, Onofre Sunga
California State University of San Marcos
Running head: THE RELIABILITY OF MANUAL MUSCLE TESTING THROUGH THE
COMPARISON OF THE ISOKINETIC BIODEX TESTING ABOUT THE KNEE JOINT
Abstract
Manual muscle testing (MMT) is often used to test an individual’s muscle
strength or the ability of a specific muscle to perform against resistance. MMT may not
be reliable and could generate more antagonist activity. The purpose of this study was to
compare EMG activity of knee extension and flexion of the vastus medialis, vastus
lateralis, rectus femoris, and biceps femoris. EMG is commonly used to help diagnose
neuromusculoskeletal dysfunction. The Biodex is currently the gold standard for
measuring muscle strength. Subjects were 12 college students between the ages of 18-30
with no specific requirements. Surface EMG was placed on 4 muscles listed above and
subjects performed a total of 12 tests (3 manual extension, 3 manual flexion, 3 biodex
extension, and 3 biodex flexion) all about the knee joint. Using a T-test ran with the
standard deviations collected over a 2000 point series we found a significant difference
for one muscle, (Vastus Lateralis) during knee flexion (P=.029,P< .05). It was predicted
these values may occur as these are the antagonist muscles for knee flexion and the leg
may contract these muscle more during manual testing in an attempt to stabilize the leg.
It was hypothesized that the muscle manual test will be less reliable when compared to
the isokinetic dynamometer (Biodex) and will elicit greater antagonist muscle activity.
Introduction
Manual muscle testing (MMT) is often used to assist in diagnosing
neuromusculoskeletal dysfunction. Mild symmetrical muscle weakness is still difficult to
detect despite MMT common clinical usage due to that age, weight, height, and gender
affect strength (Schmitt et al., 2008). Three distinct muscles of the leg—such as the
quadriceps and hamstrings—are tested (Schmitt et al., 2008). There are several
limitations to MMT. One noted is if the tester maintains consistency in the starting
position. If this angle varies by more than a few degrees or half of an inch, the subject’s
line of force will alter and substitution of coactive muscle functions may take place
resulting in skewed EMG measurements (Schmitt et al., 2008). Another is if the tester
applies force too quickly and overpowers the subject. MMT assesses strength so the
tester must apply an increasing rate of force until the muscle begins to give (Schmitt et
al., 2008). An experienced tester will be able to sense this difference. The test is over
once the muscle is in motion.
Muscle activity during maximal isokinetic contraction is measured using
electromyography (EMG). The antagonist EMG measurements range from 10%-50% to
nearly 60% of the muscle when acting as an agonist during contraction (Kellis et al.,
1997). However, because there is no linear relationship between EMG activity and
muscle moment, this places a limitation on using normalized EMG measurements as a
representation of antagonist muscle function. To keep the knee joint stabilized during
isokinetic, concentric knee extensions, hamstrings and quadriceps coactivation must
take place (Kellis et al., 1997).
Running head: THE RELIABILITY OF MANUAL MUSCLE TESTING THROUGH THE
COMPARISON OF THE ISOKINETIC BIODEX TESTING ABOUT THE KNEE JOINT
In a comparative study of isokinetic dynamometry and MMT of ankle dorsal and
plantar flexors and knee extensors and flexors, 108 patients’ strength, who had either
diabetes or alcoholic liver cirrhosis, were compared to the control group, who were
made up of 90 healthy individuals (Andersen et al., 1997). The comparison found that
MMT underestimated the severity of muscle weakness than the isokinetic dynamometer
(Andersen et al., 1997). This may be a result of several limitations. Conversely, another
research study found a moderate to strong Pearson/Spearman correlation in the
strength measured by MMT (Bohannon, 2004). Yet, the sensitivity of MMT is lacking. It
was found that with as little as 50% of muscle strength measured, subjects were
classified as normal which leads to that MMT cannot clinically diagnose damage to the
muscle because it cannot distinguish differences (Bohannon, 2004). MMT can be used
for screening deficits in strength. MMT used in conjunction with the dynamometer
proved to be very effective in identifying strength deficits.
The isokinetic dynamometer is generally accepted as the gold standard in
measuring position, torque and velocity. A study was done to assess the dynamometer’s
mechanical reliability and validity. It was found that the concentric velocity was valid up
to 300 deg/sec and that this equipment can consistently reproduce measurements
across trials (Drouin et al., 2004).
With these two tests so widely accepted and used, the question of how accurate is
muscle manual testing arises. We hypothesize that the muscle manual test will be less
reliable when compared to the isokinetic dynamometer, and will elicit greater
antagonist muscle activity.
Methods
Subjects were 12 college students between the ages of 18-30. 6 males and 6
females,during a manual muscle test, performed 3 trials each with maximum effort for
extension upon the knee joint, and 3 trials for a maximum effort for flexion upon the
knee joint. Surface electromyographies (EMG) were placed on the vastus medialis,
vastus lateralis, rectus femoris, and biceps femoris carefully in hopes of gathering
sufficient muscle activity during each exercise. Subjects were then asked to do the same
procedure while strapped into the isokinetic biodex system 3 machine for maximum
effort through extension and flexion upon the knee joint. The Biodex was set at a rate of
thirty degrees per second for each movement involved, flexion and extension. There
were a total of 12 movements during this effort on achieving optimal muscle activity, for
both tests with extension and flexion at three trials each. The first two trials on each
muscle exercise were practice runs for the subjects to understand the effects of each
movement and the third was recorded for our study. All subjects were informed of
experimental procedures and gave their consent before participating. All procedures
were performed within the span of an hour on the same day, so no second visits were
held to promote variability in their muscles.
Running head: THE RELIABILITY OF MANUAL MUSCLE TESTING THROUGH THE
COMPARISON OF THE ISOKINETIC BIODEX TESTING ABOUT THE KNEE JOINT
Equipment
Isokinetic biodex system 3 machine with over the shoulder straps, waist strap,
right legged arm with ankle strap. Surface EMG, with 2 pads on each muscle listed as
well as a ground surface emg placed on the patella. Consistent manual muscle tester
with knee at an approximate 45 degree angle start position for both extension and
flexion.
Data Interpretation
The data from the EMG machine for the 4 muscles gave the muscle contraction
from the maximum force output for each individual muscle during each individual trial.
The first trial was considered a warm up trial, and the second trial was used as a practice
trial, and the third trial for each movement was used towards the data. For each subject,
the data was taken from the burst of each muscle during the 2 different movements on
both the manual test and biodex test. The standard deviation was taken from the
moment of greatest muscle force for about 2 seconds at the rate of 1000 Hz per second
(2000 Hz). Then a T-test was applied between the Biodex extension and the manual
extension as well as the Biodex flexion to the manual flexion testing. This gave a value,
which correlated the data against each other giving a percentage of the likelihood that in
those 2 separate tests the muscles acted in the same way for each muscle in all subjects.
A 5% difference between the manual muscle test and the biodex test for each muscle is
ideal in the support of the null hypothesis. This determined if there was a small
percentage that the muscles acted in the same way for both tests. If there was a less than
five percent difference then the tests were different, accepting the null hypothesis. If
there was a greater than five percent difference the tests were relatively the same,
declining the null hypothesis that they are different. The mean was then taken for each
different muscle and each separate test in each different subject. This data collected was
put into a bar graph to determine the correlation between the 2 tests as well as a series
error bar to illustrate a graphical representation of the variability of data and use of
graphs to indicate the error in a reported measurement. See graphs for demonstration.
Results
Data from the third trial of each subject was used to find the standard deviations.
The standard deviations were calculated by using data over a period of 2000 series
points. EMG data was collected at 1000 HZ for both the biodex test and the manual test.
The means of EMG (taken in volts) indicating muscle contraction was taken for 4
muscles. The mean volts recorded for the Vastus Medialis was similar for Biodex
extension and manual extension (M=.144, M=.148). The mean found for biodex flexion
and for the manual test for this muscle was also slightly similar (M= .031,M=.021).
Vastus Lateralis averages were the same for extension (M= .148 and M=.148) but
showed differences showed in flexion (M=.027, M=.012). Means for Rectus Femoris
Running head: THE RELIABILITY OF MANUAL MUSCLE TESTING THROUGH THE
COMPARISON OF THE ISOKINETIC BIODEX TESTING ABOUT THE KNEE JOINT
were similar for extension (M=.167,M=.183) while flexion showed slight differences
(M=.027, M= .012). Lastly, averages for Biceps Femoris muscles were similar
(M=.027,M=.024) for extension and flexion (M=172,M= .168). Using a T-test ran with
the standard deviations collected over the 2000 series points we found only a significant
difference between the two test types for one muscle, the Vastus Lateralis when assessed
for knee flexion (P=.029,P< .05). The P-value for the Vastus Medialis was close to
showing a significant difference at (P=.07 ,P< .05).
Discussion
The purpose of this study was to compare EMG activity of knee extension and
flexion of the vastus medialis, vastus lateralis, rectus femoris, and biceps femoris. The
results suggest that manual testing is as reliable as the Biodex testing when performing
knee flexion and extension. The manual and Biodex tests revealed similar muscle
activation output. When MMT and the Biodex EMG output data’s mean and standard
deviation values were compared, the Biodex testing numbers were slightly higher,
showing that the Biodex testing showed more contraction activity when flexion and
extension were assessed. During knee extension in both tests, the biceps femoris showed
a low EMG score. It was hypothesized that the muscle manual test will be a less reliable
method of testing when compared to the isokinetic dynamometer (Biodex), and will
elicit greater antagonist muscle activity because of instability. This study showed that
the vastus lateralis and vastus medialis during knee flexion for the two different
conditions, did in fact have more contraction due to instability from the results having a
significant difference value of (P=.029,P< .05) and (P=.07 ,P< .05). However, after
analyzing the mean for contractions in these two muscles it was recognized that this
significant difference came with the increase contraction of the muscles during biodex
testing rather than the manual tests proving the hypothesis incorrect. All other results
for the other 3 muscles during different conditions of this study did not support the
hypothesis because the “P-values” were above a 5% difference.
These findings are applicable to an individual who may have been afflicted by an
injury or some sort of deficiency. By having a MMT screening run, it will be able to
determine which muscle was most affected. MMT is also easily accessible rather than its
counterpart, the Biodex for the reason that they are expensive and not portable. MMT is
considered a reliable screening test from this study, but it has some limitations. One
limitation is if the tester maintained consistency in the start position for each trial. If the
start position angle differed by more than a few degrees than the subject’s line of force
would also differ, making the muscles that are supposed to perform work change and
skew the EMG data (Schmitt et al., 2008). Some disadvantages in the usage of Surface
EMG include only being able to record superficial muscles and large muscle groups and
may not be selective enough for detailed or smaller muscles. Surface EMG is more prone
to crosstalk, the electrical activity from neighboring muscles, as well as movement
artifact and contact pressure fluctuations that can hinder the impulse of an individual
Running head: THE RELIABILITY OF MANUAL MUSCLE TESTING THROUGH THE
COMPARISON OF THE ISOKINETIC BIODEX TESTING ABOUT THE KNEE JOINT
muscle unit. This may have affected some results.
The biodex chair was used for both tests to reduce a knee angle variable that may
affect contraction quantity. The same tester was also used for all manual tests to reduce
differences. Another problem that may affect the results was that an isometric test was
done during manual testing where a concentric and eccentric test was performed with
the biodex providing resistance throughout full range of motion. The stable nature of the
biodex allowed the antagonist muscles to better reflect the co-contraction that naturally
occurs in the leg during flexion and extension, thus would seem to be more reliable in
determining force output of the leg as a whole. However, this study would require more
testing with the use of a force sensor to determine accuracy of force output of the upper
leg muscles. The rest periods between trials also could have increased from 2 minutes to
5 minutes to ensure full recovery. The slight differences in muscle activity may have
been due to electrode placement or a learning effect created by subjects being unfamiliar
with the biodex machine and thus exerting more than exerted on a human tester .
Overall, the manual test compared to the biodex test resulted in similar means per
muscle with only a slight difference seen in antagonist muscle groups during flexion.
The study did not show a significant amount of difference in muscle contraction activity
and the manual test would appear accurate disregarding overall force output. A test
determining force output would most likely be required to develop a rehabilitative
program for an injured subject but a manual test seems to be indicative of a difference in
specific muscle contraction. The results that were in this study collected were
unsupportive of the hypothesis, proving that a manual muscle test with surface EMG is a
valid form for assessing muscle strength and ability.
Running head: THE RELIABILITY OF MANUAL MUSCLE TESTING THROUGH THE
COMPARISON OF THE ISOKINETIC BIODEX TESTING ABOUT THE KNEE JOINT
Works Cited
Andersen, H., Jakobsen, J. (1997). A Comparitive Study of Isokinetic
Dynamometry and Manual Muscle Testing of Ankle Dorsal and Plantar
Flexors and Knee Extensors and Flexors.
Bohannon, R. (2004, Nov. 4). Manual Muscle Testing: Does It Meet the
Standards of an Adequate Screening Test?.
Drouin, J., Valovich-McLeod, T., Shultz, S., Gansneder, B., Perrin, D. (2004).
Reliability and Validity of the Biodex System 3 Pro Isokinetic
Dynamometer Velocity, Torque, and Position Measurements.
Kellis, E., Baltzopoulos, V. (1997). The Effects of Antagonist Moment On the
Resultant Knee Joint Moment During Isokinetic Testing of the Knee
Extensors.
Schmitt, W., Cuthbert, S. (2008, June 2). Common Errors and Clinical
Guidelines for Manual Muscle Testing: “The Arm Test” and Other
Inaccurate Procedures.