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LECTURE II
DR. AMAL HM. IBRAHIM
Measurement of Muscle
Performance With Instrument
INTRODUCTION
In this lecture we will emphasis on
clinical practice and selective
review of literature.
10/16/2011 Dr. Amal Hassan Mohammed Ibrahim -
INTRODUCTION
Muscle testing to be meaningful it must
reflect muscle performance and not other
variables.
We test muscle to determine patient
restrictions and collect information that will
help us make decisions. The most common
decision is whether or not we want to exercise
specific muscles.
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STRENGTH AND WEAKNESS
The terms used most often to describe muscle
performance are “strength “ and “weakness”,
both have no units of measurement.
The only definition of strength suggest that it
is the maximal force can be exerted during a
single isometric contraction.
This definition implies that all other forms of
measurement (isokinetic, manual muscle test)
do not assess strength.
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STRENGTH AND WEAKNESS
If someone tells you they have measured
strength.
Do you know what they did?
Do you know what units they obtained?
Did they measure force, torque, or power?
Under what conditions and with what type of
device did they measure?
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STRENGTH AND WEAKNESS
Using the term “strength” give a false
impression that the same thing is being
measured in the same way.
A fundamental question in muscle
assessment concerns the best approach to
measurement.
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STRENGTH AND WEAKNESS
Are force measurement better than torque?
Does use of one type of device or one type of
contraction tell us more than use of another?
From publications we found many authors
said they measuring strength. The authors
were not measuring the same thing but they
all described what they were measuring by
using the same term.
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STRENGTH AND WEAKNESS
We have avoided using term
“strength” and prefer using
“muscle performance”.
We can measure muscle
performance isokinetically,
isometrically, etc.
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STRENGTH AND WEAKNESS
“Weakness” obviously depends on a
definition of strength.
There are lack of data that can be used
to make judgment.
We should use terms which indicate that
we are expressing opinion not terms that
imply documented levels of
performance.
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UNITS OF MEASUREMENT
One of the advantages of using instrument to measure muscle performance is that they yield units that have universal meaning.
If you are measuring force although you may use English or metric units, it is always:
force= mass X acceleration.
work = force X distance.
power = work X time.
Torque = force X perpendicular distance from the axis of rotation
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UNITS OF MEASUREMENT
Redefinition of terms adds nothing to
our understanding muscle
performance (assessment of power
during isokinetic high speed or low
speed testing).
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UNITS OF MEASUREMENT
Which of the units (force, torque, power or
work) best describes muscle performance?
That will depend on the reason muscle
performance is being measured.
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UNITS OF MEASUREMENT
Therapist must ask what aspect of
muscle performance needs
assessment?
Therapist need understanding of
muscle biology and kinesiology.
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MUSCLE BIOLOGY AND KINESIOLOGY
Muscle has been described as a
physiological transducer of chemical
energy (ATP) to mechanical (muscle
tension).
Tension is actually a type of force that
can be measured by instrument (usually
a strain gauge) which must be attached
to the muscle or tendon.
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MUSCLE BIOLOGY AND KINESIOLOGY
We cannot measure muscle tension in
humans but measure force created
when muscle tension acts through
skeletal leverage system.
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MUSCLE BIOLOGY AND KINESIOLOGY
Forces and torques will vary because of biomechanical factors ( changes in angle of insertion, rotational and compression components).
Forces and tension are both vectors (have magnitude, direction, a line of application and angle of application).
Forces and torques are consistently reflect tension during isometric contraction.
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MUSCLE BIOLOGY AND KINESIOLOGY
when we assess muscle, we are measuring
forces of which only the magnitude element
varies.
example: biomechanically biceps brachii might
measure more force with elbow 90°than at
120°of flexion- even though there could be
more tension developed at 120° of flexion.
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SPEED OF MOVEMENT AND SPEED OF
CONTRACTION
When a limb moves, we can measure its
speed or with isokinetic devices we can
control the angular speed.
The rate of tension development is speed
of contraction.
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SPEED OF MOVEMENT AND SPEED OF
CONTRACTION
Two legs may be moving through an arc with
the same speed of movement. but if one has a
greater mass, it will develop more tension per
unit time to move the heavier limb at the same
speed as the lighter limb.
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TORQUE AND FORCE
It is better to measure force, which is a linear quantity, or to use the rotational measurement, which is torque?
Measurement of force using cable tensiometer or hand-held dynamometer.
Torque is difficult to drive unless a device is used has an axis of rotation aligned with the subject’s anatomical axis of rotation. But we can measure torque from (force X distance between resistance and axis of rotation).
Muscle torque can only be estimated by calculating from anatomical studies.
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ISSUES
Muscle contraction have been described as
eccentric, isometric, or concentric.
Greatest tension per unit of muscle can be
generated eccentrically, less can be generated
isometrically and less concentrically.
Eccentric contraction use less metabolic energy
(ATP) per unit of tension than do other
contractions.
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ISSUES
when we assess muscles, we must be aware of
the type of contraction we are measuring.
a major clinical concern is whether the
performance in any one mode reflects the
others and whether training in one mode
increases performance in the others, we do not
know the answer.
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ASSESSMENT CRITERIA
Comparison between “affected” and “non
affected” limbs may be useful, but there are no
data that tell us how much inter-limb variation
is normal.
We advocate good clinical sense- that is we
urge clinicians to use all available data and not
to be tempted to relay on questionable criterion
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ASSESSMENT CRITERIA
Some forms of fatigue tests measure the number of contractions it takes before a subject reaches a percentage of their maximal force or torque. Although such an index may reflect on a relative basis the biological properties of muscle that relate to “endurance”
The problem arises because “fatigue” and “endurance” lack clinically applicable operational definitions.
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CABLE TENSIOMETERS
Cable tensiometers are
used to test muscle
performance, one end
of the cable is
attached to some fixed
(stable) object and the
other end is attached
to a limb segment.
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CABLE TENSIOMETERS
The tensiometer is placed at
some point between the two
sites of fixation. As a cable is
pulled, it presses on the
tensiometer’s rises (a bar)
which is connected to a gauge
that measures in relative
units.
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CABLE TENSIOMETERS
The cable must be fixed
to immovable object (a
wall, column, or floor).
The other end of the
cable must be attached
to whatever body
segment is being tested.
The cable must be in the
plane of the movement
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RELIABILITY
Clarke’s systemic investigation tested 64 subjects twice within a single session by two different examiners not specified.
The paired measures (the values obtained by each examiner) were correlated.
Clarke states that coefficients of 0.90 or greater are (desirable) whereas coefficients as low as 0.80 indicate that the test can be used for individual measurements
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RELIABILITY
Alderman and Banfield tested the reliability of
cable tensiometer for three sets of muscles
(knee extension, elbow flexion and extension)
were tested bilaterally in 32 male using
modified Hettinger chair for stabilization.
The inter tester reliability are reasonably in
agreement with Clarke.
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VALIDITY
Clarke compared cable tensiometer, a Wakim-porter strain gauge, a spring scale, and a Newman Myometer on the basis of which instrument were the most reliable and equivalent.
Finger flexion, wrist dorsal flexion, shoulder outward rotation, neck extension, knee extension and ankle planter flexion were examined as strong or weak.
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VALIDITY
The cable tensiometer and strain gauge were used
for al tests, whole spring scale was used to
examine shoulder rotation and neck extension
only.
The myometer was used only for wrist and finger
tests.
Clarke argued that strain gauge was less useful
because it was too sensitive and other two devices
had limited application for many muscles.
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VALIDITY
The tensiometer was the best overall
instrument. This conclusion is clearly
based on his subjective observations
relative to the ease of application of
the various instruments rather than
on reported data.
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STRAIN-GAUGE DEVICES
Used for muscle performance measurement
with great differences in design, electronics
and methods of application.
Loads (tension, compression, or shear)
applied to material cause a change
(deformation) called strain which is
measurable.
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STRAIN-GAUGE DEVICES
Strain gauge are made of electroconductive material and are usually
applied to the surfaces of finely machined metal ring or rods. When
load is applied to the ring, the metal deforms with strain gauge leading
to a change in the electrical resistance of the gauge. The current or
voltage passed through the gauge will vary ( Ohm’s Law) as a function
of the applied load.
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Various strain gauge designs in the form of
geometrically formed foil made of conductive material.
Foil must be positioned on the supporting surface, to
achieve sensitivity to the application of force in the
desired direction
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MUSCLE EVALUATION BY STRAIN GAUGE
Strain gauge devices have been most often used for
muscle evaluation by having the metal ring
attached to an object that a limb segment can
either push or pull against (creating either
compressive or tensile strain).
If the device is calibrated, the voltage or current
change can be converted into measurements of
force.
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Other uses of strain gauge
The basic system FDM-T consists of a
treadmill ergometer with an integrated,
calibrated measuring sensor. The sensor
element itself consists of numerous high-
quality capacitive force sensors. On a
treading area of 150 x 50 cm the sensor
unit comprises more than 5000 pressure
/ force sensor
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DYNATRON PINCH GAUGE Using The Same Accurate Gauge As The
Hand Dynamometer, The Dynatron Pinch
Gauge Measures Forces Up To 45-lbs/20 Kg.
Peak/hold Needle Stays At The Highest
Reading Until Reset. Wrist Strap For
Practitioner To Hold Gauge While Testing.
Comes In A Padded Case.
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THE DIFFERENCES
BETWEEN VARIOUS TYPES
OF STRAIN GAUGE
The manner in which the
voltage or current change
is displayed (strip-chart,
digital displays, or
voltmeter).
Application of device to the
limb segment ( push or
pull)
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THE DIFFERENCES
BETWEEN VARIOUS TYPES
OF STRAIN GAUGE The type of interfaces used to connect limb
segments (cuffs, pads, or straps).
Methods of applications (easy in use or
difficult).
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RELIABILITY OF STRAIN GAUGE
Asmussen and his colleagues used five
different strain gauge dynamometers to
demonstrate that the force measurement
obtained were replicable.
Six muscle groups in 50 normal young men
were tested twice (forward and backward
trunk flexion, downward pull of the arm,
hand grip, knee flexion and extension).
Reliability coefficient ranged from .91 to .96
with no report about statistical method used.
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RELIABILITY OF STRAIN GAUGE
Clarke compared the reliability of cable
tensiometer and the Wakim-porter strain gauge of
six muscle group in 64 nondisabled male college
students. Tests were also performed with a spring
scale and a myometer for some muscles.
The results of test- retest correlation were very
similar to cable tensiometer results (ranged from
.81 to.94).
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CAUSES OF ERRORS IN STRAIN GAUGE
Limb must either push or pull and in the
same line.
The application during different tests must
be identical.
Stabilization of the limbs must be
maintained to localize force measurement
only to that muscle tested.
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VALIDITY
Some investigators imply validity
because strain gauge instrument
accurately reflect applied load.
The comparisons with loads and
tensiometers have been used to justify
the use of strain-gauge devices to
measure muscle performance.
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VALIDITY
The strain gauge can be applied to
objectify the subjective test as manual
muscle test.
Validating one test by comparing it with
another test is legitimate.
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