2- Measurement of Muscle Performance With Instrument

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 - [email protected]

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.


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.



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?



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.



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.



We have avoided using term

strength and prefer using

muscle performance.

We can measure muscle

performance isokinetically,

isometrically, etc.



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.


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



Redefinition of terms adds nothing to

our understanding muscle

performance (assessment of power

during isokinetic high speed or low

speed testing).



Which of the units (force, torque, power or

work) best describes muscle performance?

That will depend on the reason muscle

performance is being measured.



Therapist must ask what aspect of

muscle performance needs

assessment?

Therapist need understanding of

muscle biology and kinesiology.


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.



We cannot measure muscle tension in

humans but measure force created

when muscle tension acts through

skeletal leverage system.



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.



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 90than at 120of flexion- even though there could be more tension developed at 120 of flexion.


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.


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.


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 subjects 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.


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.


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.


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


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.


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.


CABLE TENSIOMETERS

The tensiometer is placed at

some point between the two

sites of fixation. As a cable is

pulled, it presses on the

tensiometers rises (a bar)

which is connected to a gauge

that measures in relative

units.


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


RELIABILITY

Clarkes 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


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.


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.


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.


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.


STRAIN-GAUGE DEVICE


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.


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 ( Ohms Law) as a function

of the applied load.


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


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.


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


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.


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)


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).


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.


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).


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.


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.


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.


QUISTIONS?????

10/16/2011 Dr. Amal Hassan Mohammed Ibrahim -

[email protected]

2- Measurement of Muscle Performance With Instrument

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