surface electrode emg
TRANSCRIPT
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Surface Electromyography
(SEMG)
Presented By:
Joseph S. Ferezy, D.C.
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Initially, Claims Made by theManufacturers Were Frankly
Outrageous, and It Was Easy toBrush Paraspinal EMG off As
Useless.
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More Recently, However,
Literature Is Beginning to
Accumulate, and Manufacturers
Appear to Have Upgraded theQuality of the Equipment While
Downgrading the Claims.
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When the Doctor Looks for
Answers, It Seems That Only the
Manufacturers and DistributorsAre Supplying Them.
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The Purpose of This Presentation
Is to Sift Through the Claims,
and Examine the FactsRegarding Paraspinal EMG.
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You Should Not Consider
Buying a Device WhichMeasures Something If You
Cannot Answer Three Questions: What Am I Measuring, and What Is Known
About It?
Is the Device Giving Me an Accurate Measure?
What Useful Clinical Information Can BeGleaned From This Measurement?
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This Weekend, I Will Attempt to
Present the Facts Necessary toThink Through Each of the
Above Questions. In Doing So,Each of You Will Be Able to
Make up His/her Own Mind, and
Not Just Listen to My Opinions.
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Without This Requisite
Background, One Has No
Chance at All of Critically
Examining the Utility of ThisTechnology, in Regard to Their
Personal Clinical Needs.
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There Are Numerous Problems Which
Must Be Overcome Before One Can Say
That They Can "Measure Spasm". WhatExactly Is a Spasm? There Is an
Embarrassing Lack of Information
Related to Measuring Muscle Spasm,and the One Study of Interexaminer
Reliability Shows Lousy
Reproducibility. Ironically, Our
Assessment of It Significantly Effect the
Lives of Millions of People Each Year.
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Surface Electrodes
"What Is Better, Surface Electrodes or
Needle Electrodes?"
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This Is Really an Apples and
Oranges Question, or at Least a
Question Which Is
Oversimplified And, Hence,
Unanswerable. For WhatPurpose Is the Electrode Is Being
Used? It Would Be QuitePainful to Look for Insertional
Activity With a Surface
Electrode.
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It Is Generally Accepted That a
Surface Electrode Is Superior for
the Assessment of Global
Myoelectric Activity. If You
Are Looking for GeneralActivity of Muscle Tissue in a
Particular Area, the SurfaceElectrode Is Superior.
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If You Are, However, Looking
for Information Regarding aSpecific Piece of a Specific
Muscle, Then a Needle or Wire
Has an Obvious Advantage. In
Fact, Even Tiny Movements (.1
Mm) Can Significantly Alter theDay to Day Reliability of Needle
Electrodes.
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Most Equipment Manufacturers Will
State That Surface Electrodes Are More
Reliable, and Site Papers As Sources of
Proven Reliability (Reproducibility). It
Should Be Noted That Virtually All of
These Studies Regard Peripheral
Musculature. Spector at New York
Chiropractic College Did Do a Very
Good Study on Paraspinal Muscles and
Attached Surface Electrodes, Reporting
Excellent Reliability Coefficients.
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If the Readings From Attached
Surface Electrodes Are Reliable,
We Must Next Ask How Does
the Procedure of "Scanning"Emg Compare to Attached
Surface Electrodes.
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Thompson Et. Al. And the Mayo
Clinic Study Are Often Sited As
Proof of Scanning Electrode
Reliability As Compared to
Attached Surface Electrodes.Attached Surface Electrodes
Were Never Even Used in ThisStudy.
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Thompson Was Attempting to
See If a 2 Second Average of
Integrated (MAP) Was Sufficient
for a Reliable Reading. His
Conclusion Was That It WasNot. He States That Only 37%
of the Sites Sampled Fell Withinan Acceptable Range With a
Two Second Scan.
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One of His Conclusions Stated, "a
Longer Integration Period Enhances
the Validity" and "A 10 SecondIntegration Period Would Improve
the Quality of the Data Obtained..."
This Raises a Significant QuestionAs to the Reliability of Scanning
Electrodes. A Properly DesignedReliability Study for Scanning
Electrodes Versus Attached Surface
Electrodes Should Be Undertaken.
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Once the Issue of Reliability Is
Addressed, One Must Ask If the
Reading Is an Accurate
Reflection of Myoelectric
Activity. To Determine This, LetUs First Consider Variables
Regarding Apparatus Detectionand Recording of Signals.
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Basmajian and Deluca
"It Is Important to Remember That the
Characteristics of the Observed EMG
Signal Are a Function of the ApparatusUsed to Acquire the Signal As Well As the
Electrical Current Which Is Generated by
the Membrane of the Muscle Fibers".
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If the Filter Is Narrow at the
Point of Signal Acquisition, It
Does Not Matter What Band
Width Is Available From ThatPoint on. Like a Funnel Turned
Upside Down.
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Tissue Filtering
The Amplitude of Action
Potentials Decreases to
25% Within 100 um.
The Thickness of the
Fatty and Skin Tissues
Must Also Be
Considered.
The Tissue(s) Behaves
As a Low-pass FilterWhose Bandwidth and
Gain Decreases As the
Distance Increases.
The Muscle Tissue Is Highly
Anisotropic. Orientation of
the Detection Surfaces of theElectrode With Respect to
the Length of the Muscle
Fibers Is Critical.
Dirt, Oils, Etc. Must Be
Removed From the Skin, So
That They Do Not Distort
the Signal. This Can Be
Accomplished by Cleaning
the Skin With an Abrasive,Or, Minimally Wipe It With
Alcohol and Allowed to Dry
Prior to Taking a Reading.
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Electrode-electrolyte Interface
Behaves As a High-pass Filter. The Gain
and Bandwidth Will Be a Function of the
Area of the Detection Surfaces,Electrolytic Treatment of the Surfaces, and
Any Chemical-electrical Alteration of the
Junction. The Detection Surfaces Should Always Be
Kept Clean.
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Bipolar Electrode Configuration
This Property Ideally Behaves As a Band-passFilter. However, This Is Only True If the Inputs tothe Amplifier Are Balanced and If the Filtering
Aspects of the Electrode-electrolyte Junctions AreEquivalent.
A Larger Interdetection Surface Spacing WillRender a Lower Band-width. This Aspect Is
Particularly Significant for Surface Electrodes. The Greater the Interdetection Surface Spacing,
the Greater the Susceptibility of the Electrode toDetecting Measurable Amplitudes of Emg Signals
From Adjacent and Deep Muscles.
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Bipolar Electrode Configuration
A Rule of Thumb Is That the Electrodes Will
Detect Measurable Signals From a Distance
Equal to the Interdetection Surfaces Spacing.However, the Anisotropy of the Tissues Beneath
the Electrode May Augment the Sensitivity of
the Electrodes Along the Surface of the Muscle
Creating Cross-talk.
An Interdetection Surface Spacing of 1.0 Cm Is
Recommended for Surface Electrodes.
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Amplifier Characteristics
Values Should Minimally Distort the EMG
Signal Detected by the Electrodes.
Length of the Leads to the Preamp Should
Be As Short As Possible and Should Not
Be Susceptible to Movement. The
Necessity of This Precaution IsAccentuated When Amplifiers With High
Input Impedance Are Used.
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Typical Settings and
Characteristics for the Amplifier Gain: Such That It Renders
the Output With an
Amplitude of Approximately
+- 1v. Input Impedance > 10-12
Ohms Resistance in Parallel
With 5 Pf Capacitance.
Common Mode Rejection
Ratio: > 100 db.
Input Bias Current: As Low
As Possible (Typically Less
Than 50 Pa).
Noise < 5uv RMS.
Bandwidth (3 Db Pointsfor 12 Db/octave
Rolloff).
Surface Electrodes 20-500 Hz.
Wire Electrodes 20-1000
Hz. Monopolar and Bipolar
Needle Electrodes forGeneral Use - 20-1000
Hz.
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The Bandwidth Filter of the Amplifier Is
a Point of Contention Among
Manufacturers. Median Frequency of
the Power Density Spectrum Appears to
Provide an Appropriate Representation
of Biochemical Events Within the
Muscle. It Is Well Documented That in
Sustained, Constant Force IsometricContraction, a Shift Toward Lower
Median Frequencies Occurs, As the
Muscle Fatigues.
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Along With Decreasing
Frequency Is an Increase in
Amplitude. These Phenomenon
May Be Due to Recruitment of
Muscle Fibers, Motor UnitSynchronization, And/or
Conduction Velocity Changes ofMuscle Fibers.
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One Must Carefully Define the
Term "Muscle Fatigue" Before
Determining How the
Phenomena of Greater
Amplitude and Lower Frequencyof Emg Signal During Active
Voluntary Muscle ContractionCan Be Clinically Applied.
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Physiologically, Muscle Fatigue
Does Not Happen All at Once.
Histologically There Is No
"Point of Fatigue", Just a
Continuum of Chemical ChangesLeading to an Eventual Clinical
Failure of the Patient to Performthe Task.
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The Emg Signal Under
Voluntary Muscular Activity
Has Been Extensively Studied.
It Is Expressed As a Percent of
(MVC). It Holds ExcellentProspects for Clinical
Application in Assessment ofBack Pain Patients.
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Whether This Is the Same As
"Spasm" Is Doubtful.
Methodology for Signal
Acquisition Must Be
Meticulously Performed,"Placement Determination by
Bony Landmarks IsUnacceptable".
Roy and Deluca
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Other Considerations
It Is Preferable to Have the Subject, the
Electrode, and the Recording Equipment in an
Electromagnetically Quiet Environment. However, If All the Procedures and Cautions
Discussed Are Followed and Heeded, High
Quality Recordings Will Be Obtained in the
Electromagnetic Environments Found in Most
Institutions, Including Hospitals.
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Where To Locate The Electrode
If One Is Measuring EMG Frequency
Parameters, It Is Essential to Avoid
Placement of the Electrode Near the MotorPoint.
Signal-to-noise Ratio.
Signal Stability (Reliability).
Cross-talk From Adjacent Muscles.
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A Recent Article by Wolfe,
Wolfe and Segal From Emory
University Reveals That
"Extraneous Movements Such
As Neck Flexion and PelvicRotation Can Elicit Profound
Activity From PercutaneouslyPlaced EMG Electrodes While
Little Change Is Seen at the Skin
Surface."
S Ti Fil i El d
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So, Tissue Filtering, Electrode-
electrolyte Interface (Skin Preparation),
Electrode Configuration, AmplifierCharacteristics, Recording
Characteristics, Electrode Location and
Other Considerations Will All Effect theAccuracy of the Signal Being Measured.
It Is Important to Check Into
Manufacturers Specifications andApproaches to Each of These Variables,
and See If They Are Satisfactorily
Considered.
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What Useful Information Can Be
Obtained By Measuring Global
Myoelectric Activity?
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This Is a Difficult Question to
Answer. Much Available LiteratureIs Not Published in Peer Reviewed,
Referred Journals and Even the
Referenced Literature Is Filled WithQuestionable Methodologies,
Contradictions and Hardware
Considerations. Let Us Begin With
a Review What Is Known Regarding
Paraspinal Muscle Function.
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Commonly They Comprise (From
Superficial to Deep): the
Semispinales, the Multifidi, and the
Rotatores Muscles.
Some Contend That Deep RotatorMuscle Paralysis Is the Cause of
Idiopathic Scoliosis. It Has Been
Demonstrated That There IsIncreased Muscular Activity on the
Convex Side of the Scoliotic Curve.
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As the Slowly Flexing Trunk Is Lowered, the
Activity in Erector Spinae Increases Apace
and Then Decreases to Quiescence WhenFull Flexion Is Reached. If an Attempt Is
Made Then to Force Flexion Further, Silence
Continues to Prevail in the Erector. In FullFlexion, Then, the Weight of the Torso Is
Borne by the Posterior Ligaments and
Fasciae-the Posterior Common Ligament, the
Ligamentum Flavum, the Interspinous
Ligaments, and the Thick Dorsal
Aponeurosis.
i h h bj di h
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With the Subject Standing, the
Activity in Erector Spinae
Ceases Earlier During Forward
Bending Than It Does When
Seated. In Some Patients TheyFind Complete Relaxation in the
Sitting but Not the StandingPosture.
S di A i i i h
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In Standing Erect, Activity in the
Erector Spinae Is Not Required,
Except for Forced Extension. In
the Initial Stages of Flexion of
the Trunk in Bending Forward,the Movement Is Controlled by
the Intrinsic Muscles of theBack.
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It Has Also Been Shown That
the Position of Full FlexionWhile Seated (Slouching) Is
Maintained Comfortably for
Long Periods and That During
This Time the Erector Spinae
Remains Relaxed.
S bj S di i
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In Most Subjects Standing in a
Relaxed Erect Posture Showed a
"Low Level of Discharge" in the
Erector Spinae. Small
Adjustments of the Position ofthe Head, Shoulders, or Hands
Could Be Made Which WouldAbolish the Activity of the
Muscle, I.E., An Equilibrium or
Balance Could Be Achieved.
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From the Easy Upright Posture,It Has Been Found That
Extension (Hyperextension) of
the Trunk Is Initiated, As a Rule,
by a Short Burst of Activity.
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While Standing Upright
Flexion of the Trunk to One Side IsAccompanied by Activity of the Erector Spinaeof the Opposite Side "Antagonist.
If the Back Is Already Arched in Hyper-extension, Not Even This Sort of ActivityOccurs.
The Recording of Activity From Both Right andLeft Erectores During Bending to Either SideHas Also Been Shown, and There Is a Pattern ofCooperative Activity and Not a Simple
Simultaneous Antagonism.
Erectores Spinae Contract
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Erectores Spinae Contract(Vigorously) During Coughing
and Straining. This Occurs Evenin the Midst of Their Normal
Silence, Whether the Subject Is
Erect or "Full-flexed." The
Clinical Implications of This
Last Observation Should BeExplored.
It Has Also Been Reported That the
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It Has Also Been Reported That the
Erector Spinae Remained Relaxed
During the Initial Movement ofLifting Weights of up to 56 Lbs. It
Is Movement at the Hip Joint That
Accounts for the Earliest Phase ofApparent Extension of the Trunk.
However, the Ligaments of the BackWere Required to Carry the Added
Weight Without Help From the
Adjacent Muscles.
D i th P f f V i
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During the Performance of Various
Trunk Movements, Deep Muscles
Showed Patterns of Activity ThatClearly Showed Two Functions,
Sometimes They Initiate Movement,
and at Other Times They Stabilize
the Trunk. Almost All the
Movements Recruit All the Musclesof the Back in a Variety of Patterns,
Although the Predominance of
Certain Muscles Is Also Obvious.
In Compound Movements, When Subjects
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In Compound Movements, When Subjects
Are Not Trying to Relax, There Is Constantly
More Activity Than When the Movement Is
Carried Out Deliberately and WithConscious Effort to Avoid Unnecessary
Activity of Muscles. Complete Relaxation
and Lower Levels of Contraction Are the"Ideal" Rather Than the Rule for Normal
Bending Movements. Muscles That Might
Be Expected to Return the Spine to theVertical Position Often Remain Quiet; That
Suggests That Such Factors As Ligaments
and Passive Muscle Elasticity Play anImportant Role.
A Position of Complete Silence
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A Position of Complete Silence
Is Easily Found for Iliocostalis in
the Erect Position, but WithSlight Forward Swaying Activity
Is Instantly Recruited. ForwardFlexion and Rotation in the
Flexed Position Bring Out Its
Strongest Contractions, but It Is
Also Fairly Active in Most
Movements of the Spine.
Multifidus and Rotatores Have
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Multifidus and Rotatores Have
Rather Similar but Not Identical
Activity. With Movements in theSagittal Plane, They Are Active As
They Also Are in Contralateral
Rotary Movements. Yet, Like All
the Other Muscles, These Too Relax
Almost Completely During FullFlexion, Leaving the Trunk
Practically Hanging on Its
Ligaments.
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In a Systematic Exploration of the
Intrinsic Muscle of the Spinal
Column During Various Exercises
Widely Advocated for Physical
Fitness, It Was Found That theSemispinalis Capitis and Cervicis
Apparently Help to Support the
Head by Continuous Activity DuringUpright Posture. This Finding
Contradicts Other Studies.
In Almost All Vigorous Exercises
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gPerformed From the Orthograde
Position, It Has Been Found That the
Most Active Muscle Is Spinalis; Next inOrder Is Longissimus, and Least Active
Is the Iliocostalis Lumborum.
Nevertheless All Three Muscles and the
Main Mass of Erector Spinae Act
Powerfully During Strong Arching of
the Back in the Prone Posture. During
Push-ups, There Is Considerable
Individual Variation But, Typically, theLower Back Muscles Remain Relaxed.
mp e e- en ng xerc ses o
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p gthe Trunk Do Not Recruit Erector
Spinae As Long As There Is No
Concomitant Backward or Forward
Bending. This Clearly Refutes
Earlier Opinions Whose AuthorsHad Ignored Movements in the
Ventrodorsal Plane That Do Involve
Erector Spinae. Much of This WorkHas Been Confirmed, and the
Technique Has Been Adopted for
Er onomics b Tichauer.
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Deep Muscles
Variations in the Pattern of ActivityDuring Forward Flexion, Extension, and
Axial Rotation Suggest That theTransversospinal Muscles Adjust theMotion Between Individual Vertebrae.
The Experimental Evidence Confirms the
Anatomical Hypothesis That the MultifidiAre Stabilizers Rather Than Prime Moversof the Whole Vertebral Column
Th I t t ti f El t i l A ti it
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The Interpretation of Electrical Activity
Presents Some Difficulties. Did a Muscle
Showing Activity Produce the Movement,Prevent the Movement, or Was It
Contracting Isometrically? Therefore
Emphasis Must Be Placed on the Occurrenceof Electrical Silence, Knowing That the
Muscle Tested Was Not Taking Part in the
Movement Under Observation. Decreasing
or Increasing Activity During a Movement
Also Seemed to Be Functionally More
Important Than Unchanging Activity.
One Study by Anderson Et Al Attempted to
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One Study by Anderson Et. Al. Attempted to
Relate Paravertebral Muscle Function to Disc
Pressures, and Found That the Amplitude of the
EMG Signal and Pressure Increased Both WithAngles of Forward Flexion and With Increasingly
Static Loads in Flexion. During Asymmetric
Loading, Pressure Values and MyoelectricActivity Increased, Being Greater on the
Contralateral Side of the Lumbar Region and
Ipsilateral Side of the Thoracic Region. The Disc
Pressure, Intraabdominal Pressure, and Semi-integrated Rectified EMG Signal Were Higher
Throughout When the Trunk Was Loaded in
Rotation, Rather Than in Lateral Flexion.
Changes in the Lumbar
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g
Curvatures During Sitting and
Standing Lumbar Muscles Have Been Shown to Be Inactive
During Relaxed Sitting but Showed Some Activity in
Straight Sitting and in the Standing Posture.
This Finding Is in Agreement With the Results of Most
Other Workers.
Disc Pressure and Myoelectric Activity Change
Together. When the Back of a Seated Subject Is
Supported, Levels of Both Pressure and EMG Signal
Fall. In This Study It Was Confirmed That
Intramuscular Wire Electrodes Are Superior to Surface
Electrodes in the Study of Intrinsic Back Muscles
(Anderson Et Al, 1974, 1977).
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Forward Flexion in Sitting and
Standing Positions Morris Et Al (1962) Found That Flexion-
relaxation Can Occur, but They Felt That inNormal Bending Movements the Back Muscles
Remained Frequently Active.
Spontaneous Electrical Silence of the LumbarMuscles in Extreme Flexion Has Also BeenFound in Subjects, but Only Half of ThemShowed Spontaneous Inactivity of TheirThoracic Muscles in Both Seated and StandingPostures.
Flexion/Relaxation Phenomenon
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Flexion/Relaxation Phenomenon
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This Flexion-relaxation
Phenomena Has Been Validated
by Numerous Studies, and Does
Appear to Be Absent in aPercentage of Low Back Pain
Patients.
During the Valsalva Maneuver
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During the Valsalva Maneuver
With Increased Intrathoracic and
Abdominal Pressure While
Holding a Sandbag of 11.25 Kg,
All Thoracic and a Number ofLumbar Muscles Showed
Activity Instead of ElectricalSilence.
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Extension From the Flexed to the
Upright Posture While Inactivity of the Back Muscles During the
Last Stage of Flexion Can Be Explained in Thatthe Muscles Are No Longer Needed and
Ligaments Are Holding the Vertebral Column,There Is No Explanation of Why These MusclesDo Not Always Become Active ImmediatelyWhen Extension Is Begun.
Instead, There Frequently Are Short "Bursts" ofActivity That Occur (Especially in the LumbarRegion) When the Movement of Extension IsHalf Completed.
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It Therefore Appears That inMost Persons the Lumbar
Transversospinal Muscles Do
Not Initiate Extension From the
Fully Flexed Position.
Lifting Weights With Different
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Lifting Weights With Different
Mechanical Advantages Seemed to
Indicate That in Most InstancesMore Energy Is Used in the Lumbar
and Thoracic Back Muscles When
the Object Lifted Cannot Be Brought
Close to the Line of Gravity of the
Subject. Investigators Also NoticedIncreased Activity of the Back
Muscles When the Center of Gravity
Was Shifted Forward.
Axial Trunk Rotation
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Axial Trunk Rotation In One Study Less Than
Half of the Examined
Subjects Showed theExpected Activity of theTransversospinalMuscles of the ThoracicRegion, Whereas More
Than Half of theSubjects Showed theExpected Activity in theLumbar Region.
This Finding IsSomewhat SurprisingConsidering That Mostof the Actual RotatoryMovement Occurs in the
Thoracic Region.
Paradoxical Activity of the
Deep Muscles Was Found in
Five Subjects at the Thoracicand in Three Persons at the
Lumbar Level.
In the Lumbar Region the
Muscular Activity Seemed
More Often to Support theTheory of Rotatory Function.
On the Other Hand, the
Position of Articular Facets
in Relation to the Direction
of Muscle Pull Casts Doubton the Anatomical Feasibility
of Such a Function.
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Perhaps the Designation of Specific
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Perhaps the Designation of Specific
Function Is Almost Impossible in the
Back, Where We Have a ComplexArrangement of Muscle Bundles
Acting on a Multitude of EquallyComplex Joints. Those Who Insist
on Finding Prime Movers,
Antagonists, and Synergists in theGenuine Musculature of the Back
Will Be Always Disappointed.
In a Wire Electrode Study of
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In a Wire Electrode Study of
Intrinsic Muscles, a Tokyo
Orthopedics Team Was Unable toProvide Validation for Reeducation
Exercises Widely Advocated and
Used in France. Rather Than
Abandon the Exercises, They
Suggested That the TransversospinalMuscles Are Stabilizers and That
This Function Is Important.
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Standing
Continuous Activity of the Back Muscles in theLower Thoracic Region During Standing HasBeen Reported. The Activity of These Muscles
Appears to Depended on Their Relation to theLine of Gravity. The Segments of the VertebralColumn Located Further Posterior to the Line ofGravity Had the Tendency to Fall Forward, a
Movement That Was Counteracted by the BackMuscles. The Thoracic Muscles Showed aGreater Tendency to Remain Active, While theLumbar Muscles Acted With "Bursts" of
Electrical Potentials.
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Some Muscles Apparently
Contract Unnecessarily. TheseContractions Were More Often
Seen in Women and Untrained
Men. Further Confounding Any
Attempt to Seek What Is Normal
for All.
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Asymmetry
There Are Some Differences in Activity of
the Transversospinal Muscles at the Same
Levels. This Asymmetrical Activity Occurred
During Quiet Sitting and Standing but Was
Also Noted With Movements in theSagittal Plane.
Wolf and Basmajian (1980) and Wolf EtAl (1979) A bl d d A l d
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Al. (1979) Assembled and Analyzed
Quantified Data Correlating Normal Back
Movements With the EMG Activity in121 Adult Subjects Who Reported No
History of Low Back Discomfort. EMG
Records Were Obtained From Vertical
Pairs of Surface Electrodes Placed
Bilaterally 3 Cm From the Midline at the
L3-4 and L4-5 Levels. Recordings Were
Made of a Range of Possible Movements
While Standing and Sitting (With the
Pelvis Stabilized).
Differences in Left- and Right-
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Differences in Left and Right
sided Mobility Are Minimal
And, As Expected, Men Showed
a Significantly Greater
Excursion in VertebralSeparation During Complete
Trunk Flexion
Significantly Greater Activity Occurred
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g y y
During Extension From the Flexed
Trunk Position Than Vice Versa forEach Electrode Pairing. For Rotational
Movements in the Standing or Sitting
Postures, Greater Activity Was SeenDuring Rotation Contralateral to the
Location of a Unilaterally Placed
Electrode Pair. The Magnitude of ThisActivity Level Was Not Significantly
Greater for Male or Female Subjects.
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During Stooping or Squatting
Movements, MalesDemonstrated Significantly
Greater Activity Than Females
for Recordings at All Electrode
Placements, Except the Lower
Bilateral Pair.
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All Results in Relation to the Mechanical
Advantage, Center and Line of Gravity, and
the Possible Axis of Movement Confirm the
Idea That the Transversospinal Muscles Act
As Dynamic Ligaments. These Adjust Small
Movements Between Individual Vertebrae,While Movements of the Vertebral Column
Probably Are Performed by Muscles With
Better Leverage and Mechanical Advantage(for Details, See Donisch and Basmajian,
1972).
Normative Data
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Cram and Also Matheson
Have Accumulated
Normative Data for Non-pain Patients but One Must
Be Extremely Careful
Relying on This Data.
Both Studies Used the
Narrow Band Equipment.Wider Frequency Filters Will
Detect More EMG Signal,
and Therefore Readings Will
Vary.
The "Normal Range" Is Very
Broad.
Cram's Data Has Come
Under Scrutiny for Statistical
Error.
Finally Meeker and Others
Have Been Unable to Detect
Differences Between Pain
and Non-pain Controls UsingThis Data.
Most Manufacturers and
Distributors Readily Admit
to the Problem WithNormative Data, but Speak
of Side to Side Asymmetries.
As Noted Above, Not
Enough Is Known About
Complex Acting IntrinsicBack Muscles to Know What
Degree of Asymmetry Is
Normal.
Recently, Some Very ImpressiveSt di S ifi ll Sih d
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Studies, Specifically Sihvonen and
Coworkers From Finland, and Arena and
Co-workers in Augusta Georgia, HaveHad Success in Differentiating Back Pain
Patients From Non-pain Controls. Arena
States That Disk Patients Had the MostSignificant Findings, and Urges for
Diagnostic Categorization of Patients for
Future Studies. It Is Proposed That the
Lack of Diagnostic Criteria Is
Responsible for the Contradictory
Findings of Earlier Investigators.
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Conclusions
"Electromyography Has a Great Deal ofPractical Value in This Area And, Aside
From Some General-but ImportantObservations Recorded Above, MuchRemains to Be Learned by ThisTechnique, Especially About the Fine
Functioning of Various Areas and Depthsof the Intrinsic Muscles of the Back".
Basmajian and Deluca