muscle physiology: the muscle - norris associates

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Journal of Bodywork and Movemen4(4), 225^227# 2000 Harcourt Publishers Ltd

The muscle designationdebate: the experts respond

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Joanne Bullock-Saxton, Donald Murphy, Chris Norris,Carolyn Richardson, PamelaTunnell

M U S C L E P H Y S I O L O G Y

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t Therapies (2000)

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Introduction

Leon Chaitow

A number of the Journal ofBodywork and Movement Therapiesreaders have communicated theirconfusion over the apparentcontradictions in the way di�erentresearchers and clinicians refer tomuscle characterizations. Whenwords such as `postural/phasic' or`stabilizer/mobilizer' are applied toparticular muscles, practical as wellas linguistic di�culties becomeapparent.

It was decided that an exercise inclari®cation should be initiated, andin order to achieve this leadingphysiotherapists, manual medicineand chiropractic researchers andclinicians, were invited to expresstheir understanding of the issues.The objective is quite simply anattempt to remove confusion.

Questions were posed by theeditor, in consultation with associateeditor Craig Liebenson, to whichbrief, succinct, responses wererequested.

It was stressed that, whereverpossible, research validation shouldbe quoted with the answers, howeverpersonal opinions based on clinicalexperience would also be welcome.As well as answering the questions,

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YWORK AND MOVEMENT THERAPIES

each respondent was o�ered theopportunity to make a `positionstatement'.

It is hoped that out of this exercisea clearer picture will emerge ofcurrent thinking on this topic, andthat commissioned papers will takethe process further.

The editor wishes to thank allthose who participated in thisendeavour, in which the onlywinners will be currently confusedpractitioners and therapists, andultimately their patients.

The questions posed were asfollows:

1. It has been suggested that`postural' muscles tend towardsoveruse and eventual shortening,whereas phasic muscles tendtowards disuse and weakness.

. Jull G, Janda V 1987 Musclesand motor control in low backpain: Assessment management.In: Twomey L (ed) PhysicalTherapy of the Low Back.Churchill Livingstone, NewYork

. Bullock-Saxton J, Janda V,Bullock M 1993 Re¯exactivation of gluteal muscles inwalking. Spine 18: 704

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Fig. 1 The major postural muscles of the anterior aspect of the body.

Fig. 2 The major postural muscles of the posterior aspect of the body.

Bullock-Saxton et al.

Expand on why you consider thissuggested model valid, and if notwhy not?

2. It has been suggested thatdynamic phasic muscles whichtend to weakness contain apredominance of slow twitchType 11 ®bres and that posturalmuscles which tend to shorteningcontain a predominance of Type1 ®bres.

. Hu J 1992 Stimulation ofcraniofacial muscle a�erentsinducing prolonged facilitatorye�ects in trigeminalnociception brainstemneurons. Pain 48: 53

. Liebenson C 1996Rehabilitation of the spine.Williams & Wilkins

Please comment.3. The designation of muscles as

stabilizers (deep, slow twitch)with a propensity to weaken andlengthen; and mobilizers(super®cial, with propensity toshorten and tighten) is a morerecent characterization. Furthercategorizations occur within thismodel including `primary'stabilizers (unable to providesigni®cant joint movement) and`secondary' stabilizers (able tostabilize and move joints) and`tertiary' stabilizers (which can attimes provide defensive rigidity).

. Richardson C, Jull G,Toppenberg R, Comeford M1992 Techniques for activelumbar stabilisation for spinalprotection. Australian Journalof Physiotherapy 38: 105±112

. Norris C 1999 FunctionalLoad Abdominal TrainingJournal of Bodywork andMovement Therapies 3:150±158

Expand on why you consider thissuggested model valid, and if notwhy not?

4. For the most part stabilizermuscles appear to be similar to

226

JOURNAL OF BODYWORK AND MOVEMENT THERAPIES OCTOBER 2000

Fig. 3 The layer syndrome. (reproduced for Jull and Janda 1987).

. .

Jo4(#

Jo(M

Se

U

A

Themuscle designation debate: the experts respond

phasic muscles, while mobilizermuscles are similar to posturalmuscles. However, the quadratuslumborum muscle appears to be

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urnal of Bodywork and Movement Therapies (2000)4), 227^2292000 Harcourt Publishers Ltd

anne Bullock-Saxton PhD,MAppPhty St

anips),BPhty(hons)

nior Lecturer, Department of Physiotherapy, The

niversity of Queensland, St. Lucia, 4072, QLD,

ustralia

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the source of confusion. How doyou classfy this?

Similarly, can you comment onhow you classify the

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WORK AND MOVEMENT THERAPIES

. multi®dus,

. transverse abdominus,

. rectus abdominus muscles.

5. Comment on where (if at all) yousee ®bre type of muscles as beinga feature of your thinkingregarding their characterizationas phasic, postural, stabilizer,mobilizer, etc?

6. Do you have a di�erent way ofdesignating or characterizingmuscles that is of practicalclinical value to you?

Note: The responses to thesequestions are listed in alphabeticalorder. Most of the respondingresearchers and clinicians havefollowed the question sequence inproviding their insights, howeverDr Bullock-Saxton chose insteadto provide a position statementwhich took a global view of theissues raised.

Response from Joanne Bullock-Saxton

Position statement öa global view

Thank you for the opportunity torespond to the questions that youpose for comment among cliniciansand researchers world wide.Confusion does arise with the use ofdi�ering nomenclature that is in thiscase, predominantly describingdi�erences in activation pattern ofvarious muscles. All of the questionshave a common theme, and for thisreason I have tried to give a

response to the questions from aglobal perspective rather than eachquestion separately.

The nomenclature devised todescribe muscle functions over thelast decades have attempted toclassify general movement patterns,as well as responses observed tooccur associated with injury/disease.Most observation until recently hasbeen limited in this regard toinferences about deep musclesthrough observation ofbiomechanics and assessment withEMG. More recently studies using®ne wire EMG, MRI andDiagnostic Ultrasound haveprovided some detail about thefunction of more deep muscles.However, the reader of theresearch literature must keep inmind that all of these methods of

measurement of muscle functionhave limitations.

A reminder of some of thecommon denominators related toour function seems essential at theoutset of consideration of thequestions raised in this debate. Allhuman bodies have similar musclealignment about joints of relativelysimilar structure and range ofmotion. Most human bodies will beinvolved in activities of lying,sitting, standing and walking. Theseactivities are all performed againstthe constant force of gravity. It isknown that the force of gravitycombined with movements of dailyliving stimulates peripheralreceptors, that send neural messagesto the spinal cord and then tosubcortical and cortical nuclei. Themotor response to the sensory

OCTOBER 2000


stimulus is regulated according tothe needs of the movement pattern,on the whole the majority of signalsare inhibited.

This is of course an extremelysimplistic illustration of motorcontrol, but the overview does servethe purpose of illustrating that weare designed to move in anenvironment that imposes upon us aforce. Naturally there will be somemuscles, through their attachmentto our skeletal system and due to thecharacteristics of our articularsystem that will work more oftenagainst this force of gravity. Thissituation will in¯uence the quantityof sensory information from themuscles and the periarticular tissues,and thus the information that passesthrough the spinal cord to the CNSfor interpretation and action. As anexample, our upper limb is arrangedbiomechanically to enable us to eat,groom and dress ourselves, ourscapular elevators and protractors,shoulder ¯exors and internalrotators, elbow ¯exors and wrist¯exors are all more readily activatedand also, all work against gravity.These muscles are alsopredominantly activated in painwithdrawal responses. In the lowerlimb, muscles that work against theforce or gravity also correspondwith those that are activated in apain withdrawal response andinclude pelvic elevators (pelvichitchers, such as QL), hip adductors,hip ¯exors, knee ¯exors and ankleplantar ¯exors. Essentially however,I would hesitate to call these musclesany name, although they are whatJanda would have termed `postural'muscles. The terminology obviouslyin¯uenced by the nature of ouranatomy and our movement withinour environment.

Of relevance to this particulardebate is the genesis and subsequentresearch development of clinicalobservations ®rst made by Janda inthe 1960's. Janda (1964, 1977, 1978)described an observation of

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dysfunction in muscles in chronicpain patients that was similar topatterns of `over' and `under'activity seen in subjects withcerebral palsy (CP). Those with CPdemonstrating patterns of muscleactivity re¯ecting a loss of centralinhibition to the constant peripherala�erent information of the force ofgravity generated by patterns ofdaily living. Janda (1978, 1984) hasproposed that these patternedresponses can occur not only in thecase of cerebral accidents/dysfunction but also in the casewhere there is an altered degree ofactivity from peripheral sensoryreceptors or an alteration in thestimulation threshold of spinal cordcells. Peripheral injury,in¯ammation, altered jointbiomechanics are a few exampleswhere peripheral a�erentinformation may alter. Recentliterature studying the e�ect ofperipheral pain stimuli (Coderre &Melzack 1987; Cook et al. 1987;Grubb et al. 1993; Schaible & Grubb1993; Woolf 1983) has supportedthese claims. These researchersdescribe how pain stimuli arecapable of altering the sensitivity tocentral perception of pain and othera�erent stimuli as well as alteringthe e�erent response not only at onesegmental level, but to many levelsboth ipsilateral and contralateral tothe source of the stimuli.

What Janda has really remindedthe clinician is that anunderstanding of the de®cit in theneural system is essential fortreatment. Treatment of the musclepattern response without thisperspective can be misdirected andfutile. E�ectively the muscles are there¯ection of either some peripheralneural change or some centralneural change. Treatment will onlybe e�ective if directed at the correctneural disruption. Again recentresearch is tending to con®rm theseinitial statements. Panjabi (1992) hasemphasized the importance of the

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triad of the three musculoskeletalsystems of (a) control subsystem(peripheral and central neuralcontrol), (b) active subsystem(muscles) and (c) passive subsystem(articulating surfaces andperiarticular soft tissues),functioning well to provide adequatespinal stability. Richardson andcolleagues also strongly emphasisethe need to address neural controlissues related to motor control andmuscle coordination whenrehabilitating patients with chroniclow back pain (Richardson et al.1998). Thus the emphasis is on theneural dysfunction that is re¯ectedin a muscle, rather than in themuscle itself.

REFERENCES

Coderre T, Melzack R 1987 Cutaneous

hyperalgesia: contributions of the

peripheral and central nervous systems to

the increase in pain sensitivity after

injury. Brain research 404: 95±106

Cook A, Woolf C, Wall P, McMahon S 1987

Dynamic receptive ®eld plasticity in

rat spinal cord dorsal horn following

C-primary a�erent input. Nature 325:

151±153

Grubb B, Stiller R, Schaible H-G 1993

Dynamic changes in the receptive ®eld

properties of spinal cord neurons with

ankle input in rats with chronic unilateral

in¯ammation in the ankle region.

Experimental Brain Research 92:

441±452

Janda V 1964 Movement patterns in the

pelvid and the hip region with special

reference to pathogenesis of

vertebrogenic disturbances, Habilitation

Thesis, Charles University Praha, Czech

Republic

Janda V 1969 Postural and Phasic Muscles in

the Pathogenesis of Low Back Pain.

Proceedings of the XI Congress of the

ISRD, Dublin 1969, 553±554

Janda the 1977 Comparison of Spastic

Syndromes of Cerebral Origin with the

Distribution of Muscular Tightness in

Postural Defects. Rehabilitacia Ð Suppl.

14±15, 87±88. V. International

Symposium on Rehabilitation in

Neurology, Prague

Janda V 1978 Muscles motor regulation and

back problems: In: Korr IM (ed). The

Neurologic Mechanisms in Manipulative

Therapy. Plenum Press, New York

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Janda V 1980 Muscles as a Pathogenic Factor

in Back Pain. Proceedings of the IVth

International Federation of Orthopaedic

Manipulative Therapists. Christ Church,

New Zealand

Janda V 1986 Muscle weakness and inhibition

(pseudoparesis) in back pain syndromes.

In: Grieve G (ed). Modern Manual

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Journal of Bodywork and Movement Therapies (2000)4(4), 229^232# 2000 Harcourt Publishers Ltd

Donald R. Murphy DC,DACAN

Rhode Island Spine Center, Providence, RI

E-mail: [email protected]

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Therapy of the Vertebral Column.

Churchill Livingstone, Melbourne

Panjabi M 1992 The stabilizing system of the

spine. Part I Function, dysfunction

adaptation and enhancement. Journal of

Spinal Disorders 5: 383±389

Richardson C, Jull G, Hodges P, Hides J 1998

Therapeutic exercise for spinal segmental

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stabilization in low back pain. Sydney,

Harcourt Publishers

Schaible H-G, Grubb B 1993 A�erent and

spinal mechanisms of joint pain. Pain 55:

5±54

Woolf C 1983 Evidence for a central

component of post-injury pain

hypersensitivity. Nature 306: 686±688

Response from Donald R. Murphy

Position statement

It is important to be as accurate aspossible when describing thefunction and dysfunction ofmuscles. This importance is for twoprimary reasons. First,interpractitioner andinterdisciplinary communication isenhanced when all concerned canhave a common language in whichthey are communicating, even ifthere is not always (goodnessknows!) complete aggreementregarding the speci®cs of the topicdiscussed. Second, and moreimportantly, it is our conceptualunderstanding of function anddysfunction that drives the clinicaldecisions that we make in practice.Thus, the accuracy or inaccuracy ofour concepts will determine thesuccess or failure of ourmanagement approach. So I see thisexercise not merely as one ofsemantics, but rather an importantlook at some of the essentialconcepts under which we work intreating patients withneuromusculoskeletal painsyndromes.

1. It has been suggested thatpostural muscles tend towardsoveruse and eventualshortening, whereas phasicmuscles tend towards disuseand weakness. Expand on whyyou consider this suggestedmodel valid, and if not why not?

When Janda ®rst suggested thedesignation of muscles intocategories of `postural' (tonic) and`phasic' classi®cations, it served as auseful way of conceptualizingseveral of his clinical theories. Themost important of these theories wasbased on his clinical observation,and laboratory measurement (Janda1978) of relative tightness andinhibition (this is the word that Iprefer rather than weakness Ð moreon this later) of certain muscles. Itseemed that there were certainmuscles that tended to easily becometight and hyperactive, and certainmuscles that tended to becomeinhibited and underactive. Inlooking further at these muscles, itappeared that those that tendedtoward tightness had certaincommon characteristics andthose that tended towardinhibition had certain commoncharacteristics.

I do not know that there is aprecise distinction between `tonic'and `phasic' muscles, and whether acertain category of muscles tendtoward overuse, while others tend

toward underuse. To my knowledge,there is no data on over- or underuseof certain muscles. It seems to methat the imbalance of activity inmuscles relates more to the nervoussystem's selective activation (or lackthereof ) of certain muscles, thanproperties of the muscles themselves.In other words, if a muscle becomeshypertonic (increased muscle tone)or hypotonic (decreased muscletone), this occurs as a result ofcertain neurological eventsthat occur, not because themuscle is `tonic' or `phasic'(Johansson & Sojka 1990, Stokes &Young 1989).

2. It has been suggested thatdynamic phasic muscles whichtend to weakness contain apredominence of slow twitchType11 ¢bres and that posturalmuscles which tend toshortening contain apredominence of Type1 ¢bres

The subject of ®bre type in variousmuscles is a di�cult one, as there is agreat deal of individual variation,with widely disparate percentages of`slow twitch' and `fast twitch' ®bresin di�erent people (Weber et al.1993). Probably the most thoroughreview of this topic has been that ofNg et al. (1998), who found thatthere is a general trend toward moreslow twitch ®bres in back muscles

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(53±73%) but that there is not agreat preponderance of this type of®bre compared to type II.

Perhaps more important thanclarifying the di�erence betweentonic and phasic muscles and ®bretypes is clarifying the di�erencebetween `inhibited' and `weak'. Agreat deal of confusion exists hereand proper understanding of theseconcepts is critical in order forcorrect treatment decisions to bemade. The term `weak' refers to theability of a certain muscle togenerate torque production. Thequality being addressed with thisword is `strength'. But, in myexperience, lack of proper strength isnot commonly an important issue inthe clinical syndromes with whichpatients consult every day. Thisobservation is supported by severalstudies that have shown thatstrength is not a prominent factor ininitial onset of low back pain, or inrisk for chronicity (Hunter et al.1998; Hildebrandt et al. 1997;Leamon 1994; Frymoyer 1992;Adams et al. 1987). However, it iscommon to ®nd that inhibition ofcertain muscles, especially musclesthat have an important stabilizationrole, in patients with spinalcomplaints (Aleksiev et al. 1996;Hodes & Richardson 1996;Radebold et al. 2000; Solomonow etal. 1999). `Inhibition' refers to theability of a muscle to react tostimuli. These stimuli may beexternal, in the form of aperturbation that has the potentialto cause injury, and to which themuscle must respond with protectivemuscle activity, or internal, in theform of a centrally orderedmovement pattern (Murphy 2000a).So it is important to realize that,while most muscles in patients withspinal complaints will have su�cientstrength to perform their role inmovement and stability, if thecentral nervous system is notproperly activating them at the rightmoment, to the correct magnitude

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and in harmony with the othermuscles involved in the activity,dysfunction and microtrauma mayresult. From a clinical standpoint,this is far more important than`weakness'.

3. The designation of musclesas stabilizers (deep, slowtwitch) with a propensity toweaken and lengthen; andmobilizers (super¢cial, withpropensity to shorten andtighten) is a more recentcharacterization. Furthercategorizations occur withinthis model including `primary'stabilizers (unable to providesigni¢cant joint movement) and`secondary' stabilizers (able tostabilize and move joints) and`tertiary' stabilizers (which canat times provide defensiverigidity). Expand on why youconsider this suggested modelvalid, and if not why not?

I think that the classi®cation schemeof stabilizers/mobilizers is good, asit brings us somewhat closer to thereal clinical and functionalproperties of each muscle. However,the classi®cation scheme of primary/secondary/tertiary stabilizers ismuch better, as it recognizes thatvirtually all muscles are capable ofproviding a stabilizing function,although some are better equippedthan others. For example, thelumbar erector spinae muscles areconsidered relatively poor stabilizersof the spine (Richardson & Jull1995), but are capable, at times, ofco-contracting with other muscles inenhancing, if not solely providing,stability (Cholewicki et al. 1995). Onthe other hand, the multi®dismuscles, while being excellentstabilizers (Wilke et al. 1995),produce little or no joint movement.

4. For the most part stabilizermuscles are similar to phasic

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while mobilizer muscles aresimilar to postural. However, thequadratus lumborummuscleappears to be the source ofconfusion. How do you classifythis muscle? Similarly, can youcomment on how you classifythe

. multi¢dus,


. rectus abdominusmuscles.

Little is known about the quadratuslumborum (QL). McGill et al.(1996) recently demonstrated thestability function of the QL, whenthey measured the EMG activity inthis muscles while progressivelyheavier weights were handled bynormal subjects. They found thatthe activity in the QL steadilyincreased as more weight washandled. Importantly, no lateralbending of the trunk took place, sothe activity seen was purely for thepurpose of maintaining stability ofthe lumbar spine. The activitydevelopment in the QL was greaterthan that in the rectus abdominis,internal oblique, external obliqueand erector spinae. They did notmeasure the transverse abdominis ormulti®dis. Certainly from ananatomical standpoint, the QLappears to be an e�cient stabilizer,as its attachments are fairly close tothe center of rotation of the spine.

The question remains, to whatextent is the QL active in mobilizingthe lumbar spine or pelvis, i.e. whatis its capacity as a `mobilizer'?Classically, the QL is thought tocontribute to lateral ¯exion of thelumbar spine, hip hiking, unilateralstance and hip abduction(Lehmkuhl et al. 1983). To myknowledge, little work has beendone to accurately determine theextent to which it contributes tothese movements. I would classify itas secondary stabilizer.

I think it is pretty clear that boththe multi®dis and the transverse

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abdominis should be consideredprimary stabilizers. That is, theyprovide excellent stability, but donot, in and of themselves, producejoint movement (Hodges 1999). Therectus abdominis should beconsidered a tertiary stabilizer. It isnot an e�ective primary orsecondary stabilizer, as it is placedtoo far from the center of rotation ofthe spine. However it, like theerector spinae, is capable ofgenerating tension su�cient to assistin stabilization when it co-contractswith the primary and secondarystabilizers. One must be careful,however, when training a patient forstability, to avoid excessiveactivation of the rectus abdominis,as this can cause inhibition of thetransverse abdominis (O'Sullivanet al. 1998).

5. Please comment on where(if at all) you see ¢bre type asbeing a feature of your thinkingregarding suchcharacterizations?

As I suggested before, I do not feelthat ®bre type is essential in thedesignation of a muscle as primary,secondary or tertiary stabilizer. Theprimary reason for this is that astabilizer muscle functions to bothprovide ongoing stability on acontinuous basis over a period oftime and to respond toperturbations that have the potentialto cause injury. Continuous activityis provided by the slow twitch ®bresin the muscle and response toperturbation is provided by the fasttwitch ®bres. So, a balance of bothtypes of ®bres is necessary forproper stability. Much moreimportant is the muscle's anatomicallocation, particularly the proximityof the belly of the muscle to thecenter of rotation of the joint(s) itsjob it is to protect. Those musclesthat maintain a position relativelyclose to the center of rotation, suchas the transverse abdominis,

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multi®dis and deep cervical ¯exorsplay a more prominent role instability. Those whose lever arm isfarther from the center of rotation,such as the rectus abdominis orsternocleidomastoid, play a lesserrole. Also, the shorter muscles, suchas the suboccipitals, tend to betterstabilizers than longer muscles, suchas the erector spinae.

6. Do you have a di¡erent wayof designating or characterizingmuscles that is of practicalclinical value to you?

I think that the primary, secondaryand tertiary stabilizer designation isa good one for clinically classifyingmuscles with regard to stabilization.I use a variation of the originalJanda designations with regard tomuscle that tend to becomeinhibited, hypertonic and tight(Murphy 2000a). First, as I statedbefore, I think it is essential that wemake a clear distinction between`weak' and `inhibited'. Also, I thinkit is important to make thedistinction between `tight' and`hypertonic'. The reason for this isthat each muscle condition requiresa di�erent treatment approach.Hypertonicity is de®ned as, literally,too much muscle tone. Muscle toneinvolves two characteristics of amuscle: (1) the degree of resistanceto stretch and (2) the readiness withwhich the nervous system activatesthe muscle in response to stimuli(Davido� 1993, Basmajian &DeLuca 1985). Therefore, byde®nition, hypertonicity is anabnormal increase in the resistanceto stretch of a muscle and anabnormal increase in the readinesswith which the nervous systemactivates the muscle in response tostimuli. As was discussed previouslywith regard to inhibition, thesestimuli can be peripheral, as in anexternal perturbation, or internal, asin a centrally ordered movementpattern. Notice that in this

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de®nition, there is nothing regardingresting length of the muscle. This isbecause resting length has nothingto do with muscle tone. However,when muscle tightness exists, there isboth an increase in muscle tone anda decrease in the resting length of themuscle, presumably as a result ofshortening of the connective tissueelements of the muscle (Janda 1994).In my clinical experience, when truemuscle tightness is present, adi�erent type of treatment (i.e.,postfacilitation or Active Release[Leahy & Schneider 2000]) isrequired, as compared tohypertonicity, in which casepostisometric relaxation is best.

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Adams MA, Mannion AF, Dolan P 1999

Personal risk factors for ®rst-time low

back pain. Spine 24: 2497±2505

Aleksiev A, Pope MH, Hooper DM 1996

Pelvic unlevelness in chronic low back

pain patients Ð biomechanics and EMG

time-frequency analyses. European

Journal of Physical Medicine and

Rehabilitation 6: 3±16

Basmajian JV, DeLuca CJ 1985 Muscles

Alive: Their Functions Revealed by

Electromyography. Williams and

Wilkens, Baltimore

Cholewicki J, Panjabi M, Khachatryan A

1997 Stabilizing function of trunk ¯exor-

extensor muscles around a neutral spine

posture. Spine 22: 2207±2212

Davido� RA 1993 Skeletal muscle tone and

the misunderstood stretch re¯ex.

Neurology 1992; 42: 951±963

Frymoyer JW 1992 Predicting disability from

low back pain. Clin Orthop Rel Res 279:

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1997 Prediction of success from a

multidisciplinary treatment program for

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Hodges PW, Richardson CA 1996

Ine�cient muscular stabilization of the

lumbar spine associated with low back

pain: a motor control evaluation of

transversus abdominis. Spine 21:

2640±2650

Hodges PW 1999 Is there a role for

transversus abdominis in lumbo-pelvic

stability? Manual Therapy 4: 74±86

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Hunter SJ, Shaha S, Flint D, Tracy DM

1998 Predicting return to work: a

long-term follow-up study of railroad

workers after low back injuries. Spine 23:

2319±2327

Janda V 1978 Muscles, central nervous motor

regulation, and back problems. In: Korr

IM (ed). The Neurobiologic Mechanisms

of Manipulative Therapy. Plenum Press,

New York

Janda V 1991 Muscle spasm Ð a proposed

procedure for di�erential diagnosis.

Manual Medicine 6: 136±139

Johansson H, Sojka P 1990

Pathophysiological mechanisms involved

in genesis and spread of muscular tension

in occupational muscles pain and in

chronic musculoskeletal pain syndromes:

a hypothesis. Medical Hypotheses; 35:

196±203

Leahy PM, Schneider JM 2000 Active release

techniques for the cervical spine. In:

Murphy DR (ed). Conservative

Management of Cervical Spine

Syndromes. McGraw-Hill, New York

Leamon TB 1994 Research to reality: a

critical review of the validity of various

criteria for the prevention of

occupationally induced low back pain

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Chris Norris MCSP

20 Eastway, Sale, Cheshire M33 4DX, UK.

E-mail: [email protected]

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disability. Ergonomics 37: 1959±1974

Lehmkuhl LD, Smith LK 1983 Brunnstrom's

Clinical Kinesiology, 4th Ed. FA Davis,

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McGill S, Juker D, Kropf P 1996

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activity of quadratus lumborum during a

wide variety of tasks. Clinical Biomechics

11: 170±172

Murphy DR 2000 Dysfunction in the cervical

spine. In: Murphy DR (ed). Conservative

Management of Cervical Spine

Syndromes. McGraw-Hill, New York

Murphy DR 2000 Examination and treatment

of muscle and soft tissue dysfunction of

the cervical spine. In: Murphy DR (ed).

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Parnianpour M 1998 Relationship

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Altered abdominal muscle recruitment in

patients with chronic back pain following

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a speci®c exercise intervention.

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Ð pain control. What exercises would

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Harris M 1999 Biomechanics of increased

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muscular stabilization. Spine 24:

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re¯ex inhibition to arthrogenous muscle

weakness. Clinical Science 1989; 67: 7±14

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Muntener M 1993 Duration of pain and

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Response from Chris Norris

Position statement

Categorization of muscle is useful asa clinical guide, but is not an exactscience. By categorizing muscles intostabilizor and mobilizor groups theclinician can focus attention on thetype of management likely to berequired. Stabilizor muscles arelikely to be poorly recruited, lax inappearance, show an inability toperform inner range contractionsover time, and as a result alter bodyalignment by failing to provide a

stable base for other muscles towork from. Mobilizor muscles onthe other hand are likely to the tight,and show preferential recruitment insynergistic activities. These muscleswill tend to dominate movementsand may alter posture by restrictingmovement and preventing optimalsegmental alignment. Thecombination of muscle laxity andpoor holding ability on the one handwith muscle tightness anddominance on the other hand withinan antagonistic muscle pairing willalter the equilibrium point of thejoint, tending to pull the jointtowards the tight muscle. Aninability to move actively throughfull range due to a combination oftightness with poor inner rangecontrol will change the nature of a

movement entirely. Although thesechanges may be subtle, over timestress accumulation may givechronic pathologic changes withinsoft tissue and possible degenerativechanges within bone.

Any relatively simplisticcategorization of muscle is fraughtwith problems. The danger withmuscle imbalance categorization isthat practitioners will expect setchanges to occur and fail toadequately assess a patient. Whenthis occurs, important deviationsfrom the imbalanced norm can bemissed and treatment outcomes willbe impaired. Although muscleimbalance categorization canusefully assist the astutepractitioner, they are not cast instone. Assessment will still be

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required but can be re®ned to revealthe subtleties of muscle reaction toaltered use and pathology. If amuscle has poor inner rangeholding, this must be enhanced, anda variety of protocols exist to dothis. If a muscle is tight, a number ofprocedures are available to lengthenit. Once muscle balance has beenrestored, habitual changes inposture (local and general, staticand dynamic) must be addressed.Only then can we truly say thatthe patient has moved closer tooptimal alignment and reduced animportant risk factor formusculoskeletal pain.

1. It has been suggested thatpostural muscles, whenstressed through overuse tendto shorten, whereas phasicmuscles tend towards disuseand weakness. Expand on whyyou consider this suggestedmodel valid, and if not why not?

The terms postural and phasic usedby Jull and Janda (1987) can bemisleading. In their categorization,the hamstring muscles are placed inthe postural grouping while thegluteals are placed in the phasicgrouping. The reaction described forthese muscles is that the posturalgroup (represented by thehamstrings in this case) tend totighten, are biarticular, have a lowerirritability threshold and a tendencyto develop trigger points. This typeof action would suggest a phasic (asopposed to tonic) response, and istypical of a muscle used to developpower and speed in sport forexample, a task carried out by thehamstrings. The so called `phasicgroup' is said to lengthen, weakenand be uniarticular, a descriptionperhaps better suited to thecharacteristics of a muscle used forpostural holding. The description ofthe muscle responses described byJull and Janda (1987) is accurate,but the terms postural and phasic do

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not seem to adequately describe thegroupings.

2. It has been suggested thatdynamic phasic muscles whichtend to weakness contain apredominence of slowtwitchType11 ¢bres andthat postural muscleswhich tend to shorteningcontain a predominence of Type1 ¢bres

In addition to basic type I (slowtwitch/slow oxidative/SO) and typeII (fast twitch/fast glycolytic/FG)muscle ®bres, histochemical staining(myosin ATPase) reveals severalfurther ®bre subtypes, includingtype IIA (fast-oxydative-glycolyticor FOG) (Staron et al. 1983).Adaptation of muscle due todecreased usage has mostly beenstudied by limb immobilizationexperiments, usually using rathindlimb muscle. The predominantdecline appears to be in the type I(SO) ®bres with a correspondingincrease in the proportion of IIA(FOG) ®bres (Oishi et al. 1992). Oneexplanation for this change is thatthe type I ®bres are most a�ected byimmobilization because it is these®bres whose activity is reduced themost. Type I ®bres are normallyactive at low tension levels roughly20±30% maximum voluntarycontraction (MVC) (Sale 1992) thetype of activity used in daily living.Larger diameter ®bres (IIA and IIB)are recruited at much higher levels(up to 90% MVC) during strengthtraining activities, and theseactivities are obviously not used asfrequently. Greater reduction in sizeand loss of number is seen in type I®bres showing selective atrophy.The uniarticular muscles showing an`antigravity' function with apredominance of type I ®bres suchas the soleus and vastus medialishave both been shown to wastemore during immobilization. Nextin order of atrophy are the slow

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antigravity muscles, which covermultiple joints such as the erectorspinae. The muscles with apredominance of type II ®bres showthe least wastage in ®bres (Appell1990; Lieber 1992).

3. The designation of musclesas stabilizers (deep, slowtwitch) with a propensity toweaken and lengthen; andmobilizers (super¢cial, withpropensity to shorten andtighten) is a more recentcharacterization. Furthercatagorizations occur withinthis model including `primary'stabilizers (unable to providesigni¢cant joint movement) and`secondary' stabilizers (able tostabilize and move joints) and`tertiary' stabilizers (which canat times provide defensiverigidity). Expand on why youconsider this suggested modelvalid, and if not why not?

The designation of muscles intostabilizors and mobilizors wouldseem to more accurately describeboth the function of the muscles andthe muscle reaction seen clinically.Further division into primary andsecondary stabilizors usefullydi�erentiates between those muscleswhich can or cannot contributesigni®cantly to joint movement.Certain muscles, for example theMulti®dus (Hides et al. 1994) andVastus medialis (Stokes and Young1984) have been shown to respondby inhibition (rather than disuseatrophy) to swelling and pain. Thesemuscles produce little torque but area�ected by subtle changes in jointalignment.

4. For the most part stabilizermuscles are similar to phasicwhile mobilizer muscles aresimilar to postural. However, thequadratus lumborummuscleappears to be the source of

OCTOBER 2000


confusion. How do you classifythis muscle? Similarly, can youcomment on how you classifythe

. multi¢dus,



The quadratus lumborum has beenshown to be signi®cant as astabilizor in lumbar spinemovements (McGill 1996) whiletightening has also been described(Janda 1983). It seems likely that themuscle may act functionally inmedial and lateral portions with themedial portion being more active asa stabilizor of the lumbar spine andthe lateral more active as amobilizor. Such sub-division is seenin a number of other muscles forexample the gluteus medius wherethe posterior ®bres are moreposturally involved (Jull 1994) theinternal oblique where the posterior®bres attaching to the lateral rapheare considered stabilisors (Bergmark1989) the external oblique where thelateral ®bres work during ¯exion inparallel with the rectus abdominis(Kendal et al. 1993). The multi®dusmay be classi®ed as a stabilizortogether with the transversusabdominis as both lie close(r) to theaxis of rotation of the spine than doother muscles in the spinal orabdominal groups respectively. Therectus abdominis may be classi®edas a mobilizor as it is moresuper®cial (and therefore furtherfrom the axis of rotation). Inaddition, the rectus showspreferential recruitment, tending todominate abdominal muscle actions.Clinically when this happens,patients ®nd recruiting thetransversus abdominis moredi�cult.

5. Please comment on where(if at all) you see ¢bre type asbeing a feature of your thinking

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regarding suchcharacterizations?

Although ®bre type has been used asone factor to categorize muscles, itsuse clinically is limited as an invasivetechnique is required. It is thereforethe functional characteristics of themuscle that is of more use to theclinician. Stabilizing muscles show atendency to laxity and an inability tomaintain a contraction (endurance)at full inner range. Mobilizingmuscles show a tendency totightness through increased restingtone. The increased resting tone ofthe muscle leads to or co-exists withan inclination for preferentialrecruitment where the tight muscletends to dominate a movement. Thestabilizing muscle in parallel shows atendency to reduced recruitment orinhibition as a result of pain or jointdistension.


A further categorization of muscleshas been used by Bergmark (1989)and expanded by Richardson et al.(1999). They have used thenomenclature of local (central) andglobal (guy rope) muscles the laterbeing compared to the ropes holdingthe mast of a ship. The centralmuscles are those which are deep, orhave deep portions attaching to thelumbar spine. These muscles areseen as capable of controlling thesti�ness (resistance to bending) ofthe spine and of in¯uencingintervertebral alignment. The globalcategory includes larger moresuper®cial muscles. Global musclesinclude the anterior portion of theinternal oblique, the externaloblique, the rectus abdominis, thelateral ®bres of the quadratuslumborum and the more lateralportions of the erector spine(Bogduk 1991). The local

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categorization includes themulti®dus, intertrasversarii,interspinales, transversusabdominis, the posterior portion ofthe internal oblique, the medial®bres of quadratus lumborum andthe more central portion of theerector spinae. The global systemmoves the lumbar spine, but alsobalances/accommodates the forcesimposed by an object acting on thespine.

REFERENCES

Appell HJ 1990 Muscular atrophy following

immobilization: a review. Sports

Medicine 10, 42

Bogduk N, Twomey L 1991 Clinical anatomy

of the lumbar spine (2nd ed). Churchill

Livingstone, Edinburgh

Bergmark A 1989 Stability of the lumbar

spine. A study in mechanical engineering.

Acta Orthopaedica scandinavica 230

(suppl): 20±24

Hides JA, Stokes MJ, Saide M, Jull GA,

Cooper DH 1994 Evidence of lumbar

multi®dus muscle wasting ipsilateral to

symptoms in patients with acute/sub

acute low back pain. Spine 19: 165±172

Janda V 1983 Muscle function testing.

Butterworth, London

Jull G 1994 Active stabilisation of the trunk.

Course notes, Edinburgh

Jull G, Janda V 1987 Muscles and motor

control in low back pain: assessment and

management. In: Twomey L (ed).

Physical Therapy of the Low Back.

Churchill Livingstone, New York

Kendall FP, McCreary EK, Provance PG

1993 Muscles. Testing and function (4th

ed). Williams and Wilkins, Baltimore

Lieber RL 1992 Skeletal muscle structure and

function. Williams and Wilkins,

Baltimore

McGill SM, Juker D, Kropf P 1996



wide variety of tasks. Clinical

Biomechanics 11: 170±172

Oishi Y, Ishihara A, Katsuta S 1992 Muscle

®bre number following hindlimb

immobilization. Acta Physiologica

Scandinavica 146: 281±282



stabilisation in low back pain.

Edinburgh, Churchill Livingstone

Sale DG 1992 Neural adaptation to strength

training. In: Komi PV (ed). Strength and

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Power in Sports, IOC Medical

Publication. Blackwell Scienti®c, Oxford

Staron RS, Hikida RS, Hagerman FC 1983

Re-evaluation of human muscle fast

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Carolyn Richardson PhD

Department of Physiotherapy The University of

Queensland, Brisbane Qld 4072, Australia.

E-mail: crichardson@physio. therapies.uq.edu.au

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twitch subtypes: evidence for a

continuum. Histochemistry

78: 33±39

235

WORK AND MOVEMENT THERAPIE

Stokes M, Young A 1984 The contribution of

re¯ex inhibition to arthrogenous muscle

weakness. Clinical Science 67: 7±14

Response from Carolyn Richardson

Position statement

For many years traditional exercisetherapy was mainly focussed onbuilding strength or endurance ofwhole muscle groups, e.g. rotatorsof the trunk, extensors of the knee,internal rotators of the shoulder.Those involved in rehabilitativeexercise gradually realized thatpeople with injury not only neededgeneral strength and endurance ofwhole muscle groups to perform anactivity, e.g. lifting a load, but alsoneeded more speci®cally directedexercise.

More speci®cally exercise regimeswere necessary to take into accountthat some individual muscles of asynergistic group:

1. have distinct and di�erentindividual functions,

2. react in di�erent ways to injuryof the associated joint (re¯exinhibition and excitation),

3. react in di�erent ways to lackof use or lack of gravitationalload,

4. react in di�erent ways tospeci®c patterns of use (e.g.ballistic, repetitive activity).

In each of the above it can beeasily predicted that individualmuscles would fall consistently intobasically two groups.

Group A

1. more linked with jointstabilization,

2. more likely to undergo re¯exinhibition with injury toassociated joint,

3. more likely to atrophy quicklydue to lack of use or lack ofgravitational load,

4. more likely to decrease activityand change their functionwhen exposed to ballisticrepetitive exercise.

Group B

1. more linked with e�cientmovement of joints,

2. more likely to undergo re¯exexcitation with injury toassociated joint,

3. not prone to atrophy quicklydue to lack of use or lack ofgravitational load,

4. more likely to become moreactive (and tighten) whenexposed to ballistic repetitiveexercise.

In consultation over the yearswith members of basic scienti®cdisciplines, e.g. anatomy andbiomechanics, I have summarizedmy latest thoughts in the bookTherapeutic Exercise for SpinalSegmental Stabilisation in Low BackPain (Richardson et al. 1999).

Group A are `monoarticular'muscles or muscles capable ofcontrolling one joint or one area ofthe spine. These could also bereferred to as `local' muscles. Group

S

B are the `multijoint' muscles thatare capable of moving several jointsat the same time. These muscles arealso phyogenetically the oldest.They could be referred to as `global'muscles. This nomenclatureallows clinical disciplines tocommunicate with other basicscience disciplines to facilitateresearch and learning.

1. It has been suggested thatpostural muscles, whenstressed through overuse tendto shorten, whereas phasicmuscles tend towards disuseand weakness. Expand on whyyou consider this suggestedmodel valid, and if not why not?

I think these are confusing terms.Group B (multi-joint) are thepostural muscles. `Postural' doesdescribe one of the functions of thisgroup as they are the muscles oftenused to e�ciently control theupright posture, e.g. hamstringsrather than gluteals in standingposture. The `phasic' term for groupA is a little more di�cult to explain.In studying lack of use in animalmodels these muscles, motor unitsand muscle ®bres have a tendency tochange from tonic to phasic withdisuse and perhaps with joint injury(Appell 1990).

2. It has been suggested thatdynamic phasic muscles whichtend to weakness contain apredominence of slow twitchType11 ¢bres and that postural

OCTOBER 2000


muscles which tend toshortening contain apredominence of Type1 ¢bres

Not correct. Muscle ®bre types inhumans are di�erent to animal andbird models. Mostly a geneticallydetermined percentage in eachmuscle. There are some exceptionssuch as soleus. It is likely thecontrol, rather than muscle ®bres,which is important (Edstrom 1970,Kuno 1984).

3. The designation of musclesas stabilizers (deep, slowtwitch) with a propensity toweaken and lengthen; andmobilizers (super¢cial, withpropensity to shorten andtighten) is a more recentcharacterization. Furthercatagorizations occur withinthis model including `primary'stabilizers (unable to providesigni¢cant joint movement) and`secondary' stabilizers (able tostabilize and move joints) and`tertiary' stabilizers (which canat times provide defensiverigidity). Expand on why youconsider this suggesed modelvalid, and if not why not?

When teaching joint stabilizationexercises speci®cally, I had taken theclinical nomenclature of MargaretRood of stabilizers and mobilizersas it was in line with my thoughts onmuscles designed for a stability role(Richardson & Bullock 1986). Theseterms are good for teachingphysiotherapists but I found thatthey did not allow communicationwith other disciplines so importantfor research and furthering

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knowledge. In our recent text otherterms are used.

4. For the most part stabilizermuscles are similar to phasicmuscles, while mobilizermuscles are similar to posturalmuscles. However, thequadratus lumborummuscleappears to be the source ofconfusion. How do you classifythis muscle? Similarly, can youcomment on how you classifythe

. multi¢dus,



Quadratus lumborum consists oftwo functionally di�erent parts(Bergmark 1989). (Medial ®bre arelocal spinal segmental stabilizers,and the lateral ®bres global, actingto assist lateral bending). `Themedial portion of the quadratuslumborum may in the future beshown to be functionally separate tothe lateral part of the muscle andcontribute directly to the segmentalsupport of the spine.' (Richardsonet al. 1999).


I do not think the percentage of ®bretype determines categorizations.They will determine how well aperson can optimally perform, i.e.endurance athletes have high slow

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twitch percentage but thispercentage is usually high in all theirskeletal musculature.


For practical clinical value I thinkmonoarticular and multijoint arevaluable terms for the musclescontrolling the perpheral joints. Thespine is more complicated. For themuscles controlling the spine andpelvis, I recommend Bergmark'scategorization into local and globalmuscles based on how well theystabilise the joints or transferexternal load. Local and global canbe used for the peripheral joints aswell.

REFERENCES

Appell HJ 1990 Muscular atrophy following

immobilisation: a review. Sports

Medicine 10: 42±58



Acta Orthopaedica Scandinavica 230

(suppl): 20±24

Edstrom L 1970 Selective atrophy of red

muscles in the quadriceps in long

standing knee joint dysfunction. Journal

of Neurological Sciences 11: 551±558

Kuno M 1984 A hypothesis for neural control

of the speed of muscle contraction in

the mammal. Advances in Biophysics 17:

69±95

Richardson CA, Bullock MI 1986 Changes in

muscle activity during fast alternating

¯exion-extension movements of the knee.

Scandinavian Journal of Rehabilitation

Medicine 18: 51±58

Richardson C, Jull G, Hodges P, Hides J,

1999 Therapeutic exercise for Spinal

Segmental Stabilisation in Low Back

Pain, Churchill Livingstone, Edinburgh

OCTOBER 2000


Response from Pamela W. Tunnell

Position Statement

The questions addressed in thisdiscussion are complex, especiallythose of the correspondence betweenmuscle ®bre type and whole muscledesignations. A good deal ofconfusion arises from the impreciseuse of terms such `tight', `weak',ìnhibited', òveractive', òveruse'and ùnderuse' and this can perhapsmost easily be cleared up. Humanmuscles are built to provide us withconsiderable versatility and foradaptability and thus they are tosome extent structurally variableand individualized. When we docategorize them into two groupsfor ease of discussion andunderstanding of their commonfeatures, we create generalizationsthat are useful but do notadequately explain every muscle.It is essential to bear in mind thatbalanced and appropriateco-activation of both muscle groupsis required for normal posture andmovement, however we choose tocategorize them. Each system ofmuscle classi®cation discussed belowhighlights a highly clinically relevantaspect of the muscular system whichis important to the management ofour patients.

1. It has been suggested thatpostural muscles tend towardsoveruse and eventualshortening, whereas phasicmuscles tend towards disuseand weakness. Expand on whyyou consider this suggestedmodel valid, and if not why not?

This model describes the conditionof muscle imbalance that often

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


PamelaW. Tunnell DC33 Nutmeg Ridge Ridge®eld, CT 06877

203-438-4800, USA

E-mail: ptunnell@ridge®eld-ct.com

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develops within the skeletalmusculature in which one groupof muscles tends to becomeoveractivated and tight while theother tends to become inhibited andweak (Janda 1978; Jull & Janda1987). These classi®cations arosefrom Janda's clinical observationand research (Janda 1978) and arenot readily explainable by theanatomical, histological,biochemical and physiologicalattributes of the muscles (Janda1984). While this condition ofmuscle imbalance may beprecipitated by injury and pain, itneed not be. Aspects of individuallifestyle such as stress, fatigue,emotional state, and inadequatepropriosensory input due to lack ofvariety of movements and sedentarylifestyle are common causes ofmuscle imbalance (Jull & Janda1987). In light of this discussion, it isinteresting to note that in manypublications describing thissituation, Janda refrains from usingthe terms `postural muscles' and`phasic muscles' to describe thesemuscle characteristics and insteaduses the terms `tightness prone' andìnhibition prone' muscles. In thismodel, the `postural' muscles arethose used to maintain the mosttypical functional posture ofhumans, single leg stance. This isconsidered to be the case becausegait is the most typical function ofman and at least 85% of the gaitcycle is spent in single leg stance(Janda 1963).

It is important to understand thatthe terms òveractive' and ìnhibited'refer to altered neurological statesof a muscle. In an òveractive'muscle, the threshold of activation islowered; and the muscle may beactivated earlier and more oftenthan normal and may be included inmovements or functions in which itwould normally be silent. Aninhibited muscle exhibits an elevated

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threshold of activation and is leftout of movements where it wouldnormally be included (Janda 1980).The terms `weak' and `tight', on theother hand, refer to biomechanicalproperties of muscle. Weaknessdenotes a loss of muscle strengthand tightness denotes shortening orloss of muscle extensibility due tostructural changes such as ®brosis orproliferation of the non-contractile(connective tissue) elements of themuscle.

Detailed clinical observation ofpatients including routineassessment of muscle extensibility,coordination, movement patternsand strength, as well as closeobservation of individuals in routinesituations in daily life have shownthat the patterns of muscleimbalance described by Janda arevery frequently found. The degree oftightness or weakness varies fromindividual to individual, but thepattern of tightness and weaknessrarely does. In my clinicalexperience, exceptions to thispattern are infrequent enough thatthis ®nding is a signi®cant one inand of itself and serves as a reminderthat an especially thoroughassessment is in order to shed lighton the factors at work in theindividual's motor system. I ®nd thismodel itself to be highly clinicallyvaluable both in assessing theunderlying imbalance which may setthe stage for an acute or chronicpain episode and for anticipating thetype of imbalance which maydevelop after a trauma and beingable to take steps to normalize itearly on.

2. It has been suggested thatdynamic phasic muscles whichtend to weakness contain apredominence of slow twitchType II ¢bres and that posturalmuscles which tend to

OCTOBER 2000


shortening contain apredominence of Type I ¢bres:Please comment

Here I ®nd it useful to distinguishbetween classi®cation systems usedfor muscle ®bers and those used fordesignating whole muscles.Although as many as eight di�erentmuscle ®bre types have beenidenti®ed (Romanul 1964),discussions of muscle ®bre typeoften focus on two main types calledType I and Type II ®bres. A third,intermediate type is also oftendiscussed in which the Type II ®bresare subdivided into Type IIA andIIB. Type I (tonic/postural) muscle®bres correspond to red muscle.Their metabolic energy is derivedfrom the oxidative metabolism ofglucose, therefore they contain highlevels of myoglobin which bindsoxygen in muscle and low amountsof enzymes used in anaerobicmetabolism. They have a slowtwitch time (100 ms) and are slowfatiguing. These properties makethem capable of prolonged, low-intensity work and they aretherefore considered to be wellsuited for endurance andstabilization. Type I ®bres compriseabout 40% of most human muscles(Garoutte 1996).

Type II (phasic) muscle ®brescorrespond to white muscle andderive their metabolic energy fromthe anaerobic metabolism ofglycogen. They contain low levels ofmyoglobin and high levels ofATPase and myophosphorylase, theenzymes used in this anaerobicprocess. They have a fast twitch time(30 ms), are rapidly acting andincapable of continuous activity.Type IIB ®bres are fast-fatiguingand Type IIA ®bres, an intermediatetype, are more fatigue resistant.Type II ®bres make up about 60%of most human muscles and aredescribed as being rapidly acting®ght-or-¯ight muscles (Garoutte1996). In humans, no skeletal muscle

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consists solely of slow or fast twitch®bres and there are numerousintermediate forms. Each musclecontains variable numbers of slowand fast ®bres depending on thespeci®c functions of the muscle(Ng et al. 1998; Garoutte 1996). Thiscreates considerable versatility andadaptability in functional potential;therefore, in my opinion, attemptsto classify muscles into just twosubgroups may be oversimpli®edand potentially misleading.Proportions of ®bre types within amuscle are believed to be largelygenetically determined but havebeen shown to be readily altered bytraining, immobilization and pain(Jull and Richardson 1994; Garoutte1996; Hides 1994; O'Sullivan 1997).Each motor unit within a musclecontains ®bres of only one type, thatis, each motor neuron activates®bres of only one type and the typeof ®bres in a motor unit has beenshown to change in response toaltering the innervation to themuscle. Evidently it is the frequencyof incoming action potentials thatdetermines the biochemical makeupof the ®bres, as a slow twitch musclestimulated rapidly converts to fasttwitch (Buller 1960). Smaller motorunits, usually made up of Type I®bers, have a lower threshold ofactivation and are thereforerecruited ®rst in a musclecontraction.

The designation of whole musclesas postural or phasic is not clear cutwhen considering the relativepercentage of Type I and Type II®bres alone. Additional aspects ofmuscle architecture are consideredto be important determinants ofthese designations but detaileddiscussion is beyond the scope ofthis paper. Among these are theshape and arrangement of ®bres(fusiform vs penniform), the numberof joints crossed by the muscle,the muscle's function, the depth ofthe muscle and the location andangle of its attachments relative to

238


the joint (Hamill 1995, Norkin1992).

In summary, many factors enterinto the designation of a muscle aspostural or phasic. Chief amongthese seem to be the neural input tothe muscle and how the muscle isused in the body (Buller 1960),which varies from person to personbased on individual motor patternsand habitual activities, among otherthings. In the most clear-cut andsimpli®ed situation, we might like to®nd that postural muscles contain ahigher percentage of slow-twitch,Type I ®bres and that phasic musclescontain a majority of fast-twitch,Type II ®bres. However, ®bre typedoes not seem to to be the only norperhaps the most important factorinvolved. In general, as it is acomplex subject, I think we have yetto fully appreciate the signi®cance ofindividual motor variations, whichamount to di�erences in neuralregulation and may have animportant in¯uence in determiningmuscle structure.

3. The designation of musclesas stabilizers (deep, slowtwitch) with a propensity toweaken and lengthen; andmobilizers (super¢cial, withpropensity to shorten andtighten) is a more recentcharacterization. Furthercategorizations occur withinthis model including `primary'stabilizers (unable to providesigni¢cant joint movement) and`secondary' stabilizers (able tostabilize and move joints) and`tertiary' stabilizers (which canat times provide defensiverigidity). Expand on why youconsider this suggested modelvalid, and if not why not?

This model seeks to describe thefunctions served by various skeletalmuscles and to categorize themaccording to the predominant

OCTOBER 2000


roles they play in the motor system.Because stability and mobility arekey functions of muscle, becausemuscles can and do adapt theirfunction to the demands placedupon them, and because stabilityrequirements are not the same for alljoints, I ®nd that functionalclassi®cation of muscles is clearestand most meaningful when the jointand function in question are clearlyspeci®ed. Any muscle of the body iscapable of providing stability duringsome function (Jull and Richardson1994; Richardson et al. 1999) and inmy mind it would be anoversimpli®cation, no matter howattractive, to imply that any musclehas only one function.

The problem of spinalstabilization is unique. The term`axial organ' has been coined to referto the spine and highlights the factthat the spine, while composed ofmany segments, has a uniquefunction as a distinct and uni®edorgan within the motor system. Itfunctions as the structural axis orcore of the motor system aroundwhich the peripheral trunk andextremities are organized(Richardson et al. 1999). However,the spine can only functione�ectively in this capacity withadequate neuromuscular activityand coordination (Gardner-Morseet al. 1995). This requiresperception/proprioception,planning, timing, coordination,speed, endurance and strength.Thus, anticipatory organization ofthe axial organ is requisite toposturing or movement of the acral/peripheral elements of the body.Research has demonstrated the feed-forward spinal stabilizationresponse that occurs beforeintentional movement begins(Cresswell 1994). The CNS mustchoose a postural set for eachactivity, whether static or dynamic.Thus, e�ective stabilization of thespine consists ®rstly of stabilizationof the individual spinal segments

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into a spinal posture which isboth safe for the spine andbiomechanically consistent with thetask at hand, and secondly ofactivity of the more peripheral trunkmuscles which transfer loads fromthe trunk to the pelvis andminimizes the loads experienced bythe spinal segments (Bergmark1989).

Stabilization of peripheraljoints, while as important, does notinvolve this same problem. I ®ndthis functional model ofclassi®cation valid and useful but Iam inclined to use somewhatdi�erent terminology, especiallywhen discussing spinal stability(see Question 6).

4. For the most part stabilizermuscles are similar to phasicwhile mobilizer muscles aresimilar to postural. However, thequadratus lumborummuscleappears to be the source ofconfusion. How do you classifythis muscle? Similarly, can youcomment on how you classifythe

. multi¢dus,



Based on the factors discussed inQuestion 2, I disagree thatstabilizers are mostly similar tophasic muscles and mobilizersto postural. As de®ned by Norris,stabilizers are similar to postural insome important features, includingtheir slow-twitch nature and beingwell suited for endurance activities(Norris 1999). Based upon clinicalexperience and current research(McGill 1996), I consider thequadratus lumborum (QL) toexhibit characteristics of bothcategories and to possibly havefunctionally distinct parts within themuscle. I view it as both a peripheralspinal stabilizer which tends to

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overactivity and tightness and, in itsmedial ®bres, a segmental stabilizerof the spine. The QL can reactvariously, for example, in cases ofcoronal plane dysfunction orasymmetry such as scoliosis, pelvicobliquity or poor lateralstabilization of the pelvis duringgait. In these situations the QL maybecome overactive and tight on oneside and inhibited and weak on theother. This example accents thereality that in the end a muscle'sfunction depends on the forces it isresponding to and the task it istrying to accomplish for the body.While there are many principles offunction that help us clinically, ourgoal should be to assess andunderstand each patient as they arerather than making them ®t into thecategories we have previouslydescribed.

I consider the multi®dus andtransverse abdominis to be intrinsicspinal stabilizers, both of which tendtowards inhibition and weakness indysfunction (Cresswell 1993;Richardson et al. 1999; Hodges1999; Cholewicki et al. 1997).Finally, I view the rectus abdoministo be a secondary spinal stabilizer(contributing to sagittal planestabilization of the spine as whenpushed unexpectedly from behind)which also tends toward inhibitionand weakness. Research has shownthat the rectus abdominis is oftenoveractivated in an uncoordinatedfashion when the deeper abdominalmuscles do not function well, that itsfunction is not properly dissociatedfrom that of the deeper abdominals(Richardson et al. 1999) and myclinical experience bears this out. Atthe same time I ®nd that the rectusabdominis itself is often poorlytoned, elongated and weak orinhibited and I do not ®ndcontradiction in these descriptions.The rectus abdominis is, in my view,simply the muscle within the overallpoorly functioning abdominal wallwhich activates in attempting to

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substitute for the poorly functioningdeeper muscles.


The characterizations made aboveare based primarily on acombination of clinical experienceand understanding of motor systemfunction with a secondarycontribution from available researchon muscle ®bre types. Althoughclearly the distribution of ®bre typesmust be consistent with thefunctions of the various muscles,neither our understanding of thecomplexities of motor function northe research on ®bre types issu�cient enough to allow us toclearly explain the relationships atpresent. Since many intermediateforms of ®bre types have beenidenti®ed, it makes sense thatclassi®cation of muscles into twogroupings, while helpful in theirsimplicity, are bound not to be ableto accurately describe all situations.

It may be that one conclusion tobe drawn is that of humanadaptability and versatility. Manymuscles play a role both inmovement and in stabilization; theypossess the ®bre distributions andneural capability to activate eitherfunction as needed. Patterns ofmotor activity are highlyindividualized. For example, gait isone of the most basic humanmovements and yet it is soindividualized that we are often ableto recognize an individual at adistance by the distinctive featuresof their carriage and movement longbefore we can visually discern theirfeatures. If muscle ®bre type isdetermined in part by how weactivate our muscles this would helpto explain the wide variations in®bre types and the lack of clear

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preponderance of one ®bre type overanother in many muscles. Factors ofindividual variability in motorregulation are rarely taken intoaccount in research trials and indeedwould be very di�cult to take intoaccount in study design.Additionally, when considering howthe muscles respond in pain anddysfunction, I believe there arereactions which occur fairlyuniversally (Richardson et al, 1999)as well as those which areindividualized. This wouldcontribute another source ofvariation in attempting to correlatemuscle ®bre types with musclefunction.

6. Do you have a di¡erent wayof designating, characterizing,muscles which is of practicalclinical value to you?

When assessing overall muscleimbalance I use Janda's designationsof muscles prone to overactivity/tightness and those prone toinhibition/weakness, bearing inmind the factors of individualvariability discussed previously aswell as the fact that some of thedesignations are unclear orunknown at present. I ®nd theseterms somewhat lengthy and it isunderstandable that they becomeshortened into more convenientones. At the same time, the presentconfusion demonstrates to me that itis worth using a few extra, moreexplicit words for the sake of clarityin communication since it is unlikelythat in any audience all listeners/readers will have enough familiaritywith the complexities of the subjectto not become confused by the moreabbreviated terms.

When discussing spinalstabilization, I prefer to use the term`intrinsic spinal stabilizers' to referto the short, intrinsic muscle of thespine proper and to muscles withsegmental spinal attachments whichare well positioned for segmental

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spinal control. This includes theintertransversarii, interspinales androtatores, which may functionchie¯y in the proprioceptive aspectof segmental stabilization (Bogduk1991), the multi®dus and transverseabdominis (Hodges 1999). I use theterm `secondary spinal stabilizer' torefer to the more peripheral trunkmuscles like the erector spinae,rectus abdominis, external obliqueand quadratus lumborum whichplay a crucial role in spinalstabilization not at the segmentallevel but rather by controlling andtransferring loads from the trunk tothe pelvis; these muscles are alsocapable of producing movement andtorque.

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