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Peter OUSullivanlance Twomey

o RI G IN A L ARTie LE

It rnb min I u I

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This study investigated patterns of abdominalmuscle recruitment during the abdominaldrawing in manoeuvre in subjects with chroniclow back pain (CLBP) and radiological diagnosisofspondylolysis orspondylolisthesis. Data werecollected using surface electromyography from12 physicallyactiv8 subjects with CLBP and 10controls. Thecontrol subjects displayedan abi lityto preferentially activate internal oblique withminimal activation of upper rectus abdominisduring the action of drawing in the abdominalwall. The group with CLBPwere unable toachieve this. This finding may reflect thepresence of neuromuscular dysfunction in thisgroup. Further study is required to investigate ifthese findings are linked to theabil ityofpatientswith GLBP to provide dynamic stability of theirlumbar spine.[O'SullivanPB, Twomey L,Allison GT, Sinclair J,Miller K and Knox J: Altered patterns ofabdominal muscle activation in patients withchronic low back pain. Australian Journal ofPhysiotherapy 43: 91-98]

Key words: Backache;Electromyography; Exercise;Muscles

PB O'Sullivan DipPhty,GradDipManipPhty isaPhD student at Curtin University of Technology,Perth, and part time private practitioner.LTwomey BApPSc,·BSc(Hons), PhD.is Professorand Vice Chancellor of Curtin Universtity ofTechnology, Perth.GT Allison BAppSc(Hons},MEd, BEd(Honsl, PhDis a lecturer in the School of Physiotherapy,Curtin Universtity of Technology, Perth.

he ligamentous spine is known tobe biomechanically unstable atloads far less than that of

bodyweight (Nachemson 1966).Because of this the neuromuscularsystem must fulfil the supplementaryand adaptive roles of maintainingpostural stability whilst controlling andinitiating movement (Crisco andPanjabi 1991). It has been suggestedthat when the segmental stability of theanatomical restraints is compromised,such as in the case of symptomaticspondylolysis or spondylolisthesis, theneuromuscular system may be capableof compensating to provide dynamiccontrol to the lumbar spine duringfunctional tasks (Panjabi 1992).Iti light of this potentially important

role of the neuromuscular system,recent studies have focused on thefunction of different muscles of thetrunk in order to determine theirability to provide dynamic support tothe lumbar spine (Cresswell etal 1994,Cresswell and Thorstensson 1994,Crisco and Panjabi 1991). Internal

J Sinclair BAppSc, GradDipManipPhty is amanipulative physiotherapist in New Norcia.WA.Kim Miller BAppSc, GradDipManipPhtyischargephysiotherapist in the Outpatients Departmentof Royal Hobart Hospital.Jacqui Knox BAppSc, GradDipManipPhty is aprivate practitioner in the UK.

oblique (10) and in particulartransversus abdominis (TA) aremuscles known to· provide rotationaland lateral control to the spine, whilehelping maintain levels of intra­abdominal pressure and impartingtension to the thoracolumbar fascia(Cresswell et a11992, Cresswell et·al1994, .Cresswell.and Thorstensson1994:, Teshet aI1987). It is consideredthat the co-activation of the deepabdominal muscles with lumbarmultifidus increases the lumbar spinestiffness, thereby enhancing itsdynamic stability (Aspden 1992).

Exercise programs designed toimprove the general function of theabdominal muscles have been widelyadvocated by physiotherapists for thetreatment of low back pain for manyyears (Kendall et al 1971, Kennedy1980). Until recently, the justificationfor carrying out these exerciseprograms has been based largely onclinical knowledge and empiricalassumptions, without definitive

Correspondence: Peter BO'Sullivan, School ofPhysiotherapy, Curtin UniverstityofTechnology,Selby Street, Shenton Park, Western Australia6008.

From Page 91evidence of muscle dysfunction orregard for different diagnostic clinicalgroups.

Research investigating differentabdominal exercises has confirmed thatsome exercises·are more appropriatefor specifically activating the deepabdominals (Tullet a11995, Strohl et al1981). The abdominal drawing inexercise is known to activate the deepabdominal muscles with littlecontribution by the rectus abdominis(RA) (JulIet al1995, Strohl et aI1981).For this reason, it has beenhypothesised that this manoeuvreresults in an ideal pattern of muscleactivation for facilitating the dynamicstabilising role of the deep abdominalmuscles (Richardson and Jull 1995).

There is growing evidence in theliterature to suggest that the presenceof CLBP is associated with dysfunctionin the deep abdominal muscles(Hodges and Richardson 1996, Hodgeset al 1996). There is also evidence toindicate that when a muscle or a groupofmuscles is weakened, there isatendency for subtle shifts in the patternof motor activity to occur, enabling theother synergistic muscles to generatethe necessary force required forfunctional tasks (Edgerton et al 1996)..This is lmownasmuscle substitutionand is often difficult to observe byunskilled gross muscle testing but canbe detected using EMG (Basmajianand Deluca 1985). Experiencedclinicians have reported the presenceof these subtle changes or shifts inpatterns of muscle activation withinthe abdominal muscles in subjects withCLBP. These patterns have beendescribed asa substitution or over­riding activity by the RA muscle(predominantly upper RA), and theexternal oblique muscle duringattempted activation of the deepabdominal muscles aull et a11991,Richardson and]u111995, Robison1992).The aim of this study was to

investigate whether or not. differencesin patterns of abdominal activationoccur between synergists in a definedCLBP population during theabdominal drawing in manoeuvre. The

-0 RI Gt N A1 A RTtC l E

population. investigated consisted ofphysically active persons withCLBPconsidered to be attributable to theradiological diagnosis of spondylolysisor spondylolisthesis. This conditionwas chosen as it is considered to be themost obvious manifestation of osseo­ligamentous lumbar instability (Pope etal 1992). Thus it could be argued thatthe·correct functioning of thesemuscles would be critical in thesesubjects to ensure the maintenance ofoptimal spinal stability of the affectedregion. Only physically active personswith this condition were permitted toenter the study and were comparedwith similarly active pain free controls.This selection criteria ensured that anydifferences in the levels of generalactivity between the groups would notbias the findings. Furthermore, anyfindings in the CLBP group could notbe attributed simply to disusesecondary to low activity levels in thegroup.

MethodsSubjects were classified into a pain freecontrol group and CLBPgroup.Twelve subjects with CLBP wereselected from a larger study groupparticipating in a clinical trial, on thebasis that they were physically activeand carried out a minimum of three30-minute aerobic activity sessions perweek. Inclusion criteria were restrictedto subjects of either gender whosesymptoms ofCLBPwere recurrentand had persisted longer than threemonths with no sign ofabating. Thesubjects entered the study only if theirsymptoms and clinical presentation wasconsidered to be attributable to theradiological diagnosis of spondylolysisor spondylolisthesis by their medicalspecialist (Nazarian 1992). Subjectswere excluded if they had: a clinicalpresentation that·was consideredunrelated to the presence of thespondylolysis or spondylolisthesis bythe treating medicalspecialist(Nazarian 1992); a diagnosedpsychological illness; undergone spinalsurgery; a diagnosed inflammatoryjoint disease; or displayed overtneurological signs (sensoryparaesthesia or motor paresis). Subjects

AUSTRAliAN PHYSIOTHERAPY

were recruited from physiotherapypractices, general and specialistmedical practices and painmanagement clinics in the Perthmetropolitan area.

The control group consisted of 10subjects of similar age to the subjectswithCLBP. Entry to the trial was onthe basis that they participated inregular weekly aerobic activity(minimum of three 30 minute sessionsper week). Control subjects wereexcluded if they had experienced anyepisodes of back pain in the precedingsix months. Subjects were recruitedfrom the local community. Ethicalapproval for the study was granted bythe Human Ethics Review Committeeof CurtinUniversity of Teclmology,Western Australia.

A between subject control design wasemployed. Both the subject andtherapist instructing the exercise wereblind to the surface .eleetromyography(SEMG) data during the testingperiod.

After signing a consent form, thesubject's height, weight and selfreported average weekly activity levelswere noted. Unpaired statisticalanalysis revealed no significantdifferencehetween the groups on the'basis of these measures. Subjectcharacteristics for both groups areoutlined in Table 1. None of thesubjects with CLBPwere seekingcompensation at the time of testing,nor were they unable to work due totheir condition.

Activity of the 10 and upper RAmuscles was measured unilaterallyusing SEMG. The EMGequipmentused consisted of a Medelec PA63preamplifier (Medelec MS6) which wasconnected to an AAG Mk IIIamplifier/filter (Medelec).Thegainsetting was50mv/div and the bandwidth filtering wasS-800 Hz. Theoutput from the amplifiers weresampled at 1600Hz via MacAdios andrecorded onto a Macintosh IIcomputer.

Analysis of the SEMG data·wascarried out during the abdominaldrawing in manoeuvre as described byRichardson et al (1992). This waschosen as the drawing in manoeuvre

AUSTRAliAN PHYSIOTHERAPY oRIG IN A l ARTICLE

the navel up towards their head and intowards their spine, so as to hollow theabdomen. The head and upper trunkwere to remain stable and subjectswere not permitted to flex forward,push through their feet or tilt theirpelvis (as noted by the pressurebiofeedback monitor 'under thesubject's feet) (Richardson etaI1992).The exercise was repeated until thesubject understood the procedure andwas able to carry it out whilstbreathing. Once this wasdemonstrated, the subject carried outthe same procedure, gently flatteningthe hack to gain a steady rise oflOmmHg on the pressure gauge. lftheinstructor noted that the procedurewas being performed incorrecdy, thesubject was instructed how to correctit.

The electrode sites were thenprepared as described by Gilmore andMeyers (1983). Two electrodes wereplaced Zcm apart, over the right upperRA muscle (Scm inferior to the xiphoidprocess and 3cmlaterallyfrom the midline) and over the right 10 (3cmcephalad and medial to the anterior

has been shown in the normalpopulation to preferentially activatethe deep abdominals with minimalactivation ofRA(Jull et a11995,Strohlet al 1982). This testing protocol hasbeen validated in the normalpopulation (Hall et a11995) and shownto be repeatable between trials(Richardson et al 1992). In recenttimes, this protocol has been widelyadopted by physiotherapists working inclinical practice as an appropriatemanner of evaluating and training thefunction ofthe deep abdominalmuscles. It is during this form oftesting that the clinical observations ofmuscle substitution have been reportedto occur in theCLBP population Gullet al 1991, Richardson and Jull 1995,Robison 1992).

Each subject was positioned in supinewith hips flexed to 45 degree (crooklying) and a pressure biofeedbackmonitort was placed under the lumbarlordosis .between Sl and Ll,withanother beneath the subject's feet. Thepressure was set to 40mmHg. Eachsubject was instructed to contract theirdeep abdominal muscles by drawing

)1111>;! i!i'fit!i[i:~\1:r:i:;!<!>::

li"i~~Ptoms:;;i!jiiJ:! ;:·:rs:evelof defectIi i!:t)1!:i:11:tlI"~deof slip

111!'I~ualanaloguescale -i;II~~tlk~g~sP= :~:Tsity over(i~~;~icllr()nic low back pain

CLBP*n= 12

23 (16- 28)5,Female7 Male74(62- 97)173 (151 - 190)30 (3-72)

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superior iliac spine) (Goldishet al1994, Pope etaI1986).An earthelectrode was placed over theacromium process.

Contractions were performed foreach muscle to ensure the correctplacement of the electrodes and thatcross talk between the recording siteswas negligible (Richardson et aI1992).For the upper RA, the subject wasasked to flex the head and upper trunk,and for the TO the subject wasinstructed to. gendy draw in the lowerabdominal wall muscles (Strohl et al1981).

Testing protocolAmplitude normalisationofSEMGdata: Each subject initially performed adouble leg raise. The instruction wasto raise both feet lcmoff the plinthand hold for SSe VVllen the subjecthadgained.a steady isometric contraction,the SEMG ofthe abdominal muscleactivity was recorded for 3s. Tworecordings were made. This sub­maximal.isometric contraction wasused to normalise the SEMG data.This decision was made on theknowledge that maximal contractionsfor muscles of the trunk are reportedto be unreliable in both normal(McGill 1991) and LBP populations(Beimborn and Morrissey 1988).Submaximal contractions, on the otherhand, have been shown to be morereliable than maximal contractions(Allisonet al1993), and areable to beperformed by subjects with back pain.The double leg raise was thesubmaximal contraction selected as it isknown to activate all the abdominalmusculature to stabilise the pelvisduring.the manoeuvre (Basmajian andDeluca 1985). It isa simple,symmetrical motor strategy whichapproximates the muscle length andtension of the. skill task beingexamined. Pilot investigations hadshown this movement pattern to resultin high levels of activation of bothmuscles relative to background noise.Statistical analysis of this data revealedthat the double leg raise resulted inactivation of both muscles to similarlevels of electrical output,and wasrepeatable within and between testing.,.

ORIGJNAl ARTICLE AUSTRAlIAN PHYSIOTHERAPY

0.1140.2350.035*

p ..valuefordiff~rellcebetweengroup~

pV~l1efor

dUferen.cebetwee1l1llllscles

CLBPgroupn=12

0.342 (0.28)0.629 (0.49)2.41 (1.70)

In.ternaloblique

The results indicate .that significantdifferences exist between the CLBPand control groups on the basis ofwhich abdominal activation strategywas utilised to .achieve and sustain alOmmHg rise on the pressurebiofeedback monitor during theabdominal drawing in manoeuvre4 The

RA(Z(1,21) =-1.58,p= 0.114) and 10(2(121)= 1.18, P= 0.235 (Table 3).However, when .the ratio of activation.(IO/RA) was calculated, a significantdifference between groups wasdetected(2(121)= -2.11, p= 0.035) (Table 3 andFigUre 2).

D<iscussion

Controlgroupn==lO

0.188 (0.14)0.837 (0.44)8.74 (9.05)

Rectus abdoIIlinisInternalobliqueRatios TO/RA

* indicatesstatistical significance

CLEP n=12

OutcomemeasuresMean (SD)

GroupMeatl(SD)

Table 3.Means and standard deviations (SO}ofthe.abdominalratios.(internaloblique/rectus abdominis) (lO/RA) for the<control andchronic IOlN back ·.pa.in (CLBP)groups (root mean squared .. normalisedsurf8ce electromyography).

* indicates statistical significahce

lable2.. ...•.• •...• ....<... . < .. .. . .. .. . >:.:M~~Il~Md~a.ndarddeviation$ (SDl of reelusaIJ.w....inisandi~rllal.obliquefort~ .•e•.•..coll.tr~ •.I· ..a·nd·•.c.hron..ic....I.o""..•.bCl.c.k ...pain:.. (·CLB.P)... grOIJPs::.(·ro.ot ..mean...squared....normalisedsurfaceelectromyog~aphy). .

The control group showed asignificantly greater level of activationin the 10 compared with upper RAduring the abdominal drawing inill.·. anoeuvre (~9)=-248,P= 0.005)(Table 2 and fi-igure 1). The CLBPgroup on the other hand showed aslight difference in means but nostatistically significant difference(2(1.\1) = -1.8, p= 0.071) between theleve s of activation of10 and the RAduring the contraction (Table 2 andFigure 1).

There were no statistically significantdifferences between the groups whencomparing the level of activity of the

Results

From Page 93sessions (ICC - 0.85-0.90). It isrecognised by the authors that as thenormalisation contraction is sub­maximal, the SEMG findings can beinterpreted only with regard to relativelevels of muscle activation and not asapercentage of maximum voluntarycontraction. Indeed, this is thelimitation of performing SEMG signalamplitude analysis of muscles of thetrunk and in pain populations. Thetotal ofthe root mean square data wasused to normalise the SEMGdata forthe abdominal drawing in exercise.

Abdominal drawing in exercise: Eachsubject performed three trials. Foreach trial, they were required to gain apressure rise of 10mmHg on thepressure biofeedback monitor andmaintain this level for lOs. The last Jsof each trial was recorded to disk.

The electrocardiographic activity wasselectively removed from the rawsignal by visual inspection to avoidcontamination of the results. The totalroot mean square of the SEMGactivity of the upper RA and 10 wasthen calculated. The data were thenamplitude normalised using the doubleleg raise data for these muscles. Fromthis the ratio of activation of the 10relative toRA was calculated (IOfRA).

Non-parametric .statistical analysiswas performed on the data due to thesmall sample groupsize.WilkoxonSigned Rank Test for pairedcomparisions were performed on thedata to assess for differences hetweenthe level of activation of RA whencompared with the 10 for both groupsduring the abdominal drawing inmanoeuvre. Man....'Whitney U Tests forunpaired comparisions were performedon the data to assess for:i) differences between the groups

based on the relative level ofactivation of RA and the 10muscles; and

ii) differences between the groupsbased on the calculation of theratio ofactivation between the 10relative taRA.

The level for statistical·significancewas set at the 95 per cent confidencelimit.

AUSTRAliAN PHYSIOTHERAPY

35 0

30

2520

(j 15

~ 10

5

0Control CLBPCLBPCLBP

o

Control

o

Control

~f"

~.g:~~•• 0.4:~ ,

~ 0.2o

figure 1.Normalised surface electromyography (SEMS) of the rectusabdominis(RA) and internal oblique (U)) for the control andchronic low back pain (ClBP) groups (Box plots show median,inter-quartile range and 90th and 10th percentiles).

Figure 2.Normalised surface electromyography (SEMG)- ratios ofactivation (internal obiique/rectusabdominis) for the control andchronic low back pain (ClBP) groups (Box plots show median,inter"'quartilerange and 90th and 10th percentiles).

results indicate that the controlsubjects had the ability topreferentially activate 10 withoutsignificant activation of the upper RAduring the manoeuvre, whereas theCLBP group was unable to isolate thispattern to the_same degree. Thesefindings provide support to the claimmade by clinicians that the presence ofCLBP is often associated with a changein the pattern of abdominal activationsuch·that RA tends to substitute duringattempts to preferentially activate thedeep abdominal muscles (RichardsonandJull1995b). Furthermore, thesefindings may represent the presence ofa neuromuscular dysfunction of theabdominal musculature in this specificCLBP population. The differencesbetween the groups indicate an alteredpattern ofabdominal activation orrecruitment in the CLBP group whensustaining the abdominal drawing inmanoeuvre at a high level ofcontraction. This difference cannot besimply explained by a generaldeconditioning in the CLBP group, asboth groups reported similar physicalactivity levels. The groups differedonly on the basis of the presence orabsence of a CLBP condition.

The presence of four reasonablydistinct large muscle groups withdifferent fibre orientations suggeststhat the functional capacity of the

abdominal musculature is varied andcomplex (Strohl et aI1981). Althoughfunctional differences within theabdominal musculature have beenwidely reported (Cresswell et al 1992,Cresswell et al1994,CresswellandThorstensson 1994, Strohlet aI1981),the muscleswithln the abdominalcomplex function in patterns ofsynergy and do not work incompleteisolation from each other (Basmajianand Deluca 1985). Altered patterns ofsynergy or substitution ina musclecomplex such as theabdominals maynot always be detected by simplycomparing the level of activation ofone muscle in a pathological groupwith that of the same muscle in acontrol group. Consequently,calculating ratios between synergistsappears to be an appropriate way ofhighlighting altered patterns of muscleactivation between different groups ofsubjects. In this study, calculatingratios proved a more sensitive means ofhighlighting differences in patterns ofabdominal activation between theCLBP and control group than simplycomparing the activation levels of theindividual muscles. Other researchershave also employed this method toassess differences in synergisticfunction of the quadriceps muscle,comparing the relative contributions ofvastus medialis and vastus lateralis to

knee joint extension betweenpathological and control groups(Boucher et al 1992, Souza and Gross1991).

Edgerton and co-workers (1996)recently reported a large studyundertaken involving subjects with andwithout spinal pain. Their findingsrevealed that the presence of alteredpatterns ofmuscular activationbetween trunk muscle synergists (inthe form of ratios) were able to predictwith 88 per cent accuracy subjects withpain from controls. They suggest thatthe presence of pain, leading to theinhibition of a specific muscle or agroup of muscles, produces alterationsin the neural strategies of recruitment.This results in the compensatoryrecruitment of other motor units fromsynergists, when performingprescribed motor tasks. Furthermore,they suggest that muscles which arerecruited to compensate for theresulting functional deficits coulddisplay increased force generation andhyperactive EMG patterns. Theauthors indicate that thesecompensations can be detected bychanges in <EMG ratios·within musclesynergies. They conclude byhighlighting the potential of suchfindings for the development ofrehabilitative strategies to up or down-

From Page 95train abnormal reflex responses and re­educate the neural feedback loop.In contrast with the findings of this

study,]ull et al (1995) reported thatthere was no statistically significantdifference in the levels ofactivation ofthe IO,.EO and.RAmuscles.insubjects with LBP compared with~ontrols during the abdominal drawingIn manoeuvre (apart from an increasein the lower RA in the group withLBP). However, they reported aninability ofthe group with LBP toperform the drawing in manoeuvre.Their study differed methodologicallyfr?m this study in a number of ways.FIrst, the present study investigatedabdominal recruitment patterns in adefinitiveCLBP populationrepresenting an impaired passive sub­system (spondylolysis andspondylolisthesis), whereas the lull etal (1995) study investigated anundefined CLBP population.Secondly, they investigated thedrawing in manoeuvre in the·pronelying position, whereas the currentstudy utilised supine crook lying. Itmaybe that subjects have greaterdifficulty in substituting for theactivation of the deep abdominalmuscles in the prone position andtherefore were not able to achieve thesame change in pressure as the controlgroup. Finally, the present studymeasured the SEMG muscle activityonly when the subjects had achievedand sustained for 1Os a rise of10mmHg on the pressure biofeedbackmonitor. In this way both groups werestandardised to achieve a set motortask. In contrastJnIl et al {I995)investigated the level to which theabdominal drawing in could be carriedout. In the light of these differences itwas observed that, in the present study,the control group had minimaldifficulty carrying out the hollowingtask and achieving a steady rise of10mmHg on the pressure biofeedbackmonitor. However,theCLBP grouphad great difficulty achieving the samepressure, and did so only withconsid~rabledifficulty in co-ordinatingbreathing and maintaining the correctpatterns of activation. It appears that in

ORI GINA 1 ART I C l E

order to achieve a rise of 10mmHg, theCLBPgroup had to substitute for theac~on .of the deep abdominalsbyactivating. other synergists (ie upperRA). It should be noted that none ofthe subjects experienced pain duringthe testing, so that pain onset was notable to influencethe.pattern ofactivation.

Altered patterns ofabdominalrecruitment have also been reported ina group of normal subjects at differentlevels of activation when drawing inthe abdominal wall (Hall etaI1995).They reported that a rise of 5 and10mmHg on the pressure biofeedbackmonitor was associated with anincrease in the activity of the antero­lateral abdominals and little change in.the level of activity of upper RA.However, ata level of 15mmHg rise,they demonstrated a trend for an~nc~ease inRA activation. Their studyIndicates that under higher levels of~xertion during the abdominal drawingIn m~noeuvre, normal subjectssubstituted for the action of theantero-Iateral abdominals by increasingthe activation of the RA muscle. Itappears that a similar pattern alsooccurred in the CLBP group of thecurrent study, but ata lower level ofcontraction (10mmHg). It could behypothesised that the findings of thecurrent study either represent thepresence of deep abdominal musclewe~kness in theCLBP group such thatsubjects had to recruit upper RA toachieve the required pressure rise, orthese subjects exhibit an altered patternof neu~omusct.Ilar.recruitment duringabdOmInal activation. To clarify this,further research will need to beconducted to investigate the patternsof muscular activation in theCLBPgroup at differing levels of exertion ina similar manner to that of Hall andco-workers (1995).

The surface electrode site used in thisstudy to measure activity from thedeep abdominal muscles has beenreported to record muscle activitypredominantly from the 10 musclewith a possible contribution from theunderlying TAmuscle (Goldish et al1994, Pope et aI1986), although it ispossible that some cross talk from

AUSTRAliAN PHYSIOTHERAPY

external oblique may have occurred. Itis these deep abdominal muscles thatare considered to be central inproviding dynamic stability to thelumbar spine, yet it appears that thissmall but specific group of subjectswith CLBP were unable topreferentially activate these muscles tothe same degree as the controlsubjects. This supports the findings ofother researchers who have reportedthe presence of deep abdominaldysfunction in subjects with CLBP(Hodges and Richardson 1996, Hodgesetal 1996). Recently, Hodges and co­workers (1996) reported that, insubjects with CLBP, the inability todraw in the abdominal wall correlatedwith a delay inactivation of thetransversus abdominis muscle detected~singneedle EMG during rapid armhft. It would appear likely that in thepresence of deep abdominal muscledysfunction, additional motor unitswill be recruited by synergists (such asRA) in order to perform motor tasks. Achallenge for further research will beto investigate whether these alteredpatterns ofrecruitment of theabdominal muscles can in fact bedetected during the performance <offunctional tasks, in a similar manner tothat carried out by Edgerton and co­workers (1996).

In the normal population,functionaldifferences have been detectedbetween the deep abdominal musclesand RA (Cresswell et a11992,Cresswell and Thorstensson 1994).During trunk loading, the activation ofT A and, toa lesser degree, TO isdirectly associated with increases inintra-abdominal pressure, with littleassociation for the activity ofEO orRA (Cresswell·and Thorstensson1994). It has been suggested that theimportance of the action ofTA inparticular lies in its ability to increaseintra-abdominal pressure and·thusprovide dynamic stability to the lumbarspine without applying an anteriorcompressive or flexion penalty(Cresswell and Thorstensson 1994).Furthermore, the tonic activation oftheTA and 10 muscles duringmovement allows the provision ofdynamic stabilisation to the lumbar

AUSTRAliAN PHYSIOTHERAPY

spine without restricting mobility ofthe ribcage or respiration (Strohl etal1981). On the other hand, high levelsof RA co-activation, may represent afaulty pattern of dynamic stabilisationrestricting freedom of ribcagemovement and therefore respiration,resulting in increased ventralcompressive and flexion forces beingexerted to the lumbar spine.

It should·be noted that the findings ofthis study relate to a small but veryspecific group ofsubjectswithCLBPand therefore cannot be considered asrepresentative of the wholeCLBPpopulation. The authors alsoacknowledge that, due to the smallnumber of subjects involved in thisstudy, the chance ofa Type II error isincreased. Clearly more research needsto be carried out to further validateand determine the clinical significanceandgeneralisability of these findings.

The CLBP subjects gained entry tothis study only if they were physicallyactive and their clinical presentationwas considered to be attributable totheir radiological diagnosis ofspondylolysis or spondylolisthesis, acondition known to compromise theanatomical stability of the lumbar spine(Popeet al 1992). It is our hypothesisthat the findings of the present studymay reflect an inability of theneuromuscular system to provide idealdynamic support to adequatelycompensate for the compromisedanatomical stability ofthe lumbar spinein these·subjects.Certainly there isevidence to support this hypothesis,given that in preliminary reports, there,...education of this motor pattern, andthe specific training ofdeep abdominalmuscle co-activation with thesegmental extensors incorporated intofunctional tasks, resulted in a sustainedreduction in symptoms within thisgroup ofsubjects (O'Sullivan et al1995). Further research is presentlyunder way to determine whether suchfindings are consistent with otherspecific diagnostic groups withCLBP,and what the relationship is betweenother synergists to these patterns ofactivation.

It is the view ofthe authors that the

oRIGI NA l ART I C l E

findings of this study also raise animportant point for clinicians whosetreatment aim is to specifically trainthe deep abdominal muscles. Thepresence ofsubtle changes in patternsof muscle substitution which this studydemonstrates reinforces the need forclose attention ·to·specificity whenprescribing exercise programs. If not,the therapist may risk reinforcingaltered patterns ofsynergistic musclebehaviour which are already present.For example, when training thespecific activation of the deepabdominal muscles in conjunction withthe pressure biofeedback monitor,instructing the patient to achieve aparticular pressure rise on the monitorwithout regard for the quality of themuscle contraction may simplyreinforce the activation of unwantedsynergistic muscle activity frommuscles such asRA during thecontraction. In the early stages ofrehabilitation it maybe moreimportant for the practitioner to focuson the quality of the pattern ofabdominal contraction rather than onthe pressure level achieved on thepressure biofeedback monitor. If thepatient has great difficulty in isolatingthe contraction of the deep abdominalsin supine crook lying, then otherpositions such as four point kneelingand prone, as described by Richardsonand co-workers (1995), may be moreappropriate. Furthermore, whenspecifically training the deepabdominals, the early introduction ofloaded exercise training or generalexercise regimes directed at thesemuscles, prior to the patient learninghow to isolate an appropriate patternof deep abdominal contraction, maysimply reinforce faulty patterns ofmuscle recruitment already present.This concept oEtraining is furthersupported by the knowledge that allthe subjects with CLBP in this studywere exercising at a high level, many ofthem having carried out high intensityabdominal exercise training. Indeed, allof the subjects reported not benefitingfrom such treatment regimens prior toentering the study. In such situations,prescribingfurther high intensityexercise for the treatment of their

condition would appear inappropriate.This view is supported by the assertionof Basmajian (1977) that motorlearning is not simply a process ofstrength training, but also depends onthe patterning and inhibition of motorneurons, with the acquisition of skillsoccurring through the selectiveinhibition of unnecessary muscularactivity in some muscles as well as theactivation of additional motor units'inothers. It is our view that in theclinical setting, inhibiting unwantedsynergistic muscle action whenattempting to facilitate another musclewithin a synergy requires a high levelof skill and specificity with a need forpatience and perseverance to preventover facilitation. Such a treatmentapproach in the early stages appears tobe more reflective of facilitating achange in the neural control of themuscular system rather than simplystrengthening underlying muscles.

ConclusionThe results of the present studyindicate· that physically active personswith CLBP and radiological diagnosisofspondylolysis or spondylolisthesis,have a different pattern ofabdominalactivation when drawing in theabdominal wall muscles in supinecrook lying, compared with pain freecontrols. It appears that these CLBPsubjects have greater difficulty inpreferentially activating the deepabdominal muscles so as to gain alOmmHg pressure rise on the pressurebiofeedback monitor during thismanoeuvre, and tend to compensatefor this by activating higher levels ofupperRA..Given the importance of thedeep abdominal muscles in theprovision·of dynamic stability to thelumbar spine, and the limited ability ofRA in this regard, this finding mayindicate a dysfunction in theneuromuscular system's ability toprovide dynamic stability to the lumbarspine. This finding is particularlysignificant in the CLBP populationinvestigated, where the passive stabilityof the anatomical restraints to motionwere compromised.

ORIGINAL ARTIClE AUSTRAliAN PHYSIOTHERAPY

from Page 91AcknowledgementsThe authors wish to thank Brigitte vander Heide for her assistance duringsubject testing and Toby Hall for histechnical assistance.

Footnotet - pressure biofeedback monitor ...Chattanooga AustraliaPty Ltd,Queensland

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