AUSTRAliAN PHYSIOTHERAPY

Garry AllisonKevin SingerRobert arshall

ORIGINAL ARTICLE

Muscle activation patternsduring transfers in individualswith spinal cordinlury

The utility of functional electrical stimulationregimens depend on an understanding ofmovement strategies and muscle activationpatterns. The purpose of this study was todescribe the electromyographic{EMG) profilesof the lateral transfer in individuals withspinalcord injury. Two movement strategy groupswere examined: translatory (n =9) and rotatory(n =4). Transfer event markers were identifiedfrom force platform data.EMG signal profiles(1 OOmsHoot MeanSquareenvelopes) oftricepsand latissimus dorsi bilaterally were generatedfor each group,. Rotatory movement strategydemonstrates greater muscle synchronisationthan do individuals who translate. The resultsprovide evidence of different phasiccharacteristics of muscle activity during thelateral transfer using two possible movementstrategies. The implications for interventionregimens are discussed.[Allison G, Singer K and Marshall R: Muscleactivation patterns during transfers in individualswith spinal cord injury. Australian Journal ofPhysiotherapy 41: 169-176]

Key words: ElectricStimulation; Electromyography;Movement; Spinal Cord Injuries

GT Allison PhD BEd(Hons), MEdBAppSc{Hons)is a lecturer at the School of ·Physiotherapy,Curtin University of Technology, Perth.

KP Singer PhD is Associate Professor at theSchool of Physiotherapy, Curtin University ofTechnology, Perth.

RN Marshall PhD is Associate Professor in theDepartment of Human Movement at TheUniversity of Western Australia.

Correspondence: GT Allison, School ofPhysiotherapy, Curtin University, Selby Street,Shenton Parkl Western Australia 6008.

uadriplegia is a conditionaffecting all four limbs, which isinvariably caused by a high level

lesion of the spinal cord. It is asignificant life threatening incidentwhich has major motor, sensory andpsychosocial consequences (Bromley1986). The ability of patients mthquadriplegia to perform simpletransfers successfully is a majorrehabilitation goaL The ability totransfer allows the individual to reachfunctional independence duringactivities of daily living (ADL) withincreased opportunities for socialinteraction outside the rehabilitationinstitution (Bromley 1986, Norris­Baker etaI1981).

The most common transfertechnique is the sitting transfer wherean individual transfers laterally from

"one surface to another while in asitting posture. In wheelchair users, ithas been estimated that about 70 percent of all transfers are of this type(Platts 1971) and, in .paraplegicwheelchair users, an average of 14 to18 transfers are performed each day(Pentland 1992). Transfers are a majorcomponent of functional indicesassociated with mobility andindependence of individuals withquadriplegia (Gresham et al 1986).

The ability to transfer, in theindividual with quadriplegia, is relatedto the ability to lift the body clear of asupporting surface (Bergstrom et al1985), although some individuals areable to transfer with little clearanceusing sliding boards (Kogi et al 1981).This is particularly true for individualswith weak elbow extension.

Furthermore, it has recently beenreported that at least two movementstrategies may be employed whenattempting to transfer (Allison et al inpress). The first is translatory, wherethe movement of the head and pelvisoccur in the same direction. Thesecond is rotatory, where the head andpelvis move in opposite directions.

Irrespective of the movement strategyadopted by the individual,rehabilitation following quadriplegia iscomplicated, long-term and variedaccording to the level of the lesion andneurological deficits, and may involvemany health professionals, techniquesand modalities (Ford etal 1987, Hill1986, Nixon 1985, Schneider 1985).There are few direct interventions toimprove specifically the ability totransfer in individuals withquadriplegia. Increasing the strength ofthe elbow extensors using posteriordeltoid muscle transfer (Gellman 1991,Moberg 1975 and 1990) and functionalelectrical stimulation (FES) training ofthe triceps muscle (Seeger etal 1989)have yet to be shown to improve theability to transfer.

Functional electrical stimulation forstanding and gait in individuals withSCI has been widely reported in theliterature (Kralj et al1989,Phillips1991). Such programs are based on theanalysis ofthe muscle activity derivedfrom electromyography (EMG) signalprofiles andbiomechanical models ofnormal movement patterns. Similaranalyses are yet to be established forthe lateral transfer in individuals withspinal cord injury (SeI).Therefore the

~

ORIGINAl ARTIClE AUSTRAliAN PHYSIOTHERAPY

Direction of Transfer

figure 1.Schematic representation of two movementstrategies for the lateral transfer inindividuals with SCI as viewed from the P...Aperspective A - translatory where the headand pelvis move in the same direction, B ... rotatory where the head and pelvis move inopposite directions (Adapted from Allisonetal in press).

B Rotatory

Head Movement

--

MethodsSubiect recruitmentFrom a larger study of the motionanalysis of the lateral transfer inindividuals with SCI, 13 subjects wereidentified as performing one of twomovement strategies. Nine subjectsused a translatory movement patternand four subjects utilised a rotatory

level SCI (Allisonet al in press). Incomparison, indiviclualswith lowerlesions and stronger elbow extensionare able to utilise these muscles asprime movers and consequentlyperform a translatory movementpattern when transferring (Nixon1985,Somers 1992). The EMG signalprofiles ofthe different movementbehaviours have yet to be reported.

The purpose of this study was toexamine the phasic characteristics andthe level of synchronisation betweenthe elbow extensors and shoulderdepressors during the lateral transfer inindividuals with SCI who performeither a rotatory or translatorymovement pattern.

Head Movementliliiii

A Translatory

force required to transfer, nor does itaccount for patients who can transferwithout a functioning triceps brachii(McGee et al 1977). Therefore thephysiotherapist must use variedrehabilitation techniques to achievesuccess (Ford et a11987, Kogi et al1981, Schneider 1985). Theidea ofuSIng FESwith individuals with SCI toassist in their functional mobility is notnew. However, the useofFES for thelateral transfer is limited by poorunderstanding of the task,· and morespecifically the muscle activity duringthe transfer.

Individuals with SCI also learn tomodify their motor behaviour to bestsuit their physical capacities. Forexample, during rehabilitation manyindividuals with quadriplegia at theC5and C6 levels learn to substitutemuscles for specific actions and tomaximise angular momentum andmoment arms. The use of a rotatorystrategy involving the alternatemovement of the head and hips hasbeen identified as a possible significantfactor in the relearning of motorpatterns by individuals with higher

from Page 169analysis of muscle activity during thetransfer may provide fundamentalinformation for future interventionssuch asFES.

Electrical stimulation may provideimproved function when the method ofmuscle stimulation replicates themuscle activity pattern ofthefunctional task.·This is achieved byestablishing the phasic or temporalchanges in amplitude of the muscleactivity during· the functional task. Forexample, a neuroprosthesis forprehension has been utilised toimprove function by replicating thefunctional muscle actions (Keith et al1988). Similarly, the phasiccharacteristics of theEMG signalduring stationary cycling have beenused as the basis for synchronisation ofmuscles during electrical stimulationtraining programs with SCI individuals(Phillips 1991).

The phasic EMG signalcharacteristics ofmuscles used duringthe lateral transfer have yet to bereported. However, it would seem thatsuch information may indicaterecruitment strategies of the respectivemuscles during a transfer which wouldserve to develop any FESbasedinterventions.

Factors which predict the ability totransfer have yet to be fully elucidated.However, it is generally accepted thatpatients with quadriplegia must learnto use skills of momentum andleverage, and re-learnkinaestheticawareness, in order to achieve mobilityin bed and the ability to transfer(Buchanan etal 1987, Schneider 1985).It is clear that the optimal performanceof an individual with SCI is dependenton the selection ofspecific movementstrategies and these in turn aredependent on the physical attributesthat remain following the injury. Amain focus on the ability to transferhas been associated with elbowextension strength. For example,Welch et.al (1986) reported that thestrength of the triceps brachiimusclesis critical in predicting the ability of aquadriplegic patient to transfer whilstin the long sitting position. However,this does not quantify the amount of

AUSTRAliAN PHYSIOTHERAPY ORIGINAL ARTICLE

Quietsitting

Pre-transferadjustments

Dynamic Phase e-balancingPhase

Quietsitting

---------aa-;.......------~ .._4III.-.. .......---~--------------~_......,...._4III.............----1~.... -----------_...-....

Transfer Transfer Peak Fz TransferBegining Start Finish

to t1 t2 t3

33 Data points 100 Data points 1.33 Data pOints.I..-----~--~ __ .' __ . . .. •

Time normalisation

figure 2.A time line description of the lateral transfer showing the event markers and time normalisation procedures used to synchronise theEMGsignal profiles.

pattern. The classifications of themovement patterns have beenpreviously defined (Allison et al inpress) and are schematically describedin Figure 1. All subjects were malevolunteers who provided informedconsent and had motor completeinjuries (Frankel Grade A, Band C,Frankel etaI1969). Gender was not aninclusion criteria. Subjects wereincluded if they used a wheelchair forfunctional mobility tasks, were able tosustain a long sitting position safelyand independendy, were willing andable to sit on a hard surface for aperiod of 1ominutes and had beendischarged as an inpatient from theirrehabilitation institution.

Subjects were excluded from thestudy if they were:

i) individuals who had concomitanthead injuries and lor neurologicaldeficits associated with movementdisorders;

ii) individuals who had neurologicalor musculoskeletal disorders priorto or independently of the spinalcord injury; or

iii) individuals with respiratorydistress or illness, decubitus ulcersor upper limb pain that affectedtheir functional mobility.

Ethical clearance was obtained fromThe University of·Western Australiaand Curtin University of Technology.Apart from the availability of a taxivoucher for those who did not havetheir own transport, no financialassistance or inducements wereprovided.

EquipmentTwoEMG amplifier systems wereused in this study. The first was aGrass® instruments amplifier with aGrass® regulated power supplyt. Thesecond was a preamplified system withan Oxford Metrics® interface Ullit§and Motion Control® preamplifiers lJI ,

The preamplifiers had a commonmode rejection rate between 102 and104 dB for frequencies between 60 and1000Hz, 3 decibel cut-off bandwidthat 8Hz and 36kHz, a IMQDC inputimpedance and a gain of 313 at 500Hz.

Both preamplified and normalelectrodes were·used in the study. Ineither case, the electrodes were placedbilaterally on latissimus dorsi as itreflects laterally around the inferiorangle of the scapula and thelongitudinal fibres of the long head oftriceps brachii.Palpationof.themusclebellies was performed with voluntaryresisted muscle action. VVhen the

manual muscle testing demonstrated aweakness, the electrodes were carefullyplaced over the muscle by palpationand the use ofanatomical landmarks.

VVhenpreamplified electrodes werenot used, 3M Ag/Agel disposableelectrodes were used at an inter­electrode distance of 20mm. A bipolarconfiguration with a common earthelectrode on the acromion process wasused and the skin prepared to maintainskin·impedance less than SkQ. Thedifferential amplifiers used in thisstudy were high impedance of greaterthan IMQ with high pass and low passcut-off frequencies set at 3Hz and1000Hz respectively.

Assessment of thelateral transferEach subject was directed, whensignalled, to transfer with his normaltechnique and pace, using only onemovement. For this study, all subjectstransferred to their left.

Mer a familiarisation period,a seriesof transfers was performed. Trials wereexcluded from the study if theindividual lost balance during the task,if he walked his hands along the forceplate during the transfer or if he

ORIGINAL ARTICLE AUSTRAliAN PHYSIOTHERAPY

figure 3.Mean and one standard deviation above the mean of the EMG signal during a lateraltransfer to the left for the triceps and latissimus dorsi biiateraU\,. A. Subjects whoperformed the translatory movement pattern (11 =9). B" Subjects who performed therotatory mO\fement pattern (n= 4). The data have been amplitude normalised to ensemblemean RMS (100ms), and the dynamic phase time normalised to 100 data points. :indicatesthe peak activity during the dynamic phase.

Dynamic Phase ofthe Transfer

o 100

(B) Rotatory Pattern

I···· •..........•.. ··•·•···•··.····.·••b/ J

.~I·.~~~r~~~~})·

period. The mean and standarddeviation for each of the 166 datapoints were calculated for eachmovement strategy group. Themaximum amplitude of the meanEMG signal was defined as peakmuscle activity. The standard deviationwas representative of the variation ofthe time normalised EMG signalbetween individuals.

Table 1 describes mean and standarddeviation of the sample population,lesion level, age, weight and years sinceinjury.

Results

1

2

Dynamic Phase ofthe Transfer

o a--_.&.O.........~~~~~io;,;;;,;l.&.'0-0--

(A) Translatory Pattern

1

C) 0 L----..~~~~4r----.....

~'1j2

Q)

.;a 1.........:mE0 ....-----~...........~............~.......------­oZ 2

QJPtj::i 1~

-,.-04.........:

~ 0 t--iI--.....................~...................... --

<2

population may compromise the safetyof the individuals and, if not, presentsas a logistic dilemma in the clinicalsetting. As the purpose of this studywas to determine the relative muscleactivity over time (phasiccharacteristics) of the identifiedmuscles, the mean RMS of theensemble (trial) average was used tonormalise each EMG signal linearenvelop.

The amplitude normalised EMGsignal linear envelopes were timenormalised to 100 data points duringthe dynamic phase of the transfer and33 data points before and after this

from Page 111performed more than one distinctmovement or made more than oneattempt.

The transfer was performed in thelong sitting position using two forceplatforms as the supporting surfaces.The force platform data were used toestablish event markers for the lateraltransfer. These were used for thesynchronisation and timenormalisation of the trials to establishmean EMG signal profiles. The startof the dynamic phase of the transfer(Tl) was defined as the time when theCentre of Pressure (COP) wasdisplaced 2cm from the static pre­transfer position. The finish of thedynamic phase of the transfer (T2) wasdefined by the peak vertical (Fz) forcewhich was associated with theplacement of the pelvis onto thesupporting surface. The EMG signaldata 'were collected during a periodbefore, during and after the dynamicphase. The beginning of the datacollection (TO) and the end of the datacollection (T3) were defined as onethird of the duration of the dynamicphase of the transfer (Figure 2).

Data reduction

Three trials were recorded at 500Hz.The data were initially demeaned andfull wave rectified. Digital filtering wasperformed on the EMG data toattenuate the amplitude of signals withfrequencies below 6Hz using a fourthorder zero-phase lag Butterworthdigital filter (Winter 1990). These datawere then smoothed using a RootMean Square (RMS) over 100ms. Thisprovided a linear envelope of the EMGsignal.

Amplitude normalisation

It is recognised that assessment of themuscle activity using the EMG signalduring functional tasks is related to thetype of muscle action that is performed(Allison et al 1993). Amplitudenormalisation using maximal voluntaryisometric contractions in generalincreases the variance in the groupeddata. Moreover, attempting maximalcontractions in the muscles crossingthe shoulder girdle in the SCI

AUSTRAlIAN PHYSIOTHERAPY ORIGINAl ARTIClE

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Figure 3 shows the EMG signaltemplates of the four muscles testedduring the lateral transfer. The rightand left are defined as viewed frombehind. All subjects transferred to theirleft (see Figure 1). These templatesshow the mean and one standarddeviation above the mean of the ninesubjects who performed the translatorymovement pattern (Figure 3A) andfour subjects who performed therotatory movement pattern (Figure3B). The data were time normalisedwith the dynamic phase of the transfer(shaded) representing 100 data points.

Figure 3 also illustrates the peakactivity of the average EMG signal forall muscles during the transfer. Duringthe translatory movement strategy, theright triceps and latissimus dorsireached peak activity in the first 25 percent of the dynamic phase of thetransfer. In the corresponding leftsided muscles, peak activity occurred atapproximately 75 per cent of the timenormalised transfer. In comparison,the rotatory transfer demonstrated thatthe peak activity of all the musclesoccurred at approximately 60 per centof the dynamic phase of the transfer.

The peak activity of both elbowextensors and the right latissimus dorsiappear to be synchronised. Thereforethe degree of simultaneous peakactivity of the muscles on each side ofthe body during the rotatory pattern isgreater than those in the translatorypattern.

DiscussionEMG signal profiles were used toassess muscle activity during twopatterns of lateral transfers performed

~

from Page 173by individuals with SCI. The findingssuggest that phasic activity of thetriceps and latissimus dorsi are not asdefinitive as the phasic nature of thelower extremity muscles during gait(Perry 1992). However, in bothmovement strategies there seems to bea level of simultaneous activationbetween the elbow extensors and thelatissimus dorsi on the transfer (right)side. Indeed, both groupsdemonstrated increased muscle activityduring the dynamic phase of thetransfer, which would indicate that theevent markers delineated the liftingphase of the transfer.

In individuals who performed thetranslatory movement pattern, thepeak activity of the right triceps andright latissimus dorsi· occurred atsimilar times during the first half of thedynamic phase of the transfer. Theamplitude of the EMGsignal thengradually decreased throughout theremaining phase of the transfer. Theincreased amplitude of the EMG signalat the early stage of the dynamic phaseof the transfer may be associated withconcentric muscle actions (Allison etal1993, Komi 1992, White et aI1993).Therefore, the level of activity of thesetwo muscles seems to be synchronisedand indicates that they may be actingas prime movers or agonists. This isfurther supported by the fact that allthe individuals who performed thetranslatory movement strategy hadlesions at or belowC7 and thereforehad relatively strong triceps whencompared with individuals with higherlesions. The left triceps and latissimusdorsi reached peak activity in the latterhalf of the dynamic phase of thetransfer. However, the activity patternof the left latissimus dorsi is less clearsince there was little amplitude changein the average signal during thedynamic phase of the transfer. Thismay imply that there were only smallchanges in the level activation of thismuscle during the dynamic phase ofthe lateral transfer (ieminimal phasicresponses) or, if subjects diddemonstrate phasic responses, thatthere was little synchrony betweensubjects. In the latter case, the

ORtG I N ALAR TIe t E

variation may reflect the diversity ofmotor behaviours of the individualsand/or the functional diversity of themuscle during the transfer, since theEMG signal amplitude may vary dueto the load and the type of muscleactivity (Komiet a11987, White et al1993).

Similarly, the left latissimus dorsi inindividuals who transferred using therotatory method was found todemonstrate minimal phasiccharacteristics. Therefore, the motorpattern·of the left latissimus dorsi (theplacement arm) illustrates minimalphasic responses during the dynamicphase of the transfer, irrespective ofthe movement strategy adopted by··theindividual.

The time of the peak activity of theelbow extensors was different betweenthe rotatory and translatory movementstrategies. During the translatorymovement strategy, the right tricepsreached the peak activity in the first 25per cent of the dynamic phase whereasthe left triceps peaked in the last 25 percent of the transfer. This unilateralsynchronisation may reflect thefunction of the muscles acting as primemovers. Consequently, a bilateralsynchronisation may be required tomaximise the rigidity and rotation ofthe trunk. In summary, these findingsdemonstrate different muscle activitypatterns during the two movementstrategies when transferring.

Rehabilitation implicationsThe nine individuals who performedthe translatory movement pattern hadlesions at or below C7 (Frankel A,B orC).Consequently,they had relativelystrong triceps and latissimus dorsi. Theindividuals who performed the rotatorypattern had higher lesions and hadweakness in voluntary elbow extension.These two patterns imply that themovement strategy for any futureFESinterventions ·may vary and factorssuch as anthropometric parametersmay influence the strategy selectionbest suited to the individuaL Thereforethis study supports the notion thatmotor learning and motor behaviourscan not be overlooked during therehabilitation phases, particularly if

AUSTRAlIAN PHYSIOTHERAPY

electrical stimulation programs are tobe attempted (Buchanan et al 1987,Ford et al 1987, Schneider 1985).

The findings of this study raiseanother issue for physiotherapistsconsidering a FES rehabilitationregimen,specifically the type ofelectrical stimulation protocol that maybe attempted. Two approaches may betaken when using electrical stimulationto improve function. The firsttechnique involves the use of electricalstimulation to replicate the muscleactivation patterns which result in anear to normal muscle firing sequence.The second is a simpler approachwhich uses electrical stimulation as amethod of assistance either to facilitatemuscle function or, in conjunctionwith an assistive orthotic device, as ahybrid gait training system. In thecontext of this study, it would seemthat to replicate a translatorymovement pattern, at least two phasesof stimulation are required, where theleft and right sides are stimulated insequence.

To replicate the rotatory strategymuscle function,all the muscles maybe stimulated essentiallysimultaneously. However, the smallsample size limits furthergeneralisations. Nevertheless, the useof FES to assist transfers other thanreplicating the muscle activities foundin this study is an issue for futureresearch, particularly when consideringpossible hybrid/orthotic devices as intheFES-Reciprocal-Gait Orthosis(Phillips 1991).

The replication of muscle activitypatterns, as in gait, requiresstimulation control parameters whichmodulate the level of torque. generatedby the contracting muscle andminimise the effects of fatigue.Although the EMG signal profiles ofthis study provide·some information asto the phasic responses of the muscleactivity, further investigation of themagnitude of the muscle's activityduring the transfer is needed, sinceamplitude is dependent on the level ofthe contraction, the action and velocityof the muscle (White etal 1993). Inthis study, both muscle groups acted

AUSTRAliAN PHYSIOTHERAPY

across multiple joints, and it wouldseem that they may act in varyingdegrees as stabilisers as well as primemovers, according to the movementstrategy. The left latissimus dorsidemonstrated minimal amplitudechanges of the EMG signal during thetransfer compared with the othermuscles, irrespective of the movementstrategy. Further analysis is required toelucidate the torque requirements andcontrol parameters of a FES programto achieve a successful transfermovement pattern.

During the lateral transfer, fatigueinduced by repetition may not be amajor problem, since the task is ofshort duration. However, fatiguerelative to the level of torque requiredmay be critical. The reason for this isthat the muscles targeted in FEStraining for transfers are likely to bepartially·innervated, since the zone ofinjury may affect the final commonpathway ofsome of the motor unitswithin the muscle. Therefore, themuscles may require maximalstimulation to generate sufficienttorque for a transfer. Clearly, asdemonstrated byFESgait programs, astrength training regimen would needto precedeFES applications (Phillips1991).

Moberg (1975) estimated the forcesat the wrist required to achieve atransfer to be as small as 7kg. Althoughit is possible to generate significantelbow extension torques in normalmuscles, there are three factors whichneed consideration during electricalstimulation interventions in individualswith quadriplegia. First, the finalcommon pathway to the muscle mustbe intact (upper motor neurone lesion)to allow sufficient stimulationfrequencies to generate significanttorques. Secondly, it is yet to bedemonstrated if an electricalstimulation training program cangenerate sufficient torques for atransfer in both triceps and latissimusdorsi. Finally, iEthe latissimus dorsi or,more importantly, the triceps brachii,can be stimulated to generatesignificant torques, then the zone ofinjury.must be proximal to theinnervation level of these muscles. In

ORIGINAl A RTIC l E

such cases it may be questionable if thevoluntary muscle control at theshoulder girdle is sufficient to provideadequate proximal stability duringtransferring tasks, irrespective of themovement strategy. These issuesremain unanswered.

ConclusionsThis study demonstrates the phasiccharacteristics offour muscles in twogroups of individuals with SCI who usedifferentmovement strategies whenattempting to transfer. Relativesynchronisation of the peak muscleactivity during the dynamic phase ofthe transfer differs according to themovement strategy selected by theindividual. These EMG signaltemplates may direct futurebiomechanical and kinematic researchand development ofrehabilitationintervention programs, such as FES,which could facilitate the ability totransfer in individuals with high to midlevel quadriplegia.

Footnotest Grass Instrument Co., Model P511K, RPS

l07CQuincy, MAUSA.

§ Oxford Metric Ltd. Model VC082 0 Oxford,England.

-n Motion Control, Division of IOMED Inc.Salt Lake City, Utah USA.

AcknowledgementsThe authors would like toacknowledge the assistance providedby the technicians from TheUniversity of Western AustraliaDepartment of Human Movement.

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