AUSTRAllAN PHYSIOTHERAPY

Sonia t&,,§1l!~""m.ft.\'Hl'

~Jenkins

Smith

o RIG I NA L ARTie l E

Rate and force of applicationof manual chest percussionbyphysiotherapists

The rate and force of manual chest percussionas applied by 35 physiotherapists wasinvestigated. The influence of gender, bodyweight, body mass index {BMI}, rate andfrequency of usage on force were examined.Percussion was applied to ahealthy male for 35seconds and the rate and force were measuredusinga force platform. The rate andforcevariedamong subjects. The mean (SO) rate and forceof percussion were 6.60 (1.00) Hertz and 58.10(15.32) Newtons respectively. There was norelationship between force and 1) gender, 2)bodyweight, 3)BMI or 4) frequency of usage ofpercussion. A weak relationship was foundbetween rate and force (r= -0.358, p=0.034).Thirty-two subjects demonstrated a handdominance.[Slazey SM,Jenkins SC and Smith RA: Rate andforce of application of manual chest percussionby physiotherapists. Australian Journal ofPhysiotherapy 44: 257-264]

Key words: AirwayObstruction; lung Diseases;Percussion

SM Siazey SSe (Phty)(Hons) was anundergraduate student a,t the School ofPhysiotherapy, Curtin Universityof Technology,Perth at the time of this study and is now aphysiotherapistatFremantleHospitaI, WesternAustralia.SCJenkinsPhD, GradOipPhty Isa senior lecturerin the School of Physiotherapy at CurtinUniversity of Technology, Perth.

RASmith BSc(PGDip) is aresearch assistant inthe School of Physiotherapy at Curtin Universityof Technology, Perth.

anual chest percussion is one ofmany techniques used incardiopulmonary physiotherapy

to promote airway clearance (Stillerand McEvoy 1990). Percussion is adownward force applied rhythmicallyto the patient's thorax over theinvolved segment(s) of the lung. It issuggested that the compression oEairbeneath the cupped hands creates anenergy wave which is transmittedthrough the chest wall to the airways.This theoretically loosens bronchialsecretions, thereby promoting airwayclearance (Shapiro et al 1991). Therate and force at which percussion isapplied may influence treatmentefficacy.

Studies involving percussion haveused different rates and these havebeen recorded in Hertz (Hz), beats perminute, cycles per minute, times perminute and strokes per minute. Inorder to be consistent, in the followingdiscussion, rates have been convertedto Hz, where 1Hz is equal to one clapper second. The reported rates instudies involving percussion (asperformed by physiotherapists on adultpatients) have ranged from 0.1 to 8Hz.

Correspondence: Sonia Blazey, PhysiotherapyDepartment, Fremantle Hospital, Alma Street,Fremantle, WA 6160. E-mail:sonia.blazey@health.wa.gov.au

This paper was presented at the NationalCardiothoracic Conference in Perth, WesternAustralia, in October 1997.

Although no published studies havemeasured the rate and force ofpercussion applied to human subjects,recommendations for the technique ofpercussion have been made by severalauthors. Gallon (1991) found thatsputum was cleared more rapidly withfast manual percussion (8Hz) than slowmanual percussion (0.1 to O.2Hz)which suggests that the rate ofpercussion may influence the rate ofsputum expectoration. lmle (1989)reports that percussion is performed at1.7 to 8Hz, whilst other authors claimthat percussion .is applied at a rate ofapproximately 5Hz (Pavia 1990, Suttonet al 1985). In published research,percussion has been performed at 0.1to O.2Hzand 8Hz (Gallon 1991),JHz(vander Schans et al 1986) and 5Hz(Bateman et al 1979). These reportedvalues are oflittle relevance if the ratesat which physiotherapists normallyapply percussion are not known. Zadai(1981) suggests that percussion shouldbe applied with sufficient force todislodge secretions without causingpain. Other authors state that theeffectiveness of percussion is notrelated to its foreeof application(Certo 1993, Frownfelter 1987).However, all three authors failed toprovide any data to support theirstatements.

There is only one published study inwhich the inherent rate and force ofpercussion applied by physiotherapistswas measured (Flower etal 1979). Theresearchers used- a simulated chestcomprised of a curved block, placed ona transducer. The simulated chest was

percussedby physiotherapists and theoutput from the transducer recorded.The output was analysed for the rateand force .ofpercussion.Physiotherapists working exclusively incardiopulmonary care percussed at arateof7.5 to 8.0Hz, whilst those withother duties utilised arate of 4.2 to6.0Hz. The force ranged from 58 to 65Newtons (N) and it is interesting tonote that this is a small range.

To date, there have been no studieswhich have examined the effect of theforce of percussion on treatmentefficacy or whether factors such asgender, body weight, body mass index(BM!) or the frequency of usage ofpercussion are related to force. Beforethe effect of rate and force ontreatment efficacy can be established, itis necessary to determine the inherentrate and force of percussion as appliedby physiotherapists. These data wouldalso he valuable in the criticalevaluation of published research. It isimportant for the force of percussionto be determined to ensure the safetyof the technique and also for medico,;..legal reasons, should a rib fractureoccur during a physiotherapytreatrnentwhich includes percussion.The present study investigated the

rate and force of percussion as appliedby physiotherapists to a human chest.In addition, the effect of gender, bodyweight, BMI, rate and frequency ofusage of percussion on force wasexamined.

MethodA descriptive, correlational and quasi­experimental study design was used.The study was approved by the HumanResearch Ethics Committee of CurtinUniversity ofTechnology: All subjectsand the patient model gave writteninformed consent prior toparticipation.

SubiectsThe subjects consisted ofa volunteerpopulation of qualifiedphysiotherapists. Subjects.wererecruited using the following methods:1) an advertisement was placed in theAustralian Physiotherapy Association

ORIGINAl ARTIClE

WABranch newsletter. Thisadvertisement was also distributed topostgraduate cardiopulmonarystudents and displayed fnthe School ofPhysiotherapy at Curtin University ofTechnology; 2) a letter was sent to the1993 and 1994 physiotherapygraduates from·Curtin University,encouraging participation in the study;and 3) the study was described duringstaff meetings at three major adultgeneral hospitals in Perth. Subjectswere excluded from the study if auyofthe following applied: 1) the subjectworked exclusively with neonates orpaediatric patients aged less than 10years; 2) presence ofa medicalcondition involving the upper limbs,cervical or thoracic spine; and 3) thesubject had not performedperclissionduring the last four years.

Instrumentation andexperimental setup

The AMTI (Advanced MedicalTechnology Inc.) BiomechanicsPlatform (force platform) was used tomeasure the rate and force ofpercussion. The force platform consistsof a large plate and a small plate placedside by side within the floor ofthegymnasium at the School ofPhysiotherapy. A plinth was mountedon the force platform such that all fourlegs were in contact with the platform.Percussion was performed on a patientmod~l, a healthy male aged 49 years,who was a non,;..smokerwith normallung function. The patient model waspositioned on the plinth in right side­lying with one pillow under the headand one between the knees. Allclothing above the waist was removedand one layer of towelling was placedover the lateral basal segment of theleft lung. The position of the plinth onthe force platform and the patientmodel on the plinth were marked withsticky labels to ensure standardconditions on each testing occasion. Asthe forces measured in the study werelow relative to the weight of the plinthand patient model, the system waszeroed (manually offset) with thepatient model and plinth on the forceplatform. To improve the resolution,the signal was amplified with a gain of

AUSTRAliAN PHYSIOTHERAPY

4000 and then the digital outputwasincreased by a factor of eight. Thevoltage signal was converted intoNewtons using a calibration matrix.

Pi lot stud iesTwo pilot.studieswere performedprior to the main study.The purpose of the first pilot study

was to calculate the force that would heapplied to the chest of the patientmodel with percussion, but would notbe transmitted to the force platformdue to attenuation by the towel, softtissues ofthe patient model and plinth.A O.235kg rubber weight was placed onthe edge ofa bench which waspositioned next to the force platform.A researcher pushed the weight off thebench with a ruler so that it fellvertically onto the force platform.Components (ie plinth, patient modeland towel) were progressively added onto the force platform and the.weightpushed from a height of 31cm. Theweight fell onto: 1) the small plate ofthe force platform; 2) the large plate ofthe force platform; 3) the plinth; 4) thechest of the patient model; and 5) atowel placed on the chest of the patientmodeL Analysis using a one factorANOVAshowed no significantdifference between the forcemeasurements obtained in the five tests(F(44) =0..80, P=0 .. 532) indicating thatthe'torce attenuation by the variouscomponents was insignificant.

The second pilot study wasundertaken to determine the reliabilityof measurements made using the forceplatform. A plinth was placed on theforce platform and a volunteer waspositioned on the plinth as previouslydescribed. AO.235kg rubber weightwas pushed by the researcher from aheight of 31cm onto the chest 20 timesand the force measured for each triaLThis was repeated seven days later andthe data obtained on the two occasionscompared using an unpaired, two tailedt-test. The first measurement recordedon the first testing occasion wasconsidered to be an outlier and wasexcluded from the analyses. The mean(SD) force was 16.60 (1.35) Nand16.54 (2.J8) Non the first and secondtesting occasion respectively

AUSTRAliAN PHYSIOTHERAPY

(·t = 0 11· P= 0.913). The findings of(37) •. ,

this study.indicated that measurementsmade using the force platform arerepeatable.

ProceduresTesting took place on four afternoonsover a two-week period. Subjectswaited in a room distant from the siteof testing, so that subjects could notinfluence each other in theperformance of~e task. Dem?graphicinformation,detads of professIonalexperience and frequency of usage ofpercussion (defined as the number ofdays per week on which percussion wasperformed) were obta}ned £.romsubjects using a queStI0!lnaire. Thesubject's height and weIght weremeasured and used to calculate theBMI. The task involved the subjectpercussing the left lateral basal lungsegment .of the patient model, thr?ughone layer of towelling, for a duration of35 seconds. This time period waschosen as it approximates the .recommended duration of perCUSSIOP.(W"ebber and Pryor 1993) and.shouldnot result in fatigue ofthe subject orthe patient model. The followinginstructions were provided to allsubjects:

"The patient model has normal lungfunction and a normal thoracic cageand therefore there are.nocontraindications to percussion.Percuss with two hands the lateralbasal lung segment of the patie~t

model using your normal technI9ueuntil I say to stop. Allow the patientmodel to breathe at his normal rateand depth. Do you have anyquestions?"

The force platform was programmedto sample data at a frequencr of,1OOHzand was activated by the subject s firstclap. Percussion was applied d~ring

tidal breathing and not.thoracIcexpansion exercises (TEE) for thefollowing reasons:

• The large respiratory movementsassociated ·with TEE mightinfluence the voltage signalrecorded by the force platform.

• A large number of subje~ts wer~examined on each occasIon. This

ORI G IN A t ARTIClE

would result in repetitive TEE bythe patient model whichn:Ig~tcause fatigue or hyperventilation.

The procedure was videotaped usingaPanasonic F15CCDcameraconnected to a Panasonic ag7330 videorecorder. The video recorder focusedon the chest of the patient model andthe upper limbs of the subject. Thisprovided a secondc~eckof ~e rate ofpercussionhy replayIng the VIdeo,counting. the number of claps andcomparing the counted rate to thatobtained from the force platform. Therecording also provided qualitativedata, thereby allowing description ofthe technique of percussion.

Dotomanagement andstatistical analysesVisual basic programs were written inMicrosoft Excel version 5.0 to analysethe data. The forces measured by thesmall and large plates were added togive a total vertical force. This wasthen filtered to remove the effect ofnoise, defined as components of theraw data which are not due to theprocess being measured .(ie percussion).This added component IS usually ofahighfrequeney (W"inter 1?90). AButterworth 4th orderlow pass digitalfilter smoothed the data by attenuatingall frequencies greater than 20Hz.Data recorded during the first fiveseconds of percussion were no~ .~included in the analyses as durIng thIStime, subjects may be establishin.g therate and rhythm of their perCUSSIon.

For each subject, the rate ofpercussion was determined.Descriptive statistics for the force ofpercussion were calculated forindividual subjects and for the group.An unpaired, two tailedt-test was usedto examine the effect of gender on theforce of percussion. Pearson productmoment correlation coefficients (r)were calculated between: 1) force ofpercussion and body weight; 2) force ofpercussion and BMI;and 3) rate andforce of percussion. A one factorANOVA was used to compare theforce of percussion between thefrequency of usage categories. Acritical alpha (P) value of0.05 was usedto determine statistical significance.

Microsoft ExceIS.O, Statview 4.1(Abacus Concepts Inc.),Statview SEand Graphics 1.04 (Abacus ConceptsInc.) and SuperAnova 1.11 (AbacusConcepts Inc.) were used for dataanalyses.

ResultsThirty-five subjects (30 females)completed the study. The mean (SD)age ofthe subjectswa~29.5 (6.1) years.Thirty-one oEthe subJects (89.6 percent) had graduated from CurtinUniversity. The mean (SD)num?er ofyears sincegraduationofthesubJ~cts

was 7.8 (6.3) years. AnthropometrIcdata for individual subjects and for thegroup are given in Table 1.

Data managementThe waveform of the force producedon the chest wall with percussion wassinusoidal (Figure 1). As the subject'shand contacts the chest wall, amaximum force results. As the hand iswithdrawn, a minimum force occurs.The total force for each clap wasdetermined by calculating thedifference between the maximum andminimum force{eg in Figure l,·themaximum and minimum force for thefirst clap are 28.09 and --27.82Nrespectively, giving a total force of55.91N).

Three patterns were found onexamination of the waveforms(Figure 2).

In Pattern 1 (27 subjects) the handcontacts the chest wall once with eachclap. As the force is applied down ontothe chest, a positive maximum forceresults. As the hand is lifted from thechest recoil of the tissues induces anupwa~d deceleration force,whichexplains the negativ~values for. theminimum force. This occurs WIthevery clap.

In Pattern 2 (four subjects) the handcontacts the chest wall once with eachclap. However, occasi<?nally ~eminimum is not negative, but ISslightly positive. This is due t?the nextclap occurring before a negative forcevalue occurs.

In Pattern 3 (four subjects) the handcontacts the chest wall more than once

ORIGINA-t ARTICLE AUSTRAliAN PHYSIOTHERAPY

Pattern 2

40

30

20

Z 10~ 0 ....---+-+-+----+---++-+--tH-~---...+_+__-r----+_i_"__""iI._......__f_f_~__1

Ll-

S ~IO

,e ~20

-30

-40

Time (5)

Figure 1. The waveform of the force produced with percussionfz ... vertical force; N-Newtons; s -seconds.

figure 2. (right) The three patterns found on examination of thewaveformsfz- vertical force; N - Nevvtons;s - seconds.

figure 3. An example of band dominanceN ... Newtons.

for each clap.. For subjects whose forcetrace conformed to this pattern, thevideo was replayed as slowly aspossible, however it could not bedetermined which part of the hand wascontacting the chest first. The mostlikely explanation is that the ulnar sideof the hand contacts the chest beforethe radial side.

Rate and force of percussionTable 1 gives the rate and force datafor the 35 subjects. The mean (SD)rate of application of percussion was6.60 (1.O) Hz (range, 4.60 ~ 8.47Hz).The mean (SD) force of percussion

was 58.10 (15.32)N(range, 29.54 ­88.75N).

Although the mean (SD) force wasgreater for males (68.25.(18.33) N)than females (56.41 (14.42)N) thedifference was not significant(t(33) =1.639,p :::0.111). There was nosignificant relationship between bodyweight and force (r=O.010,p= 0.954)or BMI and force (r <=-0.177,P =0.313). There was a small, butsignificant relationship between rateand force (r::: -0.358, P=0..034).

For further analysis, subjects weredivided into three groups depending

on the frequency ofusage ofpercussion. Although the forceappeared to increase with thefrequency ofusage ofpercussion(Table 2), the increase was notsignificant (F(Z,3Z) =0.339, p= 0.715)"

Hand dominanceFrom graphical observations, it wasapparent that some subjects produced agreater force with one hand than withthe other. An example of this isdisplayed in Figure J. This observationled to further statistical analyses. Foreach subject, an unpaired, .two tailedt-test was performed to compare the

AUSTRAliAN PHYSIOTHERAPY OR lG 1N A1 ARTie l E

This study demonstrates thatpercussion continues to be used byphysiotherapists, with 60 per cent ofsubjects performing the technique onat least one day per week. There isconsiderable variation in the rate andforce of percussion amongphysiotherapists.

Flower et al (1 979) measured the rateof percussion by physiotherapists,however reported only limited data.The range of rates found in the presentstudy (4.60- 8.47Hz) is similar to thatreported by Flower et al (1979)(4.2-8Hz).

Rates ranging from 0.1 to 8Hz havereportedly been utilised in studiesevaluating airway clearance regimenswhich included percussion (Bateman etal1979, Gallon··1991, van cler Schanset al1986, White and Mawdsley 1983).In one study, a rate of 4.2Hz waschosen and this was regulated by ametronome (White and Mawdsley1983). However,maintaining a set ratewith the use of a metronome is likely

Discussion

force produced by each hand. Asignificant difference in the forceproduced by the right and left handswas present in 32 of the 35 subjects(91.4 per cent). In these 32 subjects themean (SD) difference in force betweenhands was 10.05 (6.3) N (range,1.29-25.9N). In 13 of the 35 subjects(37 percent) the difference in forcebetween hands was less than SN. Forthe 32 subjects the dominant handproduced a mean (SD) of21.0 (16.9)percent.(range, 3.4-71.5 per.cent)more force than the non-dominanthand. Of the 32 subjects .demonstratinga hand dominance with percussion, 26(82.2 per cent) were dominant withtheir preferred writing hand.

Variations in techniqueOn replay of the video it was apparentthat variations in the technique ofpercussion existed. Some subjectspredominantly used the wrists, withvery little elbow movement, whilstothers used varying degrees of elbowflexion and extension when applyingperCUSSIon.

Force(N)

mean SD coefficientofvariation

(%)

1 F 49 18.7 6.90 46.79 6.42 13.72 M 84 27.7 7.77 49.10 14.87 30.33 F 54 19~4 6.73 62.14 5.43 8.74 F 62 23.2 6.83 66.51 12.73 19.15 F 56 20.8 4.70 40~06 4.65 11.66 F 59 19.5 5.07 74.22 8.11 10~9

7 F 62 19.6 6.67 65.18 5~15 7.98 F 58 21.8 4.60 34.72 2•.93 8.49 F 61 20~9 7.83 48.29 11.65 24.1

10 F 60 21.4 5.40 79.32 12.34 15.611 F 90 32.1 8.47 29~54 4.63 15.712 F 46 19.7 5~57 57.80 7.81 1J~5

13 F 80 27.0 6.27 60.59 6.27 10.314 F 56 20.6 6.80 69.60 7•.43 10.715 F 50 20.0 5.70 66.45 6.'57 9.916 F 48 19.2 5..80 8.8.75 7~98 9.017 F 75 25.1 6.67 60.87 7.11 1··1~7

18 F 54 19.6 7.50 31.53 4.88 15.519 F 63 20.3 7.73 50.19 7.42 14.820 F 62 22.8 7.30 49.34 12.09· 24.521 F 59 23.2 7.53 63.01 8.55 13.622 F 61 20.4 5..53 75.03 10.44 13.923 M 83 22.5 6.27 88.68 8.95 10.124 F 55 21.7 6.00 57.61 8.51 14.825 M 77 22.7 6~93 84.24 8.43 10.026 F 51 17.3 6.53 35~66 8.29 23.227 F 64 20.3 6.73 66.36 9.53 14.428 F 57 20.6 8.30 43.35 10.42 24.029 F 62 21 ..3 5.00 62.84 6.32 10.13.0 F 86 29.9 7.80 47~84 6.93 14.53J M 69 23.1 5.97 68.42 8.26 12.132 M 81 21~8 7.17 50.80 7.42 14.633 F 58 20~8 7.30 58.03 8.79 15.134 F 51 19.2 7.13 48.15 12~91 26.835 F 67 23.5 6.53 52.60 11..34 21.6

mean 63.·07 21.93 6.60 58.·10 :>8.33 15::-0···'SD 11.77 3.16 1.00 t5~32 :2/73 5/74

N-NewtollS;kg-ki10gramS;1JAll-b(>dyis~i~I~¢hlse9P~1~6tlte" ""eight I height2 where theweightismeasuredmkilopratllsandtlte::height

\ in metres(m){Garrow 1988);Hz-Hertz;SD-standarddeyiati0n:r»>'<.:::',:-:,».c()efficientofv(lriationrefers to· the standard .deviaUQn>as>ap~rc;e1}tage()f:<:>:fhetnean;%-percent.

ORIGINAl ARTIClE AUSTRAliAN PHYSIOTHERAPY

Tabl.e2~<Thefotceofpercussionbysubjectsine,ach frequency ofusage category

Freq- frequency; Freqofusageofpercussion refers to. the •number.ofdaysper week on which percussion is performed; n-number;N-Newtons;SD·- standard·deviation.

performed on a human chest but on acurved block representing the cheste Inthe present study, percussion wasapplied to a human chest, which ismore relevant to clinical practice.

There is no published research whichhas determined the effect ofthe forceof percussion on treatment efficacy.The present study demonstrates thatthere is a large range in the force ofpercussion as applied by·physiotherapists. Further researchshould be aimed at determining theforce of percussion used in differentpatient populations and the effect offorce on outcome measures such as thevolume or weight of sputumexpectorated, rate of sputumexpectoration, mucociliary transportvelocities, pulmonary function, arterialblood gas tensions and oxygensaturation.

Percussion is contraindicated in thepresence of a rib fracture orosteoporotic bone (Starr 1992,Webber and Pryor 199J)e Manypatients requiring .physiotherapytreatment may have osteoporosis dueto decreased mobility, corticosteroidtherapy, poor nutrition, cigarettesmoking and hypoxaemia (Aris et al1996). There are reports that ribfractures have occurred during manualphysiotherapy techniques (Holsclawand Torcato 1996). Force is onevariable which is important in thefracture threshold. Other factors whichmay be important are the amount ofsoft tissue padding, the angle ofapplication of the force relative to theunderlying tissues, the size of thebones and the bone density. It is

SD

16.40

12e8419.02

mean.(N)

important to consider these factors inthe application of percussion and,should litigation occur, the knownforce of percussion would be valuable.There is no published research whichhas investigated the force required tofracture a human ribe Researchers haveexamined the strength of other bonesin humans and in monkeys and allreport bone failure loads in excess ofthe force of percussion (Beckman andPalmer 1970, Singer eta11995,Wilkinson et al 1991)e However, thesestudies involved a single impact ratherthan a repetitively applied force whichoccurs with percussion. Force dataobtained in the present study can beused to establish whether the force ofpercussion applied repetitively mayfracture normal and osteoporotic ribsin cadavers.

It was anticipated that males wouldproduce a significantly greater forcewith percussion than females becausemales generally have more weightdistributed to .the upper body (Rossand Marfell-Jones 1991}e The failureto demonstrate a difference may be dueto the limited number of males (five)included in the.study. Alternatively, itis possible that although malesinherently percuss with a greater forcethan females, they may modify theirtechnique as a result ofcorrection at anundergraduate level or followingobservation of colleagues in clinicalpractice.

The results demonstrate that there isno relationship between the force ofpercussion and the body weight orBMI of the subject. These results wereunexpected. It may be that the

n

1414

7

FreqofusClgeofpercussion (days/week)

olor230r.l11ore

to be difficult if the rate is differentfrom the physiotherapist's.inherentrate. The accuracy ofthe reported ratemust therefore be questioned. Whiteand Mawdsley (1983) failed to providea rationale for the choice of rate intheir studye In the other studies, it isnot clear whether the rate ofpercussion was chosen prior to·thestudy or whether the rate wasmeasured during the study and thenreported (Bateman et al 1979, Gallon1991, vander Schans et al 1986). If therate was measured during the study,the method of measurement was notdescribed and hence the accuracyshould be questioned.

Percussion has been applied at ratesofOe1 to Oe2Hz (Gallon 1991), 3Hz(van der Schans et al 1986) and 4.2Hz(White and Mawdsley 1983)e Thesevalues are all outside the range in ratefound in the present study, hence theway in which percussion was applied inthese studies may not be representativeof clinical practice. However, thepresent study has established the rateof percussion used by physiotherapistseThis will be valuable in future studiesinvolving percussion, which shouldutilise an average rate.

The optimal rate of percussion hasnot been determined. It has beenreported that rapid percussion mayresult in bronchospasm in patients withhyperreactive airways .(Webber andPryor 1993). Frownfelter (1987) statesthat some physiotherapists believepercussion must be rapid to beeffective. However, Frownfelter (1987)considers slow.percussion to be morebeneficial and better tolerated bypatientse There maybe a rate ofpercussion which optimises airwayvibration and mucociliary clearance.The present study determined therates of application ofpercussion byphysiotherapists and these may be usedin future research to determine theeffect of the rate of percussion ontreatment efficacy.

Floweret al (1979) tneasured theforce of percussion and found a muchsmaller range (58-65N) than we foundeHowever, the clinical relevance of thefindings of Flower et al (1979) must bequestioned as percussion was not

AUSTRAliAN PHYSIOTHERAPY

inherent force of percussion is relatedto body weight and ·BMI. However, asphysiotherapy students, the force maybe corrected by teaching staff. Asecond explanation may be that thephysiotherapist modifies the techniquein order to allow for their bodycomposition. For example, the smallestforce of percussion was measured forSubject 11· who had the highest weight(90kg) andBMI (32.1). On replay ofthe video, it was observed that thissubject predominantly used the wristsin performing the technique, with verylittle elbow movement. In contrast, thegreatest force was produced by Subject16 (weight 48kg, BMI 19.2). By usingmore elbow flexion (close to 90degrees of elbow movement), thissubject used the weight of the forearmsin performing the technique. Hence, itmay be that the variability in force isrelated to technique, rath~r than bodycomposition.

A surprising finding of the presentstudy was that there was a weak butsignificant negative relationshipbetween the rate and force ofpercussion. This may also be the resultof differences in technique. It isreasonable to assume that percussioncan be performed atagreater ratewhen the action is predominantlyperformed by the wrist, as opposed to atechnique using a large range of elbowmovements. However, in usingpredominantly the wrist, the weight ofthe forearm is not utilised and hencethe force may be reduced. As therelationship between the variables wasweak, it is not recommended that onevariable (rate or force) be used as anindicator of the othervariable.

The results suggest that the force ofpercussion is not related to theftequeney of usage of the techniquewhen percussion is limited to aduration of 35 seconds. However, force,qid increase with the frequency of1JSage and this increase may have been,~ignificantwith a larger sample size.lturther studies are required to,investigate whether the frequency of\1sage of percussion can be used as an,indicator of force.

, "The results of the present studyi,~ggest that for most physiotherapists

ORIGINAl ARTIClE

there isa significant difference in theforce producedhy the right and lefthands. A future study may examine theinfluence of the force of percussion ontreatment efficacy. In such a study,percussion should be applied byphysiotherapists who demonstrateminimal hand dominance whenperforming percussion.

The main limitation of this study isthat percussion was performed on aperson with normal lung function anda normal thoracic cage, and thus thefindings should not be generalised topatient populations, as the rate andforce may vary with variables such asthe size of the patient, compliance ofthe thorax and the type of lungpathology. As percussion was appliedfor only 35 seconds it is not knownwhether a decline in the force occursover a treatment session in whichpercussion is applied intermittentlyduring the session. It is possible thatforce may decrease over time inphysiotherapists who performpercussion infrequently.

ConclusionThis study demonstrates that whenpercussion is applied byphysiotherapists to a patient modelwith normal lung function, a widerange in the rate and force ofapplication is present. Some previousstudies involving percussion have~applied the technique at rates whichare not representative of those found inthe present study. The findingsindicate that clinically, and in furtherstudies, the force· ofpercussion shouldnot be predicted from gender, bodyweight, BMI or frequency of usage ofthe ·technique. The rate of percussionshould not be used as an indicator offorce. The foreeaf percussion may berelated to the technique used. Mostphysiotherapists demonstrate a handdominance.

AcknowledgementsThe authors wish to thank thefollowing: the patient model, thephysiotherapists who participated inthe study, Dr Jurgen Sommer for hisstatistical guidance and BeatriceTucker for reviewing the manuscript.

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ORIGINAl ARTIClE AUSTRAliAN PHYSIOTHERAPY