JPediatr(RioJ).2016;92(3):319---322
www.jped.com.br
LETTERS
TO
THE
EDITOR
Vertical
segmental
tetrapolar
bioimpedance
for
excess
body
fat
assessment
in
adolescents
夽,夽夽Bioimpedanciometria
tetrapolar
segmentada
vertical
para
a
avaliac
¸ão
do
excesso
de
gordura
corporal
em
adolescentes
DearEditor,
Volume 91, Issue 6 of the Journal of Pediatrics published an article entitled ‘‘Evaluationof the predictive capacity of vertical segmental tetrapolar bioimpedance for excess weightdetection in adolescents’’.1 The authors aimed to analyze,inasampleofadolescents,thepredictivecapacity ofavertical segmentaltetrapolar bioimpedancedevicein thedetectionofexcessweight,usinghorizontaltetrapolar bioimpedanceasareferencemethod.However,we would liketoaddressafewpointstocontributetothe aforemen-tionedsubject.
Electricalbioimpedanceisatechniqueusedforassessing bodycompositionthatisconsideredtobedouble-indirect,2 asitassumesconceptualpremisesbasedonbiological, phys-ical,andmathematicalprinciples,withregressionequations validatedfromanindirectmethod,mostcommonly hydro-static weighing or dual energy X-ray absorptiometry (DEXA).
In this technique, the guiding principle is the ratio between body water content and amounts of the differ-entbodycomponents,basedonthefindingthatleantissue, which containsa largeamount of water(∼73%)and elec-trolytes,isagoodelectricalconductor.Ontheotherhand, fat tissue,which has a small amount of water, is a poor conductor.3
DOIoforiginalarticle:
http://dx.doi.org/10.1016/j.jped.2015.01.006
夽 Please citethisarticle as:Costa RF, Cyrino ES.Vertical
seg-mentaltetrapolarbioimpedanceforexcessbodyfatassessmentin
adolescents.JPediatr(RioJ).2016;92:319---20.
夽夽StudylinkedtotheDepartmentofPhysicalEducation,
Univer-sidadeEstadualdeLondrina(UEL),Londrina,PR,Brazil.
A substance’s resistance is proportionalto the voltage variationofan electricalcurrent appliedtoit.Therefore, througha tetrapolarsystem, in which two electrodes are attachedtotherighthanddorsumandtwototherightfoot dorsumoftheassessedindividual,thebioimpedancedevice identifiesthelevelsofbodyresistanceandreactancetothe passageofanelectriccurrenttoestimatetotalbodywater, amountofleanbodymass,andfatmass.4
Segmentalbioimpedanceuseisnotnew,havingbeenfirst usedinthe1980s,5basedontheobservationthat85%ofthe totalbodyimpedancewasthesumoftheimpedancesofthe upperandlowerlimbs,althoughthesesegmentsconstitute only35%oftotalbodyvolume.Subsequently,thesegmental bioimpedanceapproachbecameincorporatedintomultiple devices,initiallyonlythroughthemeasurementofthelower limbs,inbioimpedancescales,4andmorerecentlyin tetrap-olarequipment,butstilllackingstudiesthatdemonstrateits validity.
This fact justifies the need for studies to assess the predictive capacity of vertical segmental tetrapolar bioimpedancetoestimatebodyfatindifferentpopulation groupsandagegroups.However,thisisonlypossiblewhen usingatechnique considereda ‘‘goldstandard’’ as refer-ence,suchasDEXA;oreven,inordertoassessthetotalbody water,dilutiontechniqueswithbromideordeuterium, for instance,alwaysfollowedbyadequatestatisticalanalysisof theaforementionedvalidity.6
Basedoncarefulreadingofthemanuscript,somedoubts havearisenregardingthemethodologicaltechniques,which inouropiniondeserveclarificationinordertoallowreaders thatdonothaveaprofoundknowledgeofbodycomposition assessmenttounderstandtheassessmentofthepredictive capacityofbioelectricalimpedanceequipment.
First,theauthorsusedadoubleindirecttechniqueasthe standard todefine excessbodyfat and assess the predic-tivecapacityof anotherdevicemodelofthesamedouble indirecttechnique.In ordertojustify thisprocedure, the authorsstatedthatthehorizontaltetrapolarbioimpedance showed high correlation coefficients compared with the gold standard DEXA device, citing four articles. However, one of them is a systematic review that concluded that bioimpedance is a techniquethat does nothave satisfac-toryvalidity;andnoneoftheotherthreestudiescorrelated thebioimpedancewithDEXA.
Second,theauthorsstatethat‘‘theresistanceand reac-tancevalues wereprovided by Biodynamics® (model 450,
0021-7557/©2016SociedadeBrasileiradePediatria.PublishedbyElsevierEditoraLtda.ThisisanopenaccessarticleundertheCCBY-NC-SA
320 LETTERSTOTHEEDITOR
Biodynamics®, WA, USA)’’ and the percentage of fat was calculatedusingthepredictiveequationsofChumleaetal.; however,thecitedarticleaddressesthepropositionof equa-tions for predicting body mass of elderly patients using anthropometricmeasurements,withnorelationtothe bio-electricalimpedancetechnique.
Third, there are some considerations about the sta-tistical analysis used in the study. The authors did not mentionwhethertheytestedtheassumptionofnormaldata distribution, and used the parametric statistics for data description (mean±standard deviation), comparing the resultsbetweenthegendersusingStudent’st-test. Observ-ing the deviation of some variables, we can assume that theyhadnon-normaldistribution,suchassegmentaltrunk fat(TF%)ingirls(9.59%±8.33%)andboys(16.33%±6.94%), withcoefficientsof variationof 86.9% and42.5%, respec-tively. Therefore, the data should have been shown as medianandinterquartilerange,andthecomparisons per-formed by the Mann---Whitney Utest, when a non-normal distribution was detected. As the aim of the study was to evaluate predictive capacity, the positive and nega-tivepredictivevaluesshouldhavebeengiven.Additionally, thecomparisonbetweenthemean/medianvaluesobtained by the utilized standard and those tested should also be included in the results. A concordance analysis tech-nique,suchaskappa,concordancecorrelationcoefficient, or Bland---Altman plot, should also be used. For a good performanceanalysisofabodycompositionprediction tech-nique, regression analysis (slope and intercept) is usually employed, as well as the calculation of the estimated standarderror(ESE).
Inconclusion,wewanttoemphasizethatthescarcityof studiestotestthevalidityofbioelectricalimpedance equip-ment and itspredictive capacity for fat body assessment inadolescentsoftheBrazilianpopulationdemonstratesthe importanceoftheauthors’concernandtheneedforsuch investigations.However,theabsenceofareferencemethod based on multi-compartment models or a gold standard weakensthestudyconsiderablyandcannotbeoverlooked inthediscussion.Thus,themethodologicalcarementioned
here mustbeobserved inordertoincreasethe qualityof theresults.
Funding
RobertoFernandesdaCostaisaPNPD---CAPESfellow.
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
References
1.NevesFS,LeandroDA,daSilvaFA,NettoMP,OliveiraRM,Candido AP.Evaluationofthepredictivecapacityofverticalsegmental tetrapolarbioimpedanceforexcessweightdetectionin adoles-cents.JPediatr(RioJ).2015;91:551---9.
2.MartinAD,DrinkwaterDT.Variabilityinthemeasuresofbodyfat. Assumptionsortechnique?SportsMed.1991;11:277---88.
3.KushnerRF.Bioelectricalimpedanceanalysis:areviewof princi-plesandapplications.JAmCollNutr.1992;11:199---209.
4.ChumleaWC,SunSS.Biolectricalimpedanceanalysis.In: Heyms-fieldSB, LohmanTG, WangZ, GoingSB,editors.Humanbody composition. 2nd ed. Champaign: Human Kinetics; 2005. p. 79---88.
5.SettleR,FosterK,EpsteinB,MullenJ.Nutritionalassessment: wholebodyimpedanceandbodyfluidcompartments.Nutr Can-cer.1980;2:72---80.
6.SunSS, Chumlea WC.Statistical methods. In: Heymsfield SB, LohmanTG,WangZ,GoingSB,editors.Humanbodycomposition. 2nded.Champaign:HumanKinetics;2005.p.151---60.
RobertoF.Costa∗,EdilsonS.Cyrino
UniversidadeEstadualdeLondrina(UEL),Londrina,PR, Brazil
∗Correspondingauthor.
E-mail:roberto@robertocosta.com.br(R.F.Costa).
