www.journalpulmonology.org
ORIGINAL
ARTICLE
Reference
equation
for
the
incremental
shuttle
walk
test
in
Portuguese
children
and
adolescents
T.
Pinho
a,
C.
Jácome
a,b,
J.
Pinto
a,c,
A.
Marques
a,d,∗aLab3R-RespiratoryResearchandRehabilitationLaboratory,SchoolofHealthSciences,UniversityofAveiro(ESSUA),3810-193 Aveiro,Portugal
bCINTESIS---CenterforHealthTechnologyandServicesResearch,FacultyofMedicine,UniversityofPorto,4200-450Porto, Portugal
cSantaCasadaMisericórdiadeÁgueda,3750-130Águeda,Portugal
dInstituteforResearchinBiomedicine(iBiMED),UniversityofAveiro,3810-193Aveiro,Portugal
Received30August2018;accepted18February2019 Availableonline7May2019
KEYWORDS Cardiorespiratory fitness; Fieldtests; Predictiveequation; Children; Adolescents Abstract
Background: Theincremental shuttlewalk test(ISWT) isoneofthe mostwidelyused field teststoassesscardiorespiratoryfitnessinclinicalandresearchsettings.Referenceequationsto predictISWTdistanceindifferentpopulationsandagecohortshavebeenestablished.However, anequationforthePortuguesepediatricpopulationisnotavailable.Thisstudyaimedtodevelop areferenceequationforpredictingISWTinPortuguesechildrenandadolescents.
Method: Healthychildren andadolescentsagedbetween 5and17 yearsoldwererecruited. Sociodemographic(sex,age),anthropometric(height,weight)andphysicalactivity(Physical ActivityIndex)datawerecollected.Lungfunctionwasassessedthroughspirometryand quadri-ceps muscularstrength throughhand-helddynamometry. TheISWTwas performedtwice. A referenceequationwasestablishedwithamultiplelinearregression.
Results:130(60male;13.66±2.61y)participantswithnormallungfunction(forcedexpiratory volumeinonesecond102.73±15.09%predicted),bodymassindex(BMI)(20.27±3.59kg/m2)
and quadriceps muscular strength (19.75±6.84kgf), completed the assessment. 50.8% (n=66) of the participants were moderately active. Participants walked on average 1165.08±327.19m in the ISWT. Sex, age and BMI were independent contributors to the ISWT, explaining 54% of its variability (p<0.001). The derived reference equation was: ISWT=342.06+(283.07×sex)+(83.61×age)−(22.22×BMI),withfemale=0andmale=1. Conclusion:Sex,ageandBMIwerefoundtobecontributorstotheISWTpredictiveequation forpediatricpopulation,providingasimplereferencetoassesstheircardiorespiratoryfitness. ©2019SociedadePortuguesadePneumologia.PublishedbyElsevierEspa˜na,S.L.U.Thisisan openaccessarticleundertheCCBY-NC-NDlicense (http://creativecommons.org/licenses/by-nc-nd/4.0/).
∗Correspondingauthor.
E-mailaddress:amarques@ua.pt(A.Marques).
https://doi.org/10.1016/j.pulmoe.2019.02.009
2531-0437/©2019SociedadePortuguesadePneumologia.PublishedbyElsevierEspa˜na,S.L.U.ThisisanopenaccessarticleundertheCC BY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
The incremental shuttle walk test (ISWT) was developed bySinghand colleaguesin 1992,withtheaimof evaluat-ingcardiorespiratoryfitnessinadultpatients withchronic obstructivepulmonary disease.1The ISWT is basedonthe
distancewalkedarounda10m courseaccordingto differ-ent speedsdictatedby an audio signal.2 The incremental
natureoftheISWTstressesthecardiopulmonarysystemand generatesaphysiologicalresponsetoexercise,3replicating
inthefield,asimilarresponsetoanincremental cardiopul-monaryexercisetest.2 This testis easy toadminister, not
expensive4,5 andhasbeen foundtobeapredictorof
mor-tality and morbidity in patients with chronic respiratory diseases.6---8 The ISWT hasbeen usedasan outcome
mea-suretoassesstheeffectivenessofinterventionsinavariety ofhealth conditions,agegroups andinboth researchand clinicalsettings.2Nevertheless,itsusetoassess
cardiorespi-ratoryfitnessinthepediatricpopulationhasbeensomewhat limited,mainlyduetotheabsenceofreferencevaluesfor healthychildrenandadolescents.Thesevaluesarecrucial to provide comparative data for those living with a dis-ease.Whilstforadults(from18to90yearsold),anumber ofreferencevaluesandreferenceequationsforpredicting and interpreting ISWT distance areavailable3,9---12;for the
pediatricpopulation, onlyonestudy haspublishedaISWT referenceequation.13Inthisstudy,sex,ageandbodymass
indexwere found tobe predictive factorsfor theISWT.13
However, the study was conducted in children and ado-lescentsfromBrazil,andthe normativevaluesfound may notbedirectlyapplicabletochildrenwithdifferentethnic, environmentalandgeographicalbackgrounds.Thus,thereis aneedtoestablishnormativevaluesgeneratedandverified inthelocalpopulation,compatiblewithitscharacteristics.2
Therefore,theaimofthisstudywastoestablish norma-tivevaluesandareferenceequationforpredictingtheISWT inPortuguesehealthychildrenandadolescents.
Methods
Studydesignandparticipants
A cross-sectional study with healthy children and adoles-centswasconductedbetweenJune 2013andMarch2016. Participantswererecruitedfromtwoschoolsinthecentral regionofPortugal.Ethicalapprovalwasobtainedfromthe EthicsCommitteeoftheResearchUnitofHealthSciencesat theSchoolofNursinginCoimbra,Portugal(P186-10/2013& P246-12/2014).Authorizationtoconductthestudyineach schoolwasobtainedfromtheschoolboards.
Childrenandadolescentswereeligibleif:(i)aged5---17 yearsold;(ii)hadnochronicoracutedisease;(iii) under-stoodthestudyaimsandacceptedtoparticipate.Exclusion criteriaincluded: (i) presenceof neurological impairment or significant cardiopulmonary and/or musculoskeletal disorders and (ii) any other significant contraindication thatcould affectphysical testsperformance. Prior toany datacollection,writteninformedassentwasobtainedfrom children and adolescents and written informed consent from their legal representatives. The aim of the study wasexplainedtolegalrepresentatives,at thetimeof the
signing of consent form and they were asked about the healthstatusoftheirchild,specificallythepresenceofany acuteorchronicdisease.
Datacollectionprocedures
Socio-demographic (sex and age) and anthropometric (weightandheight)datawerefirstcollectedto character-izethe sample. A questionnaire tocharacterize the level ofphysicalactivity wasalsocompleted. Aspirometrytest wasperformedtoensurethatparticipantshadnormallung function.Then,quadricepsmusclestrengthwasmeasured. Finally,twoISWTwereperformed.
Physicalactivitylevel
Physical activity levels were assessed using the Physical Activity Index (PAI).14 The PAI is composed of 5
ques-tionsand theanswers arescored ina Likert scale from1 to 4 points. Final score ranges from 5 to 20 points, and canbedividedinto4categories:sedentary, lightlyactive, moderately active and vigorously active.14 This
question-nairehasbeenvalidatedtothePortuguesepopulation,14,15
demonstrating excellent test-retest reliability (intraclass correlationcoefficient=0.92---0.96) andgoodinternal con-sistency(Cronbach’salpha=0.87).15
Lungfunction
A spirometric test using a portable spirometer (MicroLab 3500, CareFusion, Kent, UK) was performed as rec-ommended by the American Thoracic Society/European Respiratory Society.16 Spirometry is a simple and
non-invasivetestanditisindicatedtoassesshealthstatusbefore vigorousexercisetoidentifythepresenceofrestrictiveor obstructiverespiratoryabnormalities.17
Quadricepsmusclestrength
Quadriceps maximum isometric muscle strength was
assessed using a hand-held dynamometer (Hoggan Micro-FET2MuscleTester,Model7477,ProMedProducts,Atlanta, GA) because it is easy to use and portable.18 During the
test, participants were sitting on a chair, with the knee flexedto90◦,hipflexion90◦ andstraighttrunk.The hand-held dynamometer wasplaced on the anteriorsurface of thedominant leg, proximaltothe ankle (5cmabove lat-eralmalleolus).Allmeasurementsweretakeninkilogramof force(kgf).Eachparticipantperformedatleastonepractice trialtounderstandthemovementandacceptable stabiliza-tion.Then,twotrials,oftensecondscontractioneach,were performed;therewasarestingperiodof60sbetweentrials. Themeanofthe2trialswasconsideredforanalysis.19
Cardiorespiratoryfitness
TheISWTprotocolwasfollowedasdescribedbySinghetal.1
andProbstetal.12 The ISWT is an externallypaced
maxi-malexercise test,controlled bypre-recorded signalsthat commandthewalkingspeed.10Thewalkingspeedincreases
0.17m/seachminute,startingat0.5m/s,untilthe partici-pantcannolongercarryonwiththetest.Inthisstudy,the audiosignalscontinueduntilindividualsreachedtheir max-imaleffort,exceedingthe12levelsofspeedrecommended bySinghetal.1Thisproposedadaptationhasbeenpreviously
usedtopredictISWTreferencevaluesinhealthyindividuals (i.e.,children,adolescentsandadults)12,13andwasneeded
toreachindividualsymptomlimitedmaximalperformance andavoidaceilingeffect,consideringthatparticipantswere healthyandcouldpossiblyreachmorethanthe12thlevelto gettotheirmaximalperformance.12Abriefstandard
expla-nationabout thetest wasprovidedby an audiorecording priortotrial.2Participantswereinstructedtowalkbetween
thetwomarkersatthetimeorderedbyaudiosignalsforas longaspossibleuntiltheyweretoobreathlessorcouldnot achievethedistancewithinthebeeptimetwoconsecutive times.Ifatsomepoint,theylaggedbehindthepacedictated bytheaudio-signal, butfelttheywerenotattheir symp-tomlimitedmaximalperformance,astandardizedwarning wasgivenandrunningwasallowed.12,13TheISWTwas
per-formedtwiceduetotheassociatedlearningeffectandthe bestresultwasconsideredforanalysis.4,20Atleast30minof
restwasprovidedbetweenthetwotests.Thedistance(in meters),thelevelandthenumberofshuttlesachievedwere recorded.Ifthetestwasendedthereasonwasregistered.
To ensure proper participant inclusion and safety dur-ingthestudy,physiologicalresponsestoISWTperformance suchasdyspnea,fatigue,heartrate,peripheraloxygen sat-uration,arterial blood pressureandrespiratory ratewere monitoredbeforeandafter thetwoISWTs.17 Dyspneaand
fatigueweremeasured on themodified Borg Scale.21 The
heartrateandperipheraloxygensaturationweremeasured byapulseoximeter(PULSOX-300i,KonicaMinoltaSensing, Inc., Osaka, Japan) on the non-dominant hand indicator andarterialblood pressurewithablood pressuremonitor (Elite,Medel,Parma,Italy).TheISWTisavalidandreliable testwhenassessingmaximalexercisecapacityinindividuals withchronicrespiratorydiseases.20,22Previousresearchhas
shownthattheISWTisareproducibleandvalidmeasurefor assessingthefunction-limitedaerobiccapacityinchildren withcysticfibrosis(6---16years).23
Statisticalanalysis
Thesample sizefor multiplelinearregressiontoestablish referenceequationswasdeterminedaccordingtothe‘rule of thumb’by Green24:N≥50+8m where N is the sample
size and m is the number of independent variables. As 3 independentvariables wereconsidered, a minimumof 74 participantswererequired.
DatawereanalyzedusingIBMSPSSStatisticsversion24 (SPSS Inc., Chicago, Illinois, IL) and plots were created usingGraphPad Prism 5.01 (GraphPad Software, La Jolla, California).Descriptivestatisticswerefirstappliedto char-acterizethesociodemographicandanthropometricdata,PAI score, lung function and quadriceps muscle strength and theISWT. Thepredicted maximalheart rate (HRmax)for each participantwascalculated according to theformula 206.9−(0.67×age), recommended to reflect the differ-encesinheartrateaccordingtoage.25Thenormalityofdata
distributionwasassessedwithKolmogorov---Smirnovtests.26
The intraclass correlation coefficient (ICC) and Bland---Altman plots were used to assess the relative andabsolutereliabilityofthe ISWT.27 ICCwasinterpreted
asexcellent(>0.75),moderatetogood(0.4---0.75)or poor (<0.4).28
Pearson correlation coefficients (age, weight, height, BMI,% HRmax,physical activity level,quadriceps muscle strength and FEV1% predicted) and point-biserial correla-tion coefficient (sex) were used tomeasure the strength of association between these variables and the distance achievedduringtheISWT.Thesecorrelationstestswereused toselectindependentvariablesforthemultipleregression analysis.
A model of multiple linearregression, usingthe Enter mode, was used to estimate the best predictor model for the ISWT distance. ISWT was the dependent variable andvariableswithsignificantcorrelationswereincludedas independentvariables.The assumptionsof linearity, inde-pendence of errors,homoscedasticity, unusual points and normalityofresidualswereanalyzed.ANOVAandR-squared
(R2)wereusedtoassesstheperformanceofthemodel. Toassessthereliabilityoftheequation,measuredISWT distanceswerecomparedwiththevaluesobtainedfroma previously published equation13 using a paired-samples
t-test.Pearsoncorrelation coefficientandBlandandAltman plotwerealsoused.Thelevelofsignificanceconsideredwas setatp<0.05.
Results
Participants’characteristics
A total of 135 subjects were selected, but 2 had abnor-mal lung function, 2 failed to obtain the signed consent forms from their legal representatives and 1 could not complete the assessment due to lack of time. A total of 130children/adolescentswere recruited(60male) and completedtheassessment.Detailedparticipant character-izationissummarizedinTable1.Participantmeanagewas 13.66±2.61yearsold.MostparticipantshadanormalBMI (n=78;60%)andlungfunction(FEV1=102.73±15.09% pre-dicted). BasedonthePAIscore,50.8% ofthe participants (n=66)weremoderatelyactive.
CharacterizationoftheISWT
This section presents the outcomes of the first, second andbestISWT andtherespectivephysiological responses. The first and second ISWT were not significantly dif-ferent (p=0.171) and were strongly correlated (r=0.93;
p<0.001).Excellentrelativereliabilitywasfoundbetween the two ISWT performed (ICC=0.93; 95% CI 0.90---0.95). Bland---Altmanplotshowednosystematicbias,withamean differenceof−15.5m(95%limitsofagreement−266.5to 235.5) (Fig. 1). The best mean distance achieved during the ISWT was 1165.08±327.19m. Males reached signifi-cantly longerdistances than females (1319.33±359.78 vs 1032.86±225.90;p<0.001)(Table2).
Table1 Characteristicsofthesample(n=130).
Characteristics Total(n=130) Male(n=60) Female(n=70) p-value
Age(years) 13.66±2.61 13.67±2.81 13.66±2.44 0.984 Weight(kg) 53.03±14.71 55.05±15.49 51.31±13.90 0.153 Height(m) 1.60±0.14 1.63±0.16 1.58±0.12 0.036 BMI(kg/m2) 20.27±3.59 20.18±3.09 20.35±3.99 0.804 PAIscore 12.32±3.31 12.57±3.28 12.11±3.34 0.439 FEV1(%predicted) 102.73±15.09 101.70±14.71 103.63±15.48 0.486 FVC(%predicted) 96.03±13.99 95.41±14.27 96.56±13.84 0.655 FEV1/FVC 93.22±12.21 90.64±12.77 95.47±11.32 0.032 QMS(kgf) 19.75±6.84 21.98±7.21 17.78±5.91 <0.001
Dataarepresentedasmean±SD.BMI:bodymassindex;FEV1:forcedexpiratoryvolumeinonesecond;FVC:forcedvitalcapacity;PAI:
PhysicalActivityIndex;QMS:quadricepsmuscularstrength.
Table2 Outcomeparametersofthefirst,secondandbestISWT(n=130).
Parameters FirstISWT SecondISWT p-value BestISWT
Distance(m) 1109.54±323.77 1125.00±341.03 0.171 1165.08±327.19 Numberofshuttles 110.95±32.38 112.48±34.09 0.177 116.48±32.71 Level 12.87±2.26 13.03±2.27 0.058 13.26±2.17 Predyspnea(0---10) 0.13±0.57 0.13±0.42 0.939 0.13±0.48 Postdyspnea(0---10) 5.46±2.13 6.12±2.53 0.001 5.89±2.33 Prefatigue(0---10) 0.19±0.74 0.34±0.87 0.093 0.28±0.88 Postfatigue(0---10) 6.63±2.06 6.69±2.48 0.699 6.68±2.32 PreHR(bpm) 81.10±13.74 --- --- 81.10±13.74 PostHR(bpm) 124.49±33.07 125.85±34.56 0.603 125.84±34.42
PostHR(%HRmax pred) 62.90±16.74 63.61±17.58 0.592 63.65±17.48
PreSpO2(%) 97.76±1.65 --- --- 97.76±1.65
PostSpO2(%) 95.95±2.81 95.66±2.87 0.241 95.41±3.59
Dataarepresentedasmean±SD.HR:heartrate;%HRmax pred:percentageofHRmaximumpredicted;SpO2:peripheraloxygensaturation.
1000 500 0 -500 -1000 0 500 1500 2000 2500 -266.5 (ISWT1 + ISWT2) /2 ISWT1 - ISWT2 235.5 1000
Figure1 Bland&Altmanplotofthedifferencebetweenthe first and second ISWT plotted against the mean of the first andsecondISWT.Theboldlinerepresentsthemeandifference betweenISWT1andISWT2andthedottedlinesthe95%limits ofagreement(n=130).
ISWTpredictiveequation
The assumptions of linearity, independence of errors, homoscedasticity, unusual pointsand normality of residu-alswereverified.Usingamultiplelinearregression,itwas foundthatsex,ageandBMIwerestatisticallysignificant pre-dictorsoftheISWT(ANOVAp<0.001)andtogetherexplained 54% of their variability. Unstandardized regression coeffi-cients(B),95%confidenceintervalsandstandarderrorsof thecoefficientsarepresentedinTable3.
Based on the multiple linear regression model,
the equation to predict ISWT was: ISWT
pre-dicted=342.06+(283.07×sex)+(83.61×age)− (22.22×BMI),withfemale=0andmale=1.
There was a significant difference between the actual ISWTandthepredictedISWTcalculatedwiththeequation establishedbyLanzaetal.(1165.1±327.2vs.1058±152.6;
p<0.001).Amoderatecorrelationwasfoundbetweenthese twovalues (r=0.69; p<0.001). The Bland & Altman plot alsoshowedpooragreementandlargelimitsofagreement betweentheactualISWTandthepredictedISWTobtained withtheequationestablishedbyLanzaetal.13 (mean
dif-ference--- 107.1m)(Fig.2).
Discussion
Thepresentstudyestablishedapredictiveequationforthe ISWT distance in healthy Portuguese children and adoles-cents. Sex, age and BMI were included in this predictive equation,explaining54% of the variance in theISWT dis-tance.
Excellent reliability was found between the two ISWT performed, which is consistent with the previous study published on the pediatric population.13 Results of our
study demonstrated that the mean ISWT distance for healthy Portuguese children and adolescents aged 5---17
Table3 SummaryofmultipleregressionanalysisforISWTdistanceasdependentvariable.
Variable B(95%CI) Std.error p-value
Constant 342.06(76.52---607.60) 134.17 0.012
Sex(female=0) 283.07(204.55---361.59) 39.68 <0.001
Age 83.61(66.37---100.86) 8.72 <0.001
BMI(kg/m2) −22.22(−35.96---8.49) 6.94 0.002
R2 54%
BMI:bodymassindex.
ISWT
pred
- ISWT
actual
ISWT
pred + ISWTactual) /2
1000 500 0 -500 -1000 0 500 1500 2000 -592.0 377.8 1000
Equation from Lanza et al.
Figure2 Bland&Altmanplotofthedifferencebetweenthe actual and the predicted (from the equation established by Lanzaetal.13)valueoftheISWTplottedagainstthemeanof theactualandthepredictedvalueoftheISWT.Theboldline representsthemeandifferenceandthedottedlinesthe95% limitsofagreement.
yearsoldwas1165.08±327.19m,presentinglarge variabil-ity(340---2250m). This variabilitycanbe explainedbythe differentdemographic andanthropometric characteristics of oursample, suchas age,sex, height,weight, physical activitylevelsandperipheralmusclestrength.29Large
vari-abilityintheISWThasalsobeenreportedinhealthychildren andadolescents(aged6---18yearsold)13andhealthyadults
(aged18---83yearsold).12Otherpossibleexplanationsofthe
variability of the performance are, the state of maturity relatedto pre/post pubertal status, the day of measure-ment (weekday or weekend) and socioeconomic status,30
however,inthepresentstudytheseaspectswerenot eval-uated.
Someofthevariablesoftheproposedequationtopredict theISWThavebeenpreviouslyusedinequationsdeveloped for healthy Brazilian children/adolescents,13 adults12 and
healthy Britishadults10 and presented similarcoefficients
of determination(48%, 50% and71%, respectively).3,9,11,12
Ourfindingsshowed that boys(1319.33±359.78) reached longer distances than girls (1032.86±225.90). In studies establishing pediatric reference equations for the 6MWT similarfindingswerereported.Reasonsforthesedifferences werethatadolescentsandboysweretaller,morephysically activeandpresentedhighermusclestrengththangirlsand children.31---33Therefore,itisnotsurprisingthatinthisstudy,
asinsimilarstudies,sexandageareincludedinpediatric predictiveequationsofcardiorespiratoryfieldtests.13,31,34,35
Anegative link wasalso observed between the ISWT and the BMI,i.e., for higher valuesof BMI,the distance cov-ered inthe ISWT wasshorter. This maybe relatedtothe effort required to perform the walking test due to par-ticipantweighing more.36 In fact, a relationship between
increasedbodyfat inadolescenceandthe lowerlevelsof physicalactivityhasbeensuggested.37
Insum,referenceequationsarevaluabletoolsfor inter-preting ISWT results obtained from healthy individuals andpatients withchronicdiseases, considering the exter-nal paced nature of the walk test and the nonexistence of interference from external factors, such as operator encouragement.11Anothermotivationforestablishing
refe-rence equations is the simplicity of predicting the ISWT, requiring only simple and quick measurements obtained in clinical practice. This is of special importance for the pediatric population with which it is often challenging to establishtherelativelylongperiodsofcollaborationneeded to carry out a cardiorespiratory assessment test. Predic-tiveequations,suchtheoneproposedinthisstudy,provide guidance for levels of disability, lead toprescription and individualizationofaerobicexercisesandlevelsofphysical activity,promotethefollow-upoftheevolutionofchildren or adolescents in fitness and rehabilitation programs and facilitate comparisonsacrosspopulations.The importance ofproducingreferenceequationsthatarespecifictoageand cultureishighlightedbytheinabilityofapredictive equa-tiondevelopedinaBrazilianpediatriccohorttoaccurately estimateISWT distance performed by Portuguese children andadolescents.Infact,whenthatequationwasappliedin oursample,thepredictedvaluewasgreatlyunderestimated whencomparedwiththeactualISWT.
Somelimitations of this study shouldbe considered. A conveniencesamplerecruitedfromasingleregionwasused, althoughcarewastakentoadjustthenumberofparticipants ineachagegroupandtheproportionofmalesandfemales. Therefore,futureresearchisneeded,e.g.,thisstudycould bereplicatedinalargersampleincludingchildrenfrom dis-tinctcountryregions.TheaverageheartrateaftertheISWT presentedasapercentageoftheheartratemaximum pre-dictedwasaround60%.Thiswaslowerthanpreviousstudies inbothpediatricandadultpopulations,whichachievedpost heartrates ofaround90%ofthepredictedvalue.12,13This
differencemayberelatedtothetimingoftheassessment. Inourstudy,theheartratewasnotregisteredimmediately after the end of the test. When the test ended, partici-pantswererecommendedtowalkfor1---2minandonlyafter thisweretheheartrateandbloodpressurereassessed.This studyusedtheconventionalformulaofBMIasanindexof obesityin anattempttosimplify theuseofthereference equation in clinical practice. Nevertheless, asin children and adolescents BMI is age- and sex-specific, commonly knownasBMI-for-age,39 thisvariablecouldbeexploredin
future studies. The obtained coefficient of determination wasmodest(54%),increasingthechanceofbiasinpredicting
thewalkingdistanceintheISWT.Theselimitationsconfine thegeneralizationofthepredictiveequationtoPortuguese children and adolescents. As an alternative to the multi-ple linear regression model used in the present study,it might be interesting tocompare it withan artificial neu-ralnetwork-basedequationmodel.Thismodelisbasedon somepropertiesofthebiologicalnervoussystemandonthe analogiesofadaptivebiologicallearning,40usinganetwork
combinationoftheinputsandthelearningeffecttofindthe bestfunctionalfitforasetofinput---outputexamples.41
Conclusions
ThisstudyestablishedapredictiveequationfortheISWT dis-tance,inwhichage,sexandBMIweremajorcontributors, accountingfor54% ofthe ISWTvariability. Thispredictive equation is a valuable tool for interpreting ISWT results obtainedfrompediatricpopulations,bothhealthyandwith chronicdiseases.
Funding
CJ has a post-doctoral grant (SFRH/BPD/115169/2016) fundedbyFundac¸ãoparaaCiênciaeaTecnologia(FCT), co-financedbytheEuropeanSocialFund(POCH)andPortuguese national funds from MCTES. The work was also partially funded by Programa Operacional de Competitividade e Internacionalizac¸ão---COMPETE,throughFundoEuropeude Desenvolvimento Regional --- FEDER (POCI-01-0145-FEDER-007628), FCT (PTDC/DTPPIC/2284/2014) and under the projectUID/BIM/04501/2013andUID/BIM/04501/2019.
Conflict
of
interest
Theauthorshavenoconflictsofinteresttodeclare.
Acknowledgments
Theauthorswouldliketoacknowledgetheparticipantsand theschoolsenrolledinthisstudy.
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