The Steep Ramp Test in Dutch WhiteChildren and Adolescents: Age- andSex-Related Normative ValuesBart C. Bongers, Sanne I. de Vries, Joyce Obeid, Stef van Buuren,Paul J.M. Helders, Tim Takken
Background. The Steep Ramp Test (SRT), a feasible, reliable, and valid exercisetest on a cycle ergometer, may be more appealing for use in children in daily clinicalpractice than the traditional cardiopulmonary exercise test because of its shortduration, its resemblance to children’s daily activity patterns, and the fact that it doesnot require respiratory gas analysis.
Objective. The aim of the present study was to provide sex- and age-relatednormative values for SRT performance in Dutch white children and adolescents whowere healthy and 8 to 19 years old.
Design. This was a cross-sectional, observational study.
Methods. A total of 252 Dutch white children and adolescents, 118 boys (meanage�13.4 years, SD�3.0) and 134 girls (mean age�13.4 years, SD�2.9), performedthe SRT (work rate increment of 10, 15, or 20 W�10 s�1, depending on body height)to voluntary exhaustion to assess peak work rate (WRpeak). Normative values arepresented as reference centiles developed by use of generalized additive models forlocation, scale, and shape.
Results. Peak work rate correlated highly with age (r�.915 and r�.811), bodymass (r�.870 and r�.850), body height (r�.922 and r�.896), body surface area(r�.906 and r�.885), and fat free mass (r�.930 and r�.902) in boys and girls,respectively. The reference curves demonstrated an almost linear increase in WRpeakwith age in boys, even when WRpeak was normalized for body mass. In contrast,absolute WRpeak in girls increased constantly until the age of approximately 13 years,when it started to level off. Peak work rate normalized for body mass in girls showedonly a slight increase with age until 14 years of age, when a slight decrease in relativeWRpeak was observed.
Limitations. The sample may not have been entirely representative of the Dutchpopulation.
Conclusions. The present study provides sex- and age-related normative valuesfor SRT performance in terms of both absolute WRpeak and relative WRpeak, therebyfacilitating the interpretation of SRT results by clinicians and researchers.
B.C. Bongers, PhD, Child Develop-ment and Exercise Center, Wil-helmina Children’s Hospital, Uni-versity Medical Center Utrecht,Utrecht, the Netherlands.
S.I. de Vries, PhD, TNO Depart-ment of Healthy Living, ExpertiseCenter Lifestyle, Leiden, theNetherlands.
J. Obeid, MSc, Child Health andExercise Medicine Program,McMaster University and McMas-ter Children’s Hospital, Hamilton,Ontario, Canada.
S. van Buuren, PhD, TNO Depart-ment of Healthy Living, ExpertiseCenter Lifestyle.
P.J.M. Helders, PT, PhD, ChildDevelopment and Exercise Cen-ter, Wilhelmina Children’s Hospi-tal, University Medical CenterUtrecht.
T. Takken, PhD, Child Develop-ment and Exercise Center, Wil-helmina Children’s Hospital, Uni-versity Medical Center Utrecht,KB.02.056.0, PO Box 85090,3508 AB Utrecht, the Nether-lands. Address all correspondenceto Dr Takken at: [email protected].
[Bongers BC, de Vries SI, Obeid J,et al. The Steep Ramp Test inDutch white children and adoles-cents: age- and sex-related nor-mative values. Phys Ther.2013;93:1530–1539.]
Physical fitness or aerobic capac-ity is an important determinantof overall health. Aerobic capac-
ity is typically assessed by measuringpeak oxygen uptake (VO2peak) asan approximation of maximal oxygenuptake1 during maximal cardiopul-monary exercise testing (CPET), thegold standard for assessing VO2peak.However, standardized exercise test-ing remains underused in manyhealth care centers.2–4 Moreover,CPET is not feasible in clinical pop-ulations in whom maximal testingis contraindicated or when perfor-mance may be impaired by pain,shortness of breath, or fatigue ratherthan exertion.5 Thus, a simple, short,inexpensive, reliable, valid, and lessphysically demanding alternativeexercise test may increase the useof exercise testing in daily clinicalpractice.
The Steep Ramp Test (SRT) is a shortmaximal exercise test that does notrequire respiratory gas analysis mea-surements. The main outcome of theSRT is the achieved peak work rate(WRpeak), which partially reflectsanaerobic power and leg musclestrength.6 The fact that performanceon the SRT depends more on anaer-obic capacity than performance onCPET implies that the SRT reflectschildren’s daily activity patterns(short bursts of intense exercise)more appropriately. Performing theSRT may be better tolerated by spe-cial populations with chronic dis-ease than performing CPET, as theSRT seemingly places a smaller bur-den on the cardiopulmonary systembecause of its short duration, as evi-denced by significantly lower valuesfor peak heart rate (HRpeak) andpeak minute ventilation (VEpeak).7
An additional advantage of the SRTis the demonstrated strong associa-tion between the WRpeak attainedin the SRT and the VO2peak obtainedfrom traditional CPET, as reportedin children who were healthy(r�.958)7 and adults who survived
cancer (r�.850).8 Therefore, theSRT may be useful as a simple screen-ing tool to provide a clinician withan indication about a child’s aerobiccapacity. A child with significantlyreduced SRT performance (WRpeak)can be referred for extensive maxi-mal CPET to evaluate precisely theintegrated physiological response toexercise.
Although the SRT appears to be apromising alternative to CPET forevaluating aerobic capacity in dailyclinical practice, the lack of norma-tive values for the test limits a clini-cian’s ability to interpret SRT perfor-mance. Therefore, the objective ofthis study was to provide sex- andage-related normative values for SRTperformance in children and adoles-cents who were healthy and 8 to 19years old.
MethodParticipantsIn this cross-sectional, observationalstudy, children and adolescents whowere healthy and 8 to 19 years oldwere recruited from primary andsecondary schools throughout theNetherlands to perform a singleSRT to volitional exhaustion. Writteninformed consent was obtained fromthe parents or guardians; potentialparticipants who were more than 12years old also were asked to providewritten consent. Children and ado-lescents who had cardiovascular,pulmonary, neurological, or muscu-loskeletal disease were excluded. Allpotential participants completed amodified Physical Activity ReadinessQuestionnaire before participationto ensure safety. Children and ado-lescents who answered “yes” to 1or more questions on the modifiedPhysical Activity Readiness Ques-tionnaire also were excluded.
AnthropometryBefore exercise testing, participantbody mass (determined to the near-
est 0.1 kg) and body height (deter-mined to the nearest 0.5 cm) weremeasured with an electronic scale(Seca 803, Seca, Hamburg, Germany)and a metric measuring tape with awall stop, respectively. Sitting heightalso was measured and was used topredict age from peak height veloc-ity as a marker of biological matu-rity.9 Body mass index (kg�m�2) wascalculated as the body mass dividedby the body height squared. Standarddeviations were calculated for bodyheight for age, body mass for age,and body mass index for age byuse of Dutch normative values.10
The equation of Haycock et al11 wasused to estimate body surface area(meters squared). Subcutaneous fatdistribution was measured with aHarpenden skinfold caliper (BatyInternational, West Sussex, UnitedKingdom) at triceps, biceps, sub-scapular, and suprailiacal sites on theright side of the body.12 The sum ofthe 4 skinfolds (millimeters) wasused to estimate the body densitywith standard equations.12 The per-centage of body fat and the fat-freemass (kilograms) were estimatedwith a modification of the Siri equa-tion proposed by Weststrate andDeurenberg.13
Available WithThis Article atptjournal.apta.org
• eTable 1: Habitual PhysicalActivity of Participants
• eTable 2: Age- and Sex-RelatedNormative Values for Peak WorkRate and WRpeak Normalized forBody Mass in the Steep RampTest and TraditionalCardiopulmonary Exercise Testing
• eFigure: Relationship BetweenBody Mass Index and Age forBoys and Girls
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November 2013 Volume 93 Number 11 Physical Therapy f 1531
AccelerometryFor the assessment of habitual phys-ical activity, all participants wereasked to wear an accelerometer ontheir right hip for 7 consecutive daysduring all waking hours, exceptwhen engaging in water activities.For practical purposes, 2 differenttypes of accelerometers were used:the ActiGraph GT3X (Actigraph LLC,Pensacola, Florida) and the Actical(Minimitter/Respironics, Bend, Ore-gon). Activity was recorded in15-second epochs on both devices.Participants who adhered to theinstructions were defined as thosewho wore the accelerometer for atleast 600 min�d�1 for a minimumof 4 days (including 1 weekend day).Average wear time (min�d�1), timespent sedentary (min�d�1), timespent in light physical activity(min�d�1), time spent in moderatephysical activity (min�d�1), timespent in vigorous physical activity(min�d�1), time spent in moderate tovigorous physical activity (min�d�1),and time spent in total physicalactivity (min�d�1) were determinedon the basis of the count cutpointsdefined by Evenson et al.14
SRTFor reduced variability in testing, allSRTs were supervised by 1 experi-enced exercise physiologist (B.C.B.)and were performed on an electron-ically braked cycle ergometer (LodeCorival, Lode BV, Groningen, theNetherlands) with a standardizedprocedure validated in a previousstudy.7 With this procedure, the SRTwas found to be a reliable exercisetest (intraclass correlation coeffi-cient�.986, P�.001).7 The averagedifference between 2 SRTs was�6.4 W (mean between-test time�8 days, SD�5), with limits of agree-ment of �24.5 and �37.5 W.7
Hence, the minimal detectablechange was 30.9 W (11%).
Seat height was adjusted to a com-fortable leg length for each partici-
pant. A modified SRT protocol wasused.7 In brief, after a 3-minutewarm-up at 25 W, the test beganwith the application of resistance of10, 15, or 20 W�10 s�1 in a ramplikemanner (2, 3, or 4 W�2 s�1), on thebasis of the participant’s body height(�120 cm, 120–150 cm, or �150cm, respectively). The participantwas instructed to maintain a pedal-ing rate of between 60 and 80 rpm.The test was terminated when theparticipant could no longer maintainthe minimum required pedalingrate of 60 rpm, despite strong ver-bal encouragement (standardized)(Appendix). Heart rate (bpm) wasmonitored throughout the test (PolarT31 transmitter, Polar, Kempele, Fin-land). The WRpeak was defined asthe work rate (watts) at peak exer-cise, the point at which the partici-pant’s pedaling frequency definitelydropped below 60 rpm. The HRpeakwas defined as the highest valueachieved during the last 30 secondsbefore test termination. Before anddirectly after the SRT, participantscompleted a 10-point visual analogscale indicating their level of fatigue,allowing us to gain a better under-standing of the exhaustiveness of theSRT (by subtracting the visual analogscale score before the test from thatafter the test).
Data AnalysisData analysis was performed withthe Statistical Package for the SocialSciences (SPSS version 15.0, SPSSInc, Chicago, Illinois). All data wereexpressed as mean, standard devia-tion, and range. Tests for normalitywere performed on the SRT datawith Kolmogorov-Smirnov tests. Dif-ferences between boys and girlswere examined with independent-sample t tests. A 2-way independentanalysis of variance was used toidentify significant differences inthe WRpeak achieved during theSRT by boys and girls within the dif-ferent age groups. Independent-sample t tests with the Holm-
Bonferroni method to counteractthe problem of multiple compari-sons were then performed to locatethe exact significant differencesbetween boys and girls. Pearson cor-relation coefficients were calculatedto examine associations between theWRpeak attained in the SRT and var-ious anthropometric variables.
Reference curves were computed asfollows: 8 models were fitted, includ-ing all combinations of the 2 mainoutcomes of the SRT (WRpeak andWRpeak normalized for body mass),2 predictors (age and body mass),and sex. The outcome distributionswere fitted as smooth functionsof the predictors through the least-mean-square model with cubicsplines.15 The parameters were esti-mated by use of generalized additivemodels for location, scale, and shape(GAMLSS 4.1-2),16 and the degree ofsmoothing needed was chosen bymeans of the worm plot with 9panels.17 Computations were per-formed with the open source statis-tical package R (version 2.14.2, RFoundation for Statistical Comput-ing, Vienna, Austria). A P value ofless than .05 was considered statisti-cally significant.
Role of the Funding SourceThis study was funded by an uncon-ditional research grant from Scien-tific Committee Physiotherapy ofthe Royal Dutch Society forPhysiotherapy.
ResultsOf the initial 266 young people whowere willing to participate and gavewritten informed consent, 252 weretested (118 boys and 134 girls; meanage�13.4 years, SD�3.0 [boys] or2.9 [girls] years, range�8–19). Fivechildren were excluded because ofmusculoskeletal disease, 2 had neu-rological disease, 2 had cardiovascu-lar disease, 3 children felt pain intheir chest when performing physi-cal activity in the month before exer-
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cise testing, and 2 children were nottested because of scheduling issues.
The characteristics of the partici-pants are shown in Table 1. Com-pared with girls, boys had signifi-cantly less biological maturity, lowerpercentage of body fat, and higherfat-free mass. eTable 1 (availableat ptjournal.apta.org) shows thehabitual physical activity of theparticipants. Boys had higher levelsof total physical activity, perhapsbecause boys spent more time inmoderate to vigorous physical activ-ity and vigorous physical activitythan girls.
All participants performed a maxi-mal SRT without any complicationsor adverse events. They all showedsubjective signs of maximal effort,including unsteady biking, sweating,facial flushing, and a clear unwilling-ness to continue despite strong ver-bal encouragement. The majority ofthe participants (n�191) also showedobjective signs of maximal effort, asindicated by an HRpeak of greaterthan 180 bpm.
All exercise variables were normallydistributed and are shown in Table 2.The mean duration of the SRT(excluding warm-up) was 129 sec-onds (SD�38). Compared with girls,
boys cycled significantly longer,resulting in significantly higher val-ues for WRpeak. Peak work ratenormalized for body mass also wassignificantly higher in boys. Boysexperienced the SRT as being moreexhaustive, as indicated by thegreater difference between the levelof fatigue before the test and thelevel of fatigue after the test (changein visual analog scale score) in boys;however, HRpeak was not signifi-cantly different between boys andgirls. An analysis of covariance withsex and age as covariates demon-strated that there was no signifi-cant difference in SRT performancebetween children living in a rural
Table 1.Characteristics of Participantsa
Characteristic
Boys (n�118) Girls (n�134)
P 95% CIX SD Range X SD Range
Age (y) 13.4 3.0 8.1–19.0 13.4 2.9 8.2–19.0 .879 �0.67 to 0.79
Body mass (kg) 51.6 15.6 23.6–104.2 50.6 13.8 21.5–97.8 .563 �2.57 to 4.71
Body height (m) 1.61 0.15 1.26–1.91 1.58 0.12 1.23–1.87 .099 �0.01 to 0.06
Age predicted from peakheight velocity (y)b
�0.36 2.41 �4.00–4.00 1.11 2.14 �3.40–4.00 �.001 �2.04 to �0.91
a CI�confidence interval, BMI�body mass index, BSA�body surface area, FFM�fat-free mass.b Calculated with the equation of Mirwald et al.9cCalculated with the equation of Haycock et al.11
dCalculated with the equations of Deurenberg et al12 and Weststrate and Deurenberg.13
Table 2.Steep Ramp Test Resultsa
Parameter
Boys (n�118) Girls (n�134)
P 95% CIX SD Range X SD Range
Duration (s) 140 44 61–239 120 28 63–193 �.001b 11.0 to 29.5
a CI�confidence interval, WRpeak�peak work rate (maximal short-time exercise capacity), HRpeak�peak heart rate, �VAS�difference in participants’ level offatigue as scored on a visual analog scale (score after test minus score before test).b Significant at P�.001.c Significant at P�.01.d HRpeak could not be determined in 1 boy and 2 girls, so for this parameter, n�117 for boys and n�132 for girls.
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November 2013 Volume 93 Number 11 Physical Therapy f 1533
area (n�103) and children living inan urban area (n�149), as indicatedby both WRpeak (276 W and 266 W,respectively; P�.136, 95% confi-dence interval��3.02 to 22.15) andWRpeak normalized for body mass(5.4 W�kg�1 and 5.3 W�kg�1, respec-tively; P�.304, 95% confidenceinterval��0.10 to 0.32).
High correlations were observedbetween WRpeak and variousanthropometric variables, as shownin Table 3 for boys and girls sepa-rately. As expected, WRpeak waspositively associated with age, bodymass, body height, biological matu-rity, body surface area, and fat-freemass (r�.811–.930, with P�.001 forall coefficients). Moderate positivecorrelations were found betweenWRpeak and body mass index; con-versely, no correlation was foundbetween WRpeak and percentage ofbody fat.
Figure 1 (top graphs) shows the age-related reference centile charts forabsolute WRpeak in the SRT for boysand girls. The values demonstrate analmost linear increase in WRpeakwith chronological age; however,commencing at an age of 13 or 14years, WRpeak began to level off in
girls but continued to increase lin-early in boys. When normalized forbody mass, WRpeak showed analmost linear increase with chrono-logical age up to 19 years of age inboys, as indicated by the age-relatedcentile charts in Figure 1 (bottomgraphs). In girls, WRpeak normal-ized for body mass showed only aslight increase with chronologicalage until 14 years of age, when aslight decrease was observed.
When WRpeak and WRpeak normal-ized for body mass were modeledagainst body mass (Fig. 2), the sametrends in the study outcomes werefound. Of special interest were thedistributions of WRpeak normalizedfor body mass as a function of bodymass (Fig. 2, bottom graphs). Forboys, peak performance occurred ata body mass of approximately 60 kg,whereas in girls, WRpeak normalizedfor body mass rapidly declinedbeyond a body mass of approxi-mately 55 kg.
eTable 2 (available at ptjournal.apta.org) shows the age- and sex-relatednormative values for WRpeak andWRpeak normalized for body mass,including standard deviations, forthe SRT as well as for traditional
CPET according to the Godfrey pro-tocol18 (previously described forDutch children19).
Boys attained significantly higherabsolute WRpeak values than girlsby the age of 15 years and beyond(Fig. 3, top graph). For WRpeaknormalized for body mass (Fig. 3,bottom graph), there seemed to bea trend toward higher values beingachieved by boys than by girlsbetween 11 and 15 years of age.Beyond this age, the differencebetween boys and girls became sig-nificant. The eFigure (available atptjournal.apta.org) shows the rela-tionship between body mass indexand age for the study sample.
DiscussionThe objective of the present studywas to provide sex- and age-relatednormative values for the WRpeakattained during the SRT by childrenand adolescents who were healthyand 8 to 19 years old. The SRT wasoriginally developed and describedas an alternative measure for deter-mining and readjusting trainingworkload for adult patients withchronic heart failure.6,20 Since then,it has been applied in the rehabilita-tion setting, specifically for prescrib-ing training load and monitoringtraining progress, for various groupsof adult patients, including patientswith cancer,8 chronic obstructivepulmonary disease,21 type 2 diabe-tes,22 and chronic heart failure.23
The SRT has several advantages overtraditional CPET in daily clinicalpractice. First, the test duration isrelatively short, 2 to 3 minutes,excluding warm-up; the duration ofCPET is 8 to 12 minutes (excludingwarm-up). Second, the SRT does notrequire expensive respiratory gasanalysis measurements. In most clin-ical practice settings, health careprofessionals do not have access toa metabolic cart. In addition, the useof a face mask or mouthpiece might
Table 3.Pearson Correlation Coefficients for Peak Work Rate and Anthropometric Variablesa
Variable
Boys (n�118) Girls (n�134)
r P r P
Age (y) .915 �.001 .811 �.001
Body mass (kg) .870 �.001 .850 �.001
Body height (m) .922 �.001 .896 �.001
Age predicted from peakheight velocity (y)b
.949 �.001 .879 �.001
BMI (kg�m�2) .564 �.001 .601 �.001
BSA (m2)c .906 �.001 .885 �.001
Body fat (%)d �.019 NS .211 .014
FFM (kg) .930 �.001 .902 �.001
a BMI�body mass index, BSA�body surface area, NS�not significant, FFM�fat-free mass.b Calculated with the equation of Mirwald et al.9c Calculated with the equation of Haycock et al.11
d Calculated with the equations of Deurenberg et al12 and Weststrate and Deurenberg.13
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frighten young children.24 Third, theSRT is known to be a reliable maxi-mal exercise test and seems to placea much smaller burden on the car-diopulmonary system than tradi-tional CPET, despite the fact that theWRpeak attained in the SRT is about1.5 times higher than that attainedin CPET (eTab. 2).7 This result is dueto the faster work rate incrementsin the SRT than in CPET (the work
rate increases 6 times faster in theSRT), resulting in higher WRpeakvalues and lower HRpeak andVEpeak values being attained in theSRT. The significantly lower HRpeakand VEpeak values attained in theSRT than in CPET suggest that localmuscle fatigue limits performance inthe SRT. Nevertheless, Bongers et al7
reported high correlation coeffi-cients between the WRpeak attained
during the SRT and the VO2peakachieved during traditional CPET(r�.958, P�.001). They developed aprediction model that estimates theVO2peak from the WRpeak attainedin the SRT. Perhaps most impor-tantly, Bongers et al7 also showedthat the SRT is safe and easily per-formed by children. Through theconstruction of reference curveswith age-related reference centiles
Figure 1.Age-related centile charts for the absolute peak work rate (WRpeak) (top graphs) and peak work rate normalized for body mass(bottom graphs) in the Steep Ramp Test for boys and girls separately. Dotted lines represent the 50th centile (P50); dashed linescorrespond to the 10th, 25th, 75th, and 90th centiles (P10, P25, P75, and P90, respectively); and solid lines indicate the 3rd and97th centiles (P3 and P97, respectively).
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November 2013 Volume 93 Number 11 Physical Therapy f 1535
for the absolute WRpeak and the rel-ative WRpeak, the SRT results nowhave become easy for clinicians tointerpret.
For daily clinical practice, the SRTmay be valuable as a simple screen-ing tool to indicate a child’s aerobiccapacity. A WRpeak in the SRT thatis significantly below average indi-cates that the child may have areduced aerobic capacity compared
with peers who are healthy. Becausethe SRT should not be used as a sub-stitute for traditional CPET, a childwith reduced SRT performanceshould be referred for traditionalCPET to assess the integrated physi-ological response of the cardio-vascular, pulmonary, and musculo-skeletal systems to progressiveexercise up to voluntary exhaus-tion. As a cutoff point for indicatingreduced SRT performance, an abso-
lute WRpeak or a relative WRpeak(or both) that falls below the thirdpercentile of the presented refer-ence curves can be used.
The SRT examines aerobic power aswell as anaerobic power. It is evidentthat with growth there are concom-itant increases in aerobic power andanaerobic power. Our results indi-cated that boys attained significantlyhigher absolute WRpeak values than
Figure 2.Body mass–related centile charts for the absolute peak work rate (WRpeak) (top graphs) and peak work rate normalized for body mass(bottom graphs) in the Steep Ramp Test for boys and girls separately. Dotted lines represent the 50th centile (P50); dashed linescorrespond to the 10th, 25th, 75th, and 90th centiles (P10, P25, P75, and P90, respectively); and solid lines indicate the 3rd and97th centiles (P3 and P97, respectively).
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girls as of 15 years of age and beyond(Fig. 3, top graph). This finding isin line with those of several studiesinvestigating aerobic power andanaerobic power in boys and girls.Bar-Or and Rowland25 presentedmaximal aerobic power (VO2peak)data in relation to the chronologicalage of 3,910 boys and girls between6 and 18 years old (originating frommultiple cross-sectional studies).They reported that VO2peak valuesincreased until the age of 17 or 18years in boys, whereas VO2peak val-ues hardly increased beyond 14years of age in girls. These data wereconfirmed by VO2peak normativevalues based on cross-sectional datafor a representative group of Dutchchildren who were 6 to 18 yearsold.26 Regarding the developmentof anaerobic power with age, girlsgenerally had lower values thanboys, and the difference becamemore apparent at 14 years of age andbeyond.25 Van Praagh27 used datafrom a study28 investigating the abso-lute cycling peak anaerobic power inrelation to age in boys and girls andfound that girls began diverging fromboys at the age of 13 or 14 years,with significantly lower values beingreported for girls as of 14 or 15 yearsof age.
The sex-associated variation in aero-bic power and anaerobic powerand therefore in SRT performanceis most likely caused by a greaterincrease in muscle mass with age inboys as well as by a greater increasein body fat with age in girls. Theseincreases are largely related tochanges in endocrine functionthroughout puberty,29 with testos-terone playing an important role inthe gain of muscle strength in boys.30
Fiber type distribution and neuraladaptation may be factors in age-associated differences in musclestrength.31 Sex-associated differ-ences, especially postpubertal, werealso reported for grip strength (a pre-dictor of overall muscle strength),
with higher values being attained inboys.32 In the present study, the pre-pubertal sex-associated differences(nonsignificant) in relative WRpeakvalues were likely associated withthe higher proportion of body fat ingirls.
LimitationsAlmost all of the participants in thepresent study were white. Whetherthe normative values reported hereare valid for other ethnic groupsremains to be determined. More-over, standard deviations for bodymass for age were significantly differ-ent from Dutch population norms ingirls (�0.19 SD [P�.031]), whereasstandard deviations for body massindex for age were significantly dif-
ferent from general populationnorms in boys and girls (�0.29 SD[P�.002] and �0.24 SD [P�.006],respectively).11 Despite the fact thatthese differences were small, thesample might not be entirely repre-sentative of the Dutch population.Standard deviations for body heightfor age did not differ significantlyfrom Dutch normative values in boysand girls.11
ConclusionThe present study provides sex- andage-related normative values (pre-sented as reference centiles) for SRTperformance in terms of both abso-lute WRpeak and relative WRpeak.The reference curves demonstratedan almost linear increase in WRpeak
Figure 3.Age-related sex differences for the absolute peak work rate (WRpeak) (top graph) andpeak work rate normalized for body mass (bottom graph) in the Steep Ramp Test. Dataare expressed as means and standard deviations.
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November 2013 Volume 93 Number 11 Physical Therapy f 1537
with age in boys up to 19 years old,even when WRpeak was normalizedfor body mass. In contrast, WRpeakin girls increased constantly until theage of approximately 13 years, whenWRpeak started to level off. Peakwork rate normalized for body massshowed only a slight increase withage in girls, and a slight decrease inrelative WRpeak commenced at 14years of age. Given the expense andtechnical nature of measuring maxi-mal oxygen uptake, the availabilityof reference curves for the SRT maysimplify the interpretation of thisclinically useful alternative to tradi-tional CPET.
Dr de Vries, Dr Helders, and Dr Takkenprovided concept/idea/research design. DrBongers, Dr van Buuren, and Dr Heldersprovided writing. Dr Bongers and Dr Takkenprovided data collection. Dr Bongers, MsObeid, Dr van Buuren, and Dr Takken pro-vided data analysis. Dr Bongers, Dr Helders,and Dr Takken provided project manage-ment. Dr Helders and Dr Takken providedfund procurement. Dr de Vries and DrTakken provided facilities/equipment. Drde Vries and Ms Obeid provided consulta-tion (including review of manuscript beforesubmission).
The authors are grateful to Lode BV, Gro-ningen, the Netherlands, and ProCare BV,Groningen, the Netherlands, for technicalsupport during this study. They also thankIVECO Schouten, Utrecht, the Netherlands,for logistical support and Anouk Schoutenand Mark Mulder for their assistance duringdata collection. The authors thank the par-ticipating schools: Basisschool Lucas Gale-cop, Nieuwegein, the Netherlands; CalsCollege, Nieuwegein, the Netherlands;Graaf Huyn College, Geleen, the Nether-lands; Wellantcollege, Gorinchem, the Neth-erlands; and Zuyd University of AppliedSciences (School of Biometrics and Schoolof Physiotherapy), Heerlen, the Netherlands.Finally, the authors are especially grateful toall of the participants.
This study was approved by the Medical Eth-ics Committee of the University MedicalCenter Utrecht.
This study was funded by an unconditionalresearch grant from Scientific Committee
Physiotherapy of the Royal Dutch Society forPhysiotherapy.
DOI: 10.2522/ptj.20120508
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Appendix.Encouragement
Since the duration of the load phase of the Steep Ramp Test (SRT) differed among the participants, it was difficultto provide standardized encouragement throughout the test for each participant. During the first part of the SRTperformed in the present study, encouragements such as “You are doing great, come on” and “Keep on going, greatwork” were used. When it became clear that a participant was struggling during the test, the exercise physiologistsaid, “OK, keep pushing hard on the pedals; the work rate increases fast, and you should try to maintain a pedalingfrequency of about 80 rpm.” When the pedaling frequency at peak exercise started to drop toward 60 rpm (end oftest criterion), the exercise physiologist said, “Come on, this is the most important part of the test; try to performone last sprint, give everything you have got.”
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