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ERROR: type should be string, got "https://doi.org/10.1007/s00431-022-04434-7\nEuropean Journal of Pediatrics (2022) 181:2389–2397 https://doi.org/10.1007/s00431-022-04434-7\nEuropean Journal of Pediatrics (2022) 181:2389–2397 ORIGINAL ARTICLE ORIGINAL ARTICLE Comparison of two methods of cardiopulmonary exercise testing \nfor assessing physical fitness in children and adolescents with extreme \nobesity Linda Kalski1,2   · Martin Wannack3 · Susanna Wiegand3 · Bernd Wolfarth1,2 Received: 6 October 2021 / Revised: 28 February 2022 / Accepted: 3 March 2022 \n© The Author(s) 2022\n/ Published online: 12 March 2022 Abstract *\t Linda Kalski \n\t\nlinda.kalski@charite.de\n1\t\nInstitute of Sport Science, Humboldt-Universität zu Berlin, \nBerlin, Germany\n2\t\nDepartment of Sports Medicine, Charité – \nUniversitätsmedizin Berlin, Berlin, Germany\n3\t\nCenter for Social‑Pediatric Care/Pediatric Endocrinology \nand Diabetology, Charité – Universitätsmedizin Berlin, \nBerlin, Germany\nKeywords  Obesity in children and adolescents · \nCardiopulmonary exercise testing · Bicycle · Treadmill\nAbbreviations\nANOVA \t\n\u0007Analysis of variance\nBC\t\n\u0007Bicycle ergometer\nBMI\t\n\u0007Body mass index\nCPET\t\n\u0007Cardiopulmonary exercise testing\nECG\t\n\u0007Electrocardiogram\nHR\t\n\u0007Heart rate\nLA\t\n\u0007Lactate accumulation\nRPE\t\n\u0007Rating of perceived exertion\nSDS\t\n\u0007Standard deviation score Abstract It is well-known that children and adolescents with obesity have increased over recent decades which in turn carries greater \nrisk of co-morbidities and poses a preventive as well as a therapeutic challenge. Currently, there are limited recommendations \navailable on proven methods for recording physical fitness in children and adolescents presenting with extreme obesity. In \nthis study, twenty participants, aged 12–17 years, with a body mass index (BMI) above the 99.5th percentile, were compara-\ntively assessed, using a correlation between their physical fitness on a bicycle (BC) and treadmill (TM) cardiopulmonary \nexercise testing (CPET) with a lactate diagnostic. The results of the BC and the TM were as follows: maximum heart rate \n­(HRmax) 186.4 ± 8.6 beats per minute (bpm) vs. 190.8 ± 8.8 bpm, peak oxygen consumption ­(VO2peak/kg) 23.5 ± 2.9 ml/min/\nkg vs. 25.4 ± 3.1 ml/min/kg, and maximum lactate ­(Lamax) 6.4 ± 1.6 mmol/l vs. 5.6 ± 1.4 mmol/l. The values of ­HRmax and \n­VO2peak/kg were significantly higher for adolescents tested on the TM. However, no significant difference was observed in \neither ­Lamax values or between the genders. Conclusions: The higher values of ­HRmax and ­VO2peak/kg could be attributed to the activation of a higher percentage of \nmuscle mass on the TM. Lower ­Lamax values on the TM suggest maximum physical exertion was not achieved. This could \nbe due to the extreme body weight carried by the participants. Both the BC and the TM CPET could be used for assessing \nphysical fitness in children and adolescents with extreme obesity but should not be used interchangeably. 1i\nWhat is Known:\n• Currently, there are only limited recommendations available on proven methods for recording physical fitness in children and adolescents \nwith extreme obesity available. What is New:\n• Cardiopulmonary exercise testing with maximum physical exertion has been shown to be feasible in children and adolescents with extreme \nobesity. The results obtained from this study demonstrated that both a bicycle and a treadmill can be effectively used for assessing the \nphysical fitness levels in children and adolescents with extreme obesity. Communicated by Gregorio Paolo Milani\nLinda Kalski and Martin Wannack contributed equally to this \nwork. What is Known: What is Known:\n• Currently, there are only limited recommendations available on proven methods for recording physical fitness in children and adolescents \nwith extreme obesity available. What is New: What is New:\n• Cardiopulmonary exercise testing with maximum physical exertion has been shown to be feasible in children and adolescents with extreme \nobesity. The results obtained from this study demonstrated that both a bicycle and a treadmill can be effectively used for assessing the \nphysical fitness levels in children and adolescents with extreme obesity. Vol.:(0123456789)\n1 3\nCommunicated by Gregorio Paolo Milani\nLinda Kalski and Martin Wannack contributed equally to this \nwork. *\t Linda Kalski \n\t\nlinda.kalski@charite.de\n1\t\nInstitute of Sport Science, Humboldt-Universität zu Berlin, \nBerlin, Germany\n2\t\nDepartment of Sports Medicine, Charité – \nUniversitätsmedizin Berlin, Berlin, Germany\n3\t\nCenter for Social‑Pediatric Care/Pediatric Endocrinology \nand Diabetology, Charité – Universitätsmedizin Berlin, \nBerlin, Germany\nKeywords  Obesity in children and adolescents · \nCardiopulmonary exercise testing · Bicycle · Treadmill\nAbbreviations\nANOVA \t\n\u0007Analysis of variance\nBC\t\n\u0007Bicycle ergometer\nBMI\t\n\u0007Body mass index\nCPET\t\n\u0007Cardiopulmonary exercise testing\nECG\t\n\u0007Electrocardiogram\nHR\t\n\u0007Heart rate\nLA\t\n\u0007Lactate accumulation\nRPE\t\n\u0007Rating of perceived exertion\nSDS\t\n\u0007Standard deviation score 3456789)\n3 2390 European Journal of Pediatrics (2022) 181:2389–2397 TM \t\n\u0007Treadmill ergometer\nVO2peak\t\n\u0007Peak oxygen consumption\nWHR\t\n\u0007Waist-to-hip ratio in terms of their feasibility and efficiency for maximum \nphysical exertion in children and adolescents with extreme \nobesity. Additionally, possible gender-specific differences \nin physical fitness were also considered. Analysis of each \nindividual’s physical fitness could, potentially, in addition \nsubstantiate personalized therapy recommendations already \nin place. Methods Written informed consent was obtained from each partici-\npant prior to testing. All examinations were carried out at \nthe outpatient clinic of the Department of Sports Medicine at \nCharité – Universitätsmedizin Berlin/Humboldt, University \nof Berlin. Participants were recruited from the Center for \nSocial-Paediatric Care of the Charité Berlin. Physical fitness encompasses both physical and psychologi-\ncal components, although sports science only takes the physi-\ncal components into consideration. According to Weineck [5], \nphysical fitness defines the degree of expression of a certain \nsports motor performance. Physical fitness can be determined \nand assessed during maximal exercise testing. Using standard-\nized examination conditions, performance diagnostics can be \nconducted on an ergometer. Evaluation of the results enables \nathletes, as well as recreational athletes and study participants, \nto receive specific training recommendations, based on findings. Additionally, results can provide supplementary therapy plan-\nning for people who are suffering from different diseases [6]. Introduction Obesity in childhood and adolescence is a growing and \nworldwide issue [1]. The KiGGS study, a representative \npopulation-based survey [2], showed that, in Germany, \n15.4% of the adolescents are overweight and 5.9% are \nobese [3]. Extreme obesity is defined by a body mass index \n(BMI) above the 99.5th percentile. This corresponds to a \nstandard deviation score (SDS) of more than + 2.5. Extreme \nobesity in childhood and adolescence is associated with an \nincreased metabolic and cardiovascular morbidity (e.g., \ntype 2 diabetes or coronary heart disease) in adulthood [4].i Participants All participants were free of any medical condition that \ncould have affected their performance of medical measure-\nments. Exclusion criteria were individuals under 10 or over \n17 years of age and body weight < 97. Percentile or BMI \nis < 25. The participants (n = 20; f: n = 11; m: n = 9) were \n12 to 17 years of age (15.2 ± 1.6) at the time of examina-\ntion. Table 1 shows anthropometric data of the study popula-\ntion with mean values and standard deviation for age, BMI, \nBMI-SDS, body fat percentage, and achieved power of each \nCPET. Physical activity plays an important role in prevention \nand treatment of overweight and obesity in childhood and \nadolescence [7]. Indeed, several recent publications have \nput forward different types of physical activities that have \nbeen shown to be effective in fighting obesity [8–10]. Dias \net al. [10] have demonstrated how high-intensity interval \ntraining can be effective for people with obesity, especially \nby decreasing BMI-SDS and increasing cardiorespiratory \nfitness. For correct execution and highest levels of effective-\nness, high-intensity interval training needs to be performed \nat a high-level heart rate. However, there is currently very \nlittle data on adolescents with extreme obesity exercising \nat such high-level heart rates. Hansen et al. [11] found in \ntheir systematic review and meta-analysis that there are dif-\nferences between obese and lean adolescents in VO2peak \nmeasurements. Klijn et al. [12] found relevant and signifi-\ncant improvements on aerobic performance in adolescents \nwith extreme obesity following an aerobic training program. When treating children and adolescents with extreme obe-\nsity, it is essential to consider individual performance limits \nand to make recommendations based on the data. Only subjects who participated in both examinations (BC \nand TM) were included in this study. There is, therefore, no \nmissing data in this record. Study design Participants were tested in an incremental bicycle ergometry \nand running test in a laboratory setting (see protocols below) \non two different days within a time frame of 2 weeks. In the \nfirst week, the bicycle exercise test was performed with the \ntreadmill exercise test being carried out 1 week later. The \ntests were not carried out under fasting conditions, as this is \nnot recommended for maximal exercise testing. Data collec-\ntion started in July 2018 and finished in January 2019. Due \nto the pilot trial, a sample size calculation was not necessary. Anthropometric data The following anthropometric data were measured on two \ndifferent days: body height, body weight, waist-to-hip ratio \n(WHR), BMI, caliperometry, and body composition with The aim of the present study was therefore to compare \ntwo methods of cardiopulmonary exercise testing (CPET) 3 3 European Journal of Pediatrics (2022) 181:2389–2397 2391 bioelectrical impedance analysis. The average of each data \nwas subsequently calculated. p\nData of participants described as mean values and standard deviation in brackets\n n number of participants, BMI body mass index, BMI-SDS standard deviation score for body mass index, BFP body fat percentage, BFM body fat mass, BC bicycle, TM treadmill, FFM fat-free \nmass\nSex\nn\nAge [years]\nHeight [cm]\nWeight [kg]\nBMI [kg/m2]\nBMI-SDS\nBFP [%]\nBFM [kg]\nFFM [kg]\nPower, relatively \nBC [W/kg]\nPower, \nabsolutely \nTM [%]\nMale\n9\n14.3 (± 1.5)\n174.5 (± 10.0)\n112.1 (± 26.1)\n36.4 (± 4.8)\n2.9 (± 0.4)\n41.4 (± 6.7)\n46.5 (± 13.7)\n65.8 (± 15.3)\n1.2 (± 0.2)\n17.6 (± 2.3)\nFemale\n11\n15.8 (± 1.4)\n168.6 (± 8.4)\n102.7 (± 20.1)\n36.1 (± 6.0)\n3.1 (± 0.7)\n45.0 (± 4.8)\n46.8 (± 12.2)\n56.3 (± 9.0)\n1.2 (± 0.3)\n16.6 (± 2.6)\nAll\n20\n15.2 (± 1.6)\n171.3 (± 9.1)\n106.9 (± 22.4)\n36.2 (± 5.5)\n3.0 (± 0.6)\n43.4 (± 6.0)\n46.7 (± 12.9)\n60.6 (± 13.1)\n1.2 (± 0.3)\n17.0 (± 2.5) With the participant in an upright position, the body \nheight and body weight of each were measured using a cali-\nbrated scale (Seca 285 DP, Seca GmbH & Co. KG, Ham-\nburg, Germany). To calculate the BMI of each subject, the \nformula BMI = kg/m2 was used. Subsequently, waist and hip \ncircumference was measured in cm with a standardized tape \nmeasure (Seca GmbH) in cm to determine the WHR. The \nWHR is the dimensionless ratio of the circumference of the \nwaist to that of the hips and is calculated as waist measure-\nment divided by hip measurement. The anthropometry of fatty and fat-free mass was based \non caliperometry of 7 and 10 skin folds. First, the thick-\nness of designated skin folds was obtained using a caliper \n(Harpenden Skinfold Caliper, UK). A total of eleven differ-\nent points of the body were included in the measurement, \nallowing the percentage body fat to be calculated using for-\nmulas from Jackson and Pollock and Johnson and Scholz \n[13–15]. Anthropometric data Additionally, a bioelectrical impedance analysis \nwas repeated at each appointment to measure body composi-\ntion before exercise testing, to allow changes to be recorded. A body analysis scale (InBody770, JP Global Markets \nGmbH, Eschborn, Germany) was used to determine muscle, \nfat, and water proportions by measuring resistance [16, 17]. Cardiopulmonary exercise testing (CPET) After a spirometry, a bodyplethysmography was conducted \nfor each participant. Both resting pulmonary function tests \nwere performed using COSMED Q-Box with COSMED \nQuark PFT (Pavona di Albano, Italy). This procedure made \nit possible to diagnose respiratory impairment prior to CPET \n[20]. Throughout testing, ECG recordings continued to moni-\ntor recovery, ensuring 5-min rest. During the test, the blood \npressure was measured every 3 min, with a standard suitable \narm cuff, and a blood sample from the earlobe was taken \nevery 3 min for lactate diagnostic purposes. Noninvasive metabolic testing equipment (K5 Wearable \nMetabolic System, COSMED, Pavona di Albano, Italy) sup-\nplied comprehensive measurements and therefore invaluable \ninformation about physical fitness and individual exercise \nlimits, from which the training status could be generated \n[23]. Exercise testing Prior to the test, participants were informed of the impor-\ntance of maximal physical effort. They were, however, \ninstructed to immediately report any occurrence of thoracic \npain, limiting dyspnea, or dizziness experience during test-\ning. Prior to the beginning of each exercise, a clinical exami-\nnation and an inconspicuous 12-lead rest electrocardiogram \n(ECG) (Custo Cardio 200 Saug-EKG, Custo med GmbH, \nOttobrunn, Germany) were mandatory. During the test, a \n12-lead ECG (Custo Cardio 300) was continuously running \nand monitoring (Software Custo diagnostics, Version 4.6.4). After completion of the BC test, the running examination \non the TM was planned after a 1-week break. This sequence \nwas chosen deliberately, as experience has shown that the \nECG quality during BC testing is improved, and any abnor-\nmalities can be detected at an earlier stage. Both examina-\ntion methods were conducted under standardized laboratory \nconditions. The ambient temperature was between 18 and \n24 °C with a humidity of 30–60%.f Prior to the test, participants were informed of the impor-\ntance of maximal physical effort. They were, however, \ninstructed to immediately report any occurrence of thoracic \npain, limiting dyspnea, or dizziness experience during test-\ning. Prior to the beginning of each exercise, a clinical exami-\nnation and an inconspicuous 12-lead rest electrocardiogram \n(ECG) (Custo Cardio 200 Saug-EKG, Custo med GmbH, \nOttobrunn, Germany) were mandatory. During the test, a \n12-lead ECG (Custo Cardio 300) was continuously running \nand monitoring (Software Custo diagnostics, Version 4.6.4). After completion of the BC test, the running examination \non the TM was planned after a 1-week break. This sequence \nwas chosen deliberately, as experience has shown that the \nECG quality during BC testing is improved, and any abnor-\nmalities can be detected at an earlier stage. Both examina-\ntion methods were conducted under standardized laboratory \nconditions. The ambient temperature was between 18 and \n24 °C with a humidity of 30–60%.f All participants were encouraged by the medical staff to \nexercise at their maximal effort level. During the test, the \nsubjective state and the rating of perceived exertion (RPE) \nwere recorded by the BORG 20 scale (Borg RPE) [18, 19]. The end of the test was generally determined by the partici-\npants’ maximum exhaustion. 1 3 3 European Journal of Pediatrics (2022) 181:2389–2397 2392 Treadmill ergometer (TM) A constant speed on the TM (h/p cosmos sports & medical \nGmbH, Nussdorf-Traunstein, Germany) was set at 4 km/h \nwith an initial elevation of 2.5%. This was increased by 2.5% \nevery 3 min until the participant was seen to be exhausted. The protocol was selected [20] and needed to be adjusted for \neach participant, because high-speed running is not recom-\nmended for people with extreme obesity. The intensity of \nthe exercise was therefore increased by raising the elevation \nrather than the speed of the TM. Self‑reported questionnaire In order to gain further insights in the subjects’ well-being \nduring both CPET, all subjects received a short question-\nnaire at the end of the second examination. Each of the \nsubjects filled out the questionnaire themselves, providing \nsubjective feelings of perceived exertion as a supplement \nto the BORG RPE scale. The combination of both tools \nwas used so that the subjects did not have any difficulty \nin assessing their subjective perception of effort during \nexercise. Six age-appropriate questions were asked on \nparameters such as effort, joy, comfort, discomfort, moti-\nvation, and ambition, and the subjects could each choose \na preferred CPET. Between the 3-min training intervals, a 30-s rest was \ngiven to measure lactate accumulation (LA) from capillary \nblood samples taken from the earlobe. Blood pressure was \nmeasured at the beginning of the test, at the point of exertion \n(until the end of the test), and after a minimum of 5 min in \na resting position. The ECG was recorded continuously as \nin the first test on BC. The participants were able to stop the \nexamination at any time. Bicycle ergometer (BC) threshold and may serve as a basis for individually assessing \nendurance capacity and training zones. In addition, a maxi-\nmum lactate concentration provided proof of maximum exer-\ntion [22]. Adjustments were made to the height of the BC saddle \n(Ergoselect 100 k. Ergoline GmbH, Bitz, Germany) and \nhandlebars prior to testing. After a rest period of 3 min, the \nparticipants started at 25 W with a 25 W increase every \n3 min. The ideal pedaling cadence was a consistent speed \nof 60–70 RPM, and no less than 60 RPM. At the point of \nexertion, the test was concluded, and participants remained \non the BC at a low frequency with light resistance so that \nthere was no abrupt load termination. Lactate accumulation (LA) The collected anthropometry data were recorded using a \nclinic software [I/med] (Version 6.34, DORNER GmbH & \nCo. KG). Resting ECG and stress ECG were recorded using \nCusto diagnostics (Custo med GmbH Version 4.6.4). The \nresults of both pulmonary function tests and CPET were \nobtained using Omnia software from COSMED 2013/06). The data of performance diagnostics and in particular the \nLA values were visualized and recorded in Ergonizer (Ver-\nsion 5.0.1 Build 134; Röcker, 2013), and all data were trans-\nferred into an Excel spreadsheet (Microsoft Office Excel, \n2019). Data were processed with the statistical program \nSPSS (IBM, SPSS Statistics, Version 25). For descriptive \nstatistics, i.e., anthropometric data, respective mean values \nand standard deviations (SD) were calculated using SPSS. In order to be able to determine the blood lactate concentra-\ntion, capillary blood was taken from the earlobe [21]. The ear-\nlobe had already been prepared with a blood flow-enhancing \nwarming ointment (Finalgon) and then disinfected. LA was \ntaken once at rest, during the test in the last 10 s of each \nstage and 3 times during the recovery phase. Immediately \nafter the recovery phase, the blood samples were placed in \na sample tray of the lactate device EKF Diagnostics Biosen \nC-line Clinic (Barleben, Germany) and analyzed within a few \nseconds by enzymatic-amperometric chip-sensor technol-\nogy. Incremental exercise tests eliciting an increase in lactate \nvalues were then used to produce lactate curves. The lactate \ncurve could be used to determine the aerobic and anaerobic 3 1 3 3 European Journal of Pediatrics (2022) 181:2389–2397 2393 A significance level of p < 0.05 was selected in the fol-\nlowing evaluation to determine statistical significance [24]. Using SPSS, an analysis of variance (ANOVA) with repeated \nmeasures is applied as part of the inferential statistics. First, \nthe residuals were tested for assumption of normality. The \nhomogeneity of variance was subsequently proved, so that \nan ANOVA could be given [25]. ANOVA was performed \non three parameters ­(HRmax, ­Lamax, and ­VO2peak/kg) and \ncalculated for the effects of ergometry (within-subject fac-\ntor, i.e., intraindividual) and sample and supplemented with \nthe variable gender as a between-subject factor, i.e., inter-\nindividual [24]. For the scatterplots, the software R (version \n4.0.4) with the R-package ggplot2 (version 3.3.3) was used. female subjects reached 2.4 ± 0.4 l/min on BC and 2.6 ± 0.5 l/\nmin on the TM. Discussion Children and adolescents with extreme obesity are able to \nachieve maximum physical exertion on CPET. We demon-\nstrated that both the BC and the TM are suitable for CPET \nfor this specific age and weight group. The advantages of \nusing a BC are a more accurate evaluation of the exercise \nECG and a more comfortable measurement of blood pres-\nsure [26]. A sitting position is considered safer and more \ncomfortable, especially for obese patients. A conscious deci-\nsion was made to use this device because a higher muscular \nand therefore cardiovascular exertion could be achieved on a \nstandard bicycle ergometer than on a recumbent ergometer. A self-reported questionnaire revealed that the BC was more \ncomfortable and probably more familiar than the TM. This \nalso led to the assumption that the examination carried out \non the TM was perceived as more strenuous for the subjects. It is important to mention that the questionnaire is not a valid \ninstrument but was used in addition to the BORG RPE scale. On the other hand, the TM examination led to significantly \nhigher levels of HR and ­VO2peak/kg. This could be consid-\nered as a better achievement of a maximum physical exertion \n[27, 28]. Another explanation could be that due to the high \nbody weight, exhaustion and an anaerobic metabolic state \nwere reached more quickly, and thus, the maximum load is \nreached sooner. This could result in a higher percentage of \nactivated muscle mass. The subjects may have been unable \nto reach maximum muscular exertion due to reaching the \ncardiopulmonary maximum on the BC [23, 29]. Power The participants achieved a mean power of 160.4 ± 6 W on \nBC. The girls reached an average of 155.6 ± 37 W and the \nboys 166.3 ± 23.6 W. As shown in Table 1, the boys reached \na relative power of 1.2 ± 0.2 W/kg on the BC and the girls \n1.2 ± 0.3 W/kg. In relation to fat-free mass, the subjects had \na relative power of 2.7 ± 0.4 W/kg FFM. The boys reached a \nrelative power of 2.5 ± 0.3 W/kg FFM, and the girls reached \na relative power of 2.8 ± 0.4 W/kg FFM. On average, the \nparticipants achieved a 17.1 ± 3.4% slope at a constant speed \nof 4 km/h on the TM. The average load for the girls occurred \nat a mean slope of 16.6 ± 2.6%, and the boys achieved a \n17.6 ± 2.3% slope. Maximum lactate ­(Lamax) The ­Lamax average was 6.4 ± 1.6 mmol/l on the BC and \n5.6 ± 1.4 mmol/l on the TM. Female participants obtained \na ­Lamax of 6.3 ± 1.7 mmol/l on the BC and 5.5 ± 1.2 mmol/l \non the TM. Male participants achieved a ­Lamax of \n6.5 ± 1.5 mmol/l on the BC and 6.0 ± 1.8 mmol/l on the TM. Maximum heart rate ­(HRmax) The achieved ­HRmax was on average 186.4 ± 8.6 bpm dur-\ning BC testing and hence slightly lower than for TM testing \nwhich was 190.8 ± 8.8 bpm. For the female participants, the \n­HRmax was 186.7 ± 8.1 bpm on BC and 190.9 ± 6.8 bpm on \nthe TM. For the male participants, the ­HRmax on the BC was \n186 ± 9.7 bpm and 190.6 ± 11.2 bpm on the TM. Lactate accumulation (LA) Male subjects achieved 2.6 ± 0.4 l/min on the \nBC and 2.9 ± 0.5 l/min on the TM. The achieved relative ­VO2peak/kg was on average \n23.5 ± 2.9 ml/min/kg on the BC CPET and 25.4 ± 3.1 ml/\nmin/kg on the TM. The female participants reached \n23.3 ± 2.7 ml/min/kg on BC and 24.9 ± 3.4 ml/min/kg on \nthe TM. Male participants obtained 23.7 ± 3.2 ml/min/kg on \nthe BC and 26.0 ± 2.8 ml/min/kg on the TM. Self‑reported questionnaire The two methods of CPET were compared on subjective \nparameters taken from the questionnaire. Fifteen subjects \nwrote that the cycling was more enjoyable than walking \n(five). In this context, seventeen subjects also felt more com-\nfortable and safe on the BC, whereas only three subjects \npreferred the TM. Thirteen subjects reported being more \nambitious and motivated when cycling than walking (seven). In terms of effort, the TM got more votes (twelve) than the \nBC (eight). Absolute and relative ­VO2peak The absolute ­VO2peak for all subjects was, on average, \n2.5 ± 0.4 l/min on the BC and 2.7 ± 0.5 l/min on the TM. The 1 3 3 European Journal of Pediatrics (2022) 181:2389–2397 2394 was the necessity for a two-staged examination over a 1- \nto 2-week period. Forty-five families were informed and \nreceived information sheets. Twenty-five of these families \ndid not take up the opportunity. Additionally, both the BC \nand the TM represented a very unusual activity situation for \nthe participants, so that the subjective rating of maximum \nexertion (Borg RPE scale) was probably reached before max-\nimum cardiopulmonary load. One implication of the study \nwas that the examinations on the TM led to a higher level \nof motivation at the second appointment, because the par-\nticipants were eager to improve their previous achievements \n[34]. Regarding the significantly higher levels of ­HRmax and \n­VO2peak/kg in TM, this CPET should be considered as the \nmore valid one for cardiopulmonary performance assess-\nment. This is in line with findings in several other studies \n[27, 28, 35]. In this study, participants showed lower levels \nof ­Lamax on the TM. These values (p = 0.076), however, did \nnot reach a significance level of p < 0.05. A lower ­Lamax in \nthe TM compared to the BC could be due to a higher demand \nfor lactate as a source of energy by both cardiac muscle fib-\ners and the active muscles that have no heavy involvement \nin propulsion, f.e. arms and shoulder muscles [36–38]. Fur-\nther studies comparing both methods need to be performed \nto analyze whether this is due to a lower level of fitness in \nchildren and adolescents with extreme obesity or whether \nother TM protocols need to be applied. Criteria for maximum physical load (and their most com-\nmon definitions) are as follows: (I) plateau of ­VO2 (with an \nincrease of less than 150 ml/min), (II) ­HRmax (+ / − 10 bpm \nof age-dependent ­HRmax), (III) respiratory quotient RQ \n­(VCO2/VO2 > 1.10), (IV) ­Lamax (> 8 mmol/l), and (V) Borg \nRPE scale (> 18/20) [30]. These criteria are used in a stand-\nardized way for athletes and helped as a reliable orienta-\ntion in this study [31]. The participants achieved maximum \nphysical load by obtaining a Borg RPE scale value of at \nleast 18 or more. Absolute and relative ­VO2peak 3   Differences in relative \n­VO2peak between the treadmill \nand the bicycle compared to \naverage measurements of each \nsubject. The black line refers to \na mean difference of 1.92 ml/\nmin/kg. Using an ANOVA, \na statistically significant \neffect was calculated for the \nwithin-subject factor method \n(cardiopulmonary exercise \ntesting: bicycle and tread-\nmill), F = 19.049, p = 0.000; \ni.e., p < 0.01. There was no \nsignificant effect with the inter-\naction method × sex (F = 0.630, \np = 0.438; i.e., p > 0.05)\n2395\nEuropean Journal of Pediatrics (2022) 181:2389–2397 European Journal of Pediatrics (2022) 181:2389–2397 2395 Fig. 2   Differences in maximum \nlactate between the treadmill \nand the bicycle compared \nto average measurements of \neach subject. The black line \nrefers to a mean difference \nof − 0.79 mmol/l. Using an \nANOVA, which did not show \nsignificant differences for the \nwithin-subject factor method \n(cardiopulmonary exercise \ntesting: bicycle and treadmill), \nF = 3.558, p = 0.076; i.e., \np > 0.05. There was also no \nsignificant effect with the inter-\naction method × sex (F = 0.000, \np = 0.983; i.e., p > 0.05) Fig. 2   Differences in maximum \nlactate between the treadmill \nand the bicycle compared \nto average measurements of \neach subject. The black line \nrefers to a mean difference \nof − 0.79 mmol/l. Using an \nANOVA, which did not show \nsignificant differences for the \nwithin-subject factor method \n(cardiopulmonary exercise \ntesting: bicycle and treadmill), \nF = 3.558, p = 0.076; i.e., \np > 0.05. There was also no \nsignificant effect with the inter-\naction method × sex (F = 0.000, \np = 0.983; i.e., p > 0.05) Interestingly, there were no significant differences \nbetween male and female participants, which comparable \nresults for ­HRmax, ­Lamax, and ­VO2peak/kg in both male and female participants. There are usually differences in gender- \nspecific athletic performances [39]. These results can \nbe explained by the homogeneity of the participants. Both, female participants. There are usually differences in gender- \nspecific athletic performances [39]. These results can \nbe explained by the homogeneity of the participants. Both, 1 3\nFig. 3   Differences in relative \n­VO2peak between the treadmill \nand the bicycle compared to \naverage measurements of each \nsubject. The black line refers to \na mean difference of 1.92 ml/\nmin/kg. Using an ANOVA, \na statistically significant \neffect was calculated for the \nwithin-subject factor method \n(cardiopulmonary exercise \ntesting: bicycle and tread-\nmill), F = 19.049, p = 0.000; \ni.e., p < 0.01. Absolute and relative ­VO2peak The mean RQ of our participants was, on \nthe BC 1.08 + / − 0.1 and 1.09 + / − 0.1 on the TM. Due to \nthe lack of regular physical training and low exercise level \nof our participants, these two criteria were fulfilled. The \nprevious study has found a lowered RERpeak in obese ado-\nlescents in contrast to lean adolescents [32]. Therefore, the \npresent study has proved that both CPETs can determine of \nmaximum physical load in children and adolescents with \nextreme obesity. Recent studies have shown that a supramax-\nimal validation test to confirm VO2max is unaffected by \nsex, cardiorespiratory fitness level, and especially body \nmass [33]. Regarding the maximum effort evaluation, these \nsupramaximal validation tests could be suitable for children \nand adolescents with extreme obesity. The main limitation of the present study was the modest \nnumber of participants due to the study being explorative in \nnature. Based on the inclusion criteria, only a few subjects \nwere eligible. The main issue with participant acquisition 1 3\nFig. 1   Differences in maximum \nheart rate between the treadmill \nand the bicycle compared \nto average measurements of \neach subject. The black line \nrefers to a mean to the mean \ndifference of 4.4 beats per \nminute. Consequently, using \nan ANOVA, a statistically \nsignificant effect was calculated \nfor the within-subject factor \nmethod (cardiopulmonary \nexercise testing: bicycle and \ntreadmill), F = 4.848, p = 0.041; \ni.e., p < 0.05. There was no \nsignificant effect for the interac-\ntion method × sex (F = 0.005, \np = 0.945; i.e., p > 0.05) 1 3 3 Interestingly, there were no significant differences \nbetween male and female participants, which comparable \nresults for ­HRmax, ­Lamax, and ­VO2peak/kg in both male and \nfemale participants. There are usually differences in gender- \nspecific athletic performances [39]. These results can \nbe explained by the homogeneity of the participants. Both, \nFig. 2   Differences in maximum \nlactate between the treadmill \nand the bicycle compared \nto average measurements of \neach subject. The black line \nrefers to a mean difference \nof − 0.79 mmol/l. Using an \nANOVA, which did not show \nsignificant differences for the \nwithin-subject factor method \n(cardiopulmonary exercise \ntesting: bicycle and treadmill), \nF = 3.558, p = 0.076; i.e., \np > 0.05. There was also no \nsignificant effect with the inter-\naction method × sex (F = 0.000, \np = 0.983; i.e., p > 0.05)\nFig. Absolute and relative ­VO2peak Dtsch Arztebl Int 115(24):409–416 6. Löllgen H, Leyk D (2018) Ergometrische Belastungsuntersuchun-\ngen in der Sportmedizin. Dtsch Arztebl Int 115(24):409–416 7. Hills AP, Andersen LB, Byrne NM (2011) Physical activity and \nobesity in children. Br J Sports Med 45(11):866–870. https://​\ndoi.​org/​10.​1136/​bjspo​rts-​2011-​090199f 7. Hills AP, Andersen LB, Byrne NM (2011) Physical activity and \nobesity in children. Br J Sports Med 45(11):866–870. https://​\ndoi.​org/​10.​1136/​bjspo​rts-​2011-​090199f Funding  Open Access funding enabled and organized by Projekt \nDEAL. 8. Alberga AS, Prud’homme D, Sigal RJ et al (2016) Effects of aero-\nbic training, resistance training, or both on cardiorespiratory and \nmusculoskeletal fitness in adolescents with obesity: the HEARTY \ntrial. 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BMJ Open 6(4):e010929. https://​doi.​org/​\n10.​1136/​bmjop​en-​2015-​010929 Ethics approval  Ethical approval was not sought for this study, as all \nparticipants received usual care diagnostics. Consent to participate  Informed consent was obtained from all par-\nticipants and parents before the study. 11. Hansen D, Marinus N, Remans M, Courtois I, Cools F, Calsius \nJ, Massa G, Takken T (2014) Exercise tolerance in obese vs. lean \nadolescents: a systematic review and meta-analysis. Obes Rev \n15(11):894–904. https://​doi.​org/​10.​1111/​obr.​12202 (Epub 2014 \nAug 6. PMID: 25132188) Consent for publication  Informed consent for publication was obtained \nfrom all participants and parents before the study. Conflict of interest  The authors declare no competing interests. Absolute and relative ­VO2peak There was no \nsignificant effect with the inter-\naction method × sex (F = 0.630, \np = 0.438; i.e., p > 0.05) 3 3 2396 European Journal of Pediatrics (2022) 181:2389–2397 the cross-sectional KiGGS Wave 2 study and trends. J Health Monit \n3(1):15–22. https://​edoc.​rki.​de/​handle/​176904/​5627f the cross-sectional KiGGS Wave 2 study and trends. J Health Monit \n3(1):15–22. https://​edoc.​rki.​de/​handle/​176904/​5627f females and males, were most likely unfamiliar with this \nkind of physical activity and reached a considerably lower \nmaximum power on BC performed by normal weight boys \n(3–4 W/kg) and girls (2.8–3.5 W/kg) [40]. 3. 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