Reference values of aerobic fitness in the contemporary paediatric population

Abstract

Aims There has been a growing interest in the use of markers of aerobic physical fitness (VO2max assessed by cardiopulmonary exercise testing (CPET)) in the follow-up of paediatric chronic diseases. The dissemination of CPET in paediatrics requires valid paediatric VO2max reference values to define the upper and lower normal limits. This study aimed to establish VO2max reference Z-scores values, from a large cohort of children representative of the contemporary paediatric population, including those with extreme weights. Methods and results In this cross-sectional study, 909 children aged 5 to 18-years-old from the general French population (development cohort), and 232 children from the general German and US populations (validation cohort) underwent a CPET, following the guidelines on high-quality CPET assessment. Linear, quadratic, and polynomial mathematical regression equations were applied to identify the best VO2max Z-score model. Predicted and observed VO2max values using the VO2maxZ-score model, and the existing linear equations were compared, in both development and validation cohorts. For both sexes, the mathematical model using natural logarithms of VO2max, height, and BMI was the best fit for the data. This Z-score model could be applied to normal and extreme weights and was more reliable than the existing linear equations, in both internal and external validity analyses (https://play.google.com/store/apps/details?id=com.d2l.zscore). Conclusion This study established reference Z-score values for paediatric cycloergometer VO2max using a logarithmic function of VO2max, height and BMI, applicable to normal and extreme weights. Providing Z-scores to assess aerobic fitness in the paediatric population should be useful in the follow-up of children with chronic diseases.

Reference values of cardiopulmonary exercise test parameters in the contemporary paediatric population

“…From a cohort of 909 healthy children aged 5 to 18 years who underwent a cycloergometer CPET, this study de ned paediatric reference Z-score values of the main paediatric CPET parameters, apart from VO 2max , whose reference values were recently reported by our group. [11] These paediatric CPET reference values were generated using the best mathematical model (linear, quadratic, or polynomial) for the Z-score construction, according to the main anthropometric predictors (sex, age, height, weight, and BMI), to apply to normal and extreme weights. This paediatric cohort is representative of the general contemporary paediatric population, with a balanced sex ratio and a 25%proportion of overweight or obese children, [32] and had recently undergone external validation from a CPET cohort of 232 German and American healthy children.…”

“…This paediatric cohort is representative of the general contemporary paediatric population, with a balanced sex ratio and a 25%proportion of overweight or obese children, [32] and had recently undergone external validation from a CPET cohort of 232 German and American healthy children. [11] This study intended to satisfy a high methodological quality level and ful lled 11 of the 14 criteria from the ATS/ACCP statement on cardiopulmonary exercise testing. [19] In terms of maximal CPET parameters, the existence of Z-scores for the main maximum parameters will improve discussions on maximality criteria in paediatric CPET.…”

“…The maximal CPET parameters included: (1) the maximal heart rate; (2) the maximal respiratory exchange ratio (RER max ), which corresponds to the ratio of CO 2 elimination (VCO 2 ) and oxygen uptake (VO 2 ); (3) the maximum workload in Watts (maintained for at least 30 seconds by the patient); (4) and the maximum oxygen pulse (O 2 pulse max ), e.g., a surrogate of stroke volume at peak exercise, which corresponds to the ratio between VO 2max and maximal heart rate. [19] The submaximal CPET parameters included: (1) the VAT, e.g., the point at which minute ventilation increases disproportionally relative to VO 2 , which re ects muscular response to exercise [2,25], and manually calculated by a single investigator using V-slope method [26] and expressed as a percentage of the predicted VO 2max (%-predicted VAT); [11] (2) the VE/VCO 2 slope, e.g., an indicator of ventilation-perfusion ratio during exercise, [27,28] calculated from breathby-breath data using linear regression of minute ventilation (VE) and CO 2 production (VCO 2 ) obtained during incremental exercise (VE = [VE/VCO 2 slope] × VCO 2 + b) [13], and measured from the beginning of incremental exercise (after the warm-up period) to maximum exercise (or respiratory compensation point when present); [2,27] (3) and the OUES, e.g., a submaximal surrogate parameter of VO 2max , calculated from breath-by-breath data using linear regression of VO 2 on logarithmically converted VE (VO 2 = OUES × log 10 VE + b), measured from the beginning of the exercise test to its maximal point, and expressed as a weight-normalized value (OUES Kg ). [14] The ventilatory parameters included: (1) the maximum tidal volume (VT max ), which corresponds to the patient's inspiratory volume for each breath at maximum effort averaged over 30 seconds; [19] (2) the maximum respiratory rate (RR max ), which corresponds to the respiratory rate averaged over 30 seconds at maximum effort; [19] (3) the breathing reserve (BR), calculated using the formula BR (%) = [MVV-VE max ] ÷ MVV*100 (with MVV, maximal voluntary ventilation = 35*FEV1); [19] (4) the maximum ventilatory equivalent for CO 2 (VEqCO 2max ) which corresponds to the ratio between VE and VCO 2 averaged over 30 seconds at maximum effort; [29] and (5) the maximum ventilatory equivalent for O 2 (VEqO 2max ) which corresponds to the ratio between the VE and the VO 2 averaged over 30 seconds at maximum effort.…”

“…Reference values were not analysed in function of other parameters in uencing physical capacity, such as lean mass, pubertal status, or the level of physical activity, as in the study on paediatric VO 2max reference Z-scores. [11] The impact of ethnic variation on body fat and muscle mass has not been investigated because of restrictive regulations on the assessment of ethnicity in paediatric clinical research. Moreover, the children included in this study were not communitybased, as we were concerned that if we had drawn lots of schools to identify volunteers to perform a CPET, a large proportion of child volunteers would have been athletes.…”

“…The VO 2max reference values de ned by , are based on linear equations from a small cohort of 109 healthy children with normal weight and are currently less adapted to the contemporary paediatric population [9,10]. Our group recently established reference Z-score values for paediatric cycloergometer VO 2max , applicable to normal and extreme weights, from a cohort of 1141 healthy children, including 909 children in the development cohort and 232 children in the validation cohort [11]. For both sexes, the Z-score equations were modelled with a logarithmic function of VO 2max , height, and BMI.…”