Reference Values of Aerobic Fitness in the Contemporary Paediatric Population
Condition: Healthy; Obese
Study type: Observational

Summary: 
      In most pediatric medical conditions, tremendous progress in pediatrics has significantly
      improved the overall prognosis and transferred the mortality from childhood to adulthood.
      Nevertheless, chronic diseases remain the leading cause of death and physical inactivity
      appears to be a major aggravating factor. Yet, a good physical activity has a positive impact
      on quality of life and prevents future health morbidities, such as obesity and cardiovascular
      disease. Therefore, after focusing on the survival of children with chronic diseases, more
      attention is being given to health-related quality of life and secondary prevention.

      In this context, the cardio-pulmonary exercise test (CPET), which is a non-invasive and
      dynamic examination, has become the gold standard to identify subjects with impaired physical
      capacity and to identify the causes of their limitations (muscular, cardiac, respiratory,
      behavioral, etc.). Moreover, CPET is the key examination to enroll patients in personalized
      physical rehabilitation programs (muscle deconditioning, respiratory limitation, etc.).

      Despite a growing interest in CPET and individualized rehabilitation programs for chronic
      diseases, the investigators still face the lack of reference values for pediatric CPET. In
      current practice, many CPET pediatric laboratories use the reference values of maximum oxygen
      uptake (VO2max) defined by Cooper et al. in 1984, from a cohort of 109 healthy children.
      However, their equations are linear and based on weight only. Non linear equations and the
      use of other anthropometric variables may be relevant in pediatrics. For instance, in the
      current era, normal CPET pediatric values should consider the prevalence of overweight and
      obesity in childhood general population (respectively 30% and 10% in Europa and 35% and 25%
      in North America), as well as in the population of children with chronic disease.

      In the past decade, our group has developed a research program on physical capacity in
      children, with a focus on pediatric CPET and physical rehabilitation, from a cohort of nearly
      1000 exercise tests in children. The lack of reliable pediatric reference values for VO2max,
      and all CPET variables as well, has become an important issue.

      In this study, the investigators aim to define pediatric reference CPET values from a large
      cohort of 6 to 17 year-old children, using several anthropometric variables to define the
      most appropriate Z-scores equations (part 1). The investigators will also validate the
      Z-scores equations using an independent population (part 2).
    

Detailed description: 
      This cross-sectional study included healthy children from 6 to 17 years old and obese
      children with no other comorbidities other than those due to metabolic syndrome
      (hypertension, dyslipidemia, type 2 diabetes sleep apnea, hepatic steatosis). Patients refuse
      the use of medical data will be excluded.

      Part 1 - Z-score equations: After description of the study sample, the regression method will
      be identified (linear, polynomial, logarithmic, spline, etc.). The main anthropometric
      determinants (age, gender, height, weight, BMI) will be tested, and the mathematical models
      that best fit to the data will be identified (use of the adjusted coefficient of
      determination R2). The models will calculate, for each subject, the difference between the
      value predicted by the model and the value actually observed (residuals of the model). The
      occurrence of heteroscedasticity (e.g. the circumstance in which the variability of a
      variable is unequal across the range of values of a second variable that predicts it) will be
      tested. The Z-scores will be measured by the difference between predicted values and observed
      values divided by the calculated standard deviation.

      Part 2- Validation of Z-score equations from an independent population The validity of the
      Z-score equations will be tested on a cohort of 100 pediatric in 6 to 18 year-old children,
      from pediatric CPET laboratories that did not participate in the part 1 study. The CPET
      variables may be retrospectively collected from existing database or prospectively collected,
      but no CPET should be performed for the only purpose of the research (observational study)
    

Observational model: Cohort
Time perspective: Retrospective
Sampling method: Non-Probability Sample
Study population: 
        Healthy children cohort consisted of children referred to a paediatric cardiologist for a
        nonsevere functional symptom related to exercise (murmur, palpitation, chest pain, and
        dyspnoea) or for a medical sports certificate. Obese children cohort consisted of children
        with BMI > 85e percentile referred to a paediatric cardiologist for checkup.
      
Keywords: Cardiopulmonary exercise test; Z score; Pediatric; VO2max; VE/VCO2 slope