Cardiorespiratory fitness (CRF) reflects the integrated ability to deliver oxygen from the atmosphere to the skeletal muscles and to utilize it to generate energy to support muscle activity during exercise. Peak oxygen uptake (VO2) is internationally recognized as the criterion measure of youth CRF. It is well-documented that in youth peak VO2 increases with sex-specific, concurrent changes in a range of age- and maturity status-driven morphological and physiological covariates with the timing and tempo of changes specific to individuals. However, a recent resurgence of interest in predicting peak VO2 from field test performances and the persistence of fallacious interpretations of peak VO2 in 1:1 ratio with body mass have obfuscated general understanding of the development of CRF. Moreover, as spurious relationships arise when ratio-scaled data are correlated with health-related variables the use of this scaling technique has confounded the relationship of youth CRF with indicators of current and future health. This paper reviews the extant evidence and concludes that the interpretation of youth CRF and the promotion of young people’s health and well-being should be founded on scientific facts and not on fictions based on flawed methodology and specious interpretation of data.


Adolescents Children Clinical red flags Health and well-being Peak oxygen uptake 20 metre shuttle run


  1. N. Armstrong, A.M. McManus, Aerobic fitness, In: N. Armstrong, W. van Mechelen, [eds) Oxford textbook of children’s sport and exercise medicine 3rd edition, Oxford, Oxford University Press; 2017: 161-180.
  2. N. Armstrong, Commentary on the assessment and interpretation of pediatric aerobic fitness – the year that was 2017, Pediatric Exercise Science, 30 (2018) 12-18.
  3. A. Eliakim, B. Falk, N. Armstrong, F. Baptist, D.G. Behm, N. Dror, A.D. Faigenbaum, K.F. Janz, J. Jürimäe, A.L. McGowan, D. Nemet, P.T. Pianosi, M.B. Pontifex, S. Radom-Aizik, T. Rowland, A.V. Rowlands, Expert’s choice; 2018’s most exciting research in the field of pediatric exercise science, Pediatric Exercise Science, 31 (2019) 1-27.
  4. N. Armstrong, J. Welsman, Sex-Specific longitudinal modeling of youth peak oxygen uptake, Pediatric Exercise Science, 31 (2019) 204-212.
  5. B. Falk, R. Dotan, Measurement and interpretation of maximal aerobic power in children, Pediatric Exercise Science, 31 (2019) 144-151.
  6. N. Armstrong, J.R. Welsman, Assessment and interpretation of aerobic fitness in children and adolescents, Exercise and Sport Sciences Reviews, 22 (1994) 435-476.
  7. N.Armstrong, W. Van Mechelen, (2017) Oxford textbook of children's sport and exercise medicine, Oxford University Press.
  8. R.J. Winsley, J. Fulford, A.C. Roberts, J.R. Welsman, N. Armstrong, Sex difference in peak oxygen uptake in prepubertal children, Journal of Science and Medicine in Sport, 12 (2009) 647- 651.
  9. N. Armstrong, J.R. Welsman, Peak oxygen uptake in relation to growth and maturation in 11–17-year-old humans. European Journal of Applied Physiology, 85 (2001) 546-551.
  10. J.M. Tanner, Fallacy of per-weight and persurface area standards and their relation to spurious correlation, Journal of Applied Physiology, 2 (1949) 1-15.
  11. J. R. Welsman, N. Armstrong, Interpreting exercise performance in relation to body size, In: N. Armstrong, W. van Mechelen, (eds) Paediatric exercise science and medicine. 2nd edition, Oxford, Oxford University Press; 2008: 13-21.
  12. J. Welsman, N. Armstrong, Interpreting aerobic fitness in youth: The fallacy of ratio scaling, Pediatric Exercise Science, 31 (2019) 184-190.
  13. N. Armstrong, J. Welsman, Development of peak oxygen uptake from 11-16 years determined using both treadmill and cycle ergometry, European Journal of Applied Physiology, 119 (2019) 801-812.
  14. S. Mintjens, M.D. Menting, J.G. Daams, M.N.M. van Poppel, T.J. Roseboom, R.J.B.J. Gemke, Cardiorespiratory fitness in childhood and adolescence affects future cardiovascular risk factors: A systematic review of longitudinal studies, Sports Medicine, 48 (2018) 2577-2605.
  15. M. Loftin, M. Sothern, T. Abe, M. Bonis, Expression of V̇O2peak in children and youth with special reference to allometric scaling, Sports Medicine, 46 (2016) 1451-1460.
  16. D. Mayorga-Vega, P. Aguiler-Soto, J. Viciana Criterion-related validity of the 20-m shuttle run test for estimating cardiorespiratory fitness: A meta-analysis, Journal of Sports Science and Medicine, 14 (2015) 536-547.
  17. G.R. Tomkinson, J.J. Lang, J. Blanchard, L. Leger, M.S. Tremblay, The 20-m shuttle run: assessment and interpretation of data in relation to youth aerobic fitness and health, Pediatric Exercise Science, 31 (2019) 152-163.
  18. F.B. Ortega, E.G. Artero, J.R. Ruiz, G. VicenteRodriguez, P. Bergman, M. Hagstrӧmer, C. Ottevaere, E. Nagy, O. Konsta, J.P. Rey-López, A. Polito, S. Dietrich, M. Plada, L. Béghin, Y. Manios, M. Sjöström, M.J. Castillo, Reliability of health-related physical fitness tests in European adolescents: The HELENA study, International Journal of Obesity, 32 (2008) 49- 57.
  19. A.M. Machado-Rodrigues, N. Leite, M.J. Coelhoe-Silva, R.A. Martins, J. Valente-dos-Santos, L.P.G. Mascarenhas, M.C. Boguszewski, C. Padez, R.M. Malina, Independent association of clustered metabolic risk factors with cardiorespiratory fitness in youth aged 11–17 years, Annals of Human Biology, 41 (2014) 271- 276.
  20. G.R. Tomkinson, J.J. Lang, M. Tremblay, Temporal trends in the cardiorespiratory fitness of children and adolescents representing 19 high-income and upper middle-income countries between 1981 and 2014, British Journal of Sports Medicine, 53 (2017) 478-486.
  21. N. Armstrong, G. Tomkinson, U. Ekelund, Aerobic fitness and its relationship to sport, exercise training and habitual physical activity during youth, British Journal of Sports Medicine, 45 (2011) 849-858.
  22. M. Mountjoy, L.B. Andersen, N. Armstrong, S. Biddle, C. Boreham, H.P.B. Bedenbeck, U. Ekelund, L. Engebretsen, K. Hardman, A.P. Hills, S. Kahlmeier, S. Kriemler, E. Lambert, A. Ljungqvist, V. Matsudo, H. McKay, L. Micheli, R. Pate, C. Riddoch, P. Schamasch, C.J. Sundberg, G. Tomkinson, E. van Sluijs, W. van Mechelen, International Olympic Committee consensus statement on the health and fitness of young people through physical activity and sport, British Journal of Sports Medicine, 45 (2011) 839-848.
  23. M. Goran, D.A. Fields, G.R. Hunter, S.L. Herd, R.L. Weinster, Total body fat does not influence maximal aerobic capacity, International Journal of Obesity, 24 (2000) 841-848.
  24. G.R. Tomkinson, J.J. Lang, M.S. Tremblay, M. Dale, A.G. LeBlanc, K. Belanger, F.B. Ortega, L. Léger, International normative 20 m shuttle run values from 1,142,026 children and youth representing 50 countries, British Journal of Sports Medicine, 51 (2017) 1545-1554.
  25. C. Cadenas-Sanchez, T. Intemann, I. Labayen, A.B. Peinado, J. Vidal-Conti, J. Sanchis-Moysie, et al. Physical fitness reference standards for preschool children: The PREFIT project, Journal of Science and Medicine in Sport, 22 (2019) 430- 437.
  26. J.J. Lang, M.S. Tremblay, L. Leger, T. Olds, G.R. Tomkinson, International variability in 20m shuttle run performance in children and youth: who are the fittest from a 50-country comparison? A systematic literature review with pooling of aggregate results, British Journal of Sports Medicine, 52 (2018) 276.
  27. J.J. Lang, G.R. Tomkinson, I. Janssen, J.R. Ruiz, F.B. Ortega, L. Léger, M.S. Tremblay, Making a case for cardiorespiratory fitness surveillance among children and youth, Exercise and Sport Sciences Reviews, 46 (2018) 66-75.
  28. J.J. Lang, K Belanger, V. Poitra, I. Janssen, G.R. Tomkinson, M.S. Tremblay, Systematic review of the relationship between 20 m shuttle run performance and health indicators among children and youth, Journal of Science and Medicine in Sport, 21 (2017) 383-397.
  29. J.J. Lang, E.W. Phillips, H.M. Orpana, M.S. Tremblay, R. Ross, F.B. Ortega, et al. Field-based measurement of cardiorespiratory fitness to evaluate physical activity interventions, Bulletin of the World Health Organization, 96 (2018) 794-796.
  30. J.R. Ruiz, I. Cavero-Redondo, F.B. Ortega, G.J. Welk, L.B. Andersen, V. Martinez-Vizcaino, Cardiorespiratory fitness cut points to avoid cardiovascular disease risk in children and adolescents; what level of fitness should raise a red flag? A systematic review and metaanalysis, British Journal of Sports Medicine, 50 (2016) 1451-1458.