Development and Trainability of Cardiorespiratory Fitness Across Childhood and Adolescence

Abstract

Cardiorespiratory fitness (CRF) is a central determinant of health, performance, and resilience across the lifespan. Its development during childhood and adolescence reflects a complex interplay between growth, biological maturation, habitual activity and training. Understanding how CRF evolves and how it can be enhanced through training is fundamental for optimising youth development, promoting long-term health.

Longitudinal research indicates that CRF increases steadily from early childhood to mid-adolescence (Ingvarsdottir et al., 2024). These developmental patterns are strongly sex- and maturation-dependent: boys typically show a steeper rise and higher peak in maximal oxygen uptake (VO₂max) and endurance performance, mainly due to pubertal increases in muscle mass, cardiac output, and haemoglobin concentration, whereas girls experience relatively attenuated improvements due to greater fat mass accretion (Ingvarsdottir et al., 2024). Nevertheless, interindividual variability is substantial. Distinct developmental trajectories emerge depending on early-life activity levels, adiposity, and intrinsic aerobic capacity (de Fátima Guimarães et al., 2023), highlighting that maturation provides only the physiological framework for improvement, whereas behavioural engagement determines the realised potential.

The trainability of CRF during growth is well documented but highly dependent on maturational status. Aerobic and high-intensity training interventions in children and adolescents consistently yield meaningful improvements in endurance performance. However, recent large-scale meta-analytic evidence quantifies a distinct trainability gap between children and adults. Across more than 650 studies, children’s mean VO₂max training response amounted to ~58 % of the adult adaptation (Dotan, 2025), although high intensities were more effective. According to Dotan (2025), this attenuated responsiveness likely reflects neuromuscular rather than cardiovascular limitations – specifically, a reduced capacity to recruit high-threshold motor units. With advancing maturation, endocrine changes and neuromuscular efficiency might enhance these mechanisms, closing the trainability gap.

While this synthesis of studies is an important foundation, it lacks a systematic literature search and does not account for moderating factors such as training load or the allometric scaling of VO₂max adaptations (Dotan, 2025). This is why we are currently addressing these issues in a systematic review with meta-analysis, where preliminary findings will be presented in the symposium.

By integrating developmental, physiological, and methodological perspectives, this work aims to clarify whether the apparent child–adult differences in VO₂max trainability reflect true biological constraints or analytical artefacts. Understanding these mechanisms will contribute to a more accurate framework of aerobic adaptation across growth and maturation, guiding age-appropriate training strategies and informing evidence-based approaches to promote lifelong fitness and health.

References

de Fátima Guimarães, R., Barnett, T. A., Reid, R. E. R., Tremblay, A., Henderson, M., & Mathieu, M. E. (2023). Trajectories of cardiorespiratory fitness from childhood to adolescence: Findings from the QUALITY cohort. Journal of Sports Sciences, 41(9), 895–902. https://doi.org/10.1080/02640414.2023.2245262

Dotan, R. (2025). Children’s VO₂max trainability deficit: A quantitative analysis and a qualitative hypothesis. European Journal of Applied Physiology, 125, 2329–2351. https://doi.org/10.1007/s00421-025-05778-2

Ingvarsdottir, T.H., Johannsson, E., Rognvaldsdottir, V., Stefansdottir, R.S., Arnardottir, N.Y. (2024) Longitudinal development and tracking of cardiorespiratory fitness from childhood to adolescence. PLoS ONE, 19(3), e0299941. https://doi.org/10.1371/journal.pone.0299941