Koble K; Technical University Munich, Munchen, Germany.
Willinger L; Engl T; Muhlbauer F; Huber S; Dettenhofer M;
Oberhoffer R

International journal of sports physiology & performance. 21(6):748-757,
2026 Jun 01.

PURPOSE: While the development of cardiorespiratory fitness in normally
active children and adolescents is well-documented, longitudinal data on
physiological adaptations to training in youth athletes remain limited.
This study aimed to investigate the long-term development of
cardiorespiratory fitness in young competitive athletes over a period of
2-6 years.

METHODS: A total of 397 young athletes (48 girls), aged 8-20 years, from
a variety of sports underwent up to 6 repeated assessments between 2012
and 2024. Peak exercise performance (Wmax) and peak aerobic power
(VO2peak), both were measured via cardiopulmonary exercise testing on an
electronically braked cycle ergometer. A linear mixed model analysis was
used to evaluate longitudinal changes in VO2peak and Wmax (both normalized
to body mass), including body surface area and training intensity
(MET-hours/week) as fixed effects, with sex-stratified analyses.

RESULTS: A total of 1009 cardiopulmonary exercise testing were analyzed.
At baseline, boys showed higher age-specific VO2peak and Wmax, while girls
had higher age-specific VO2peak despite similar training intensity.
Longitudinally, VO2peak increased significantly with age in mid-adolescent
girls and boys, particularly in endurance athletes, and was positively
associated with training intensity. Wmax rose with age but was less
influenced by training or sport type, showing a stronger relationship with
growth-related factors like body surface area.

CONCLUSIONS: VO2peak development in youth athletes is influenced by age,
body size, training intensity, and sport type, making it a sensitive
marker of aerobic adaptation. In contrast, Wmax reflects primarily
maturational growth and is less responsive to training-specific factors.