Author(s): LEDERGERBER, R., LICHTENSTEIN, E., FALK, B., FAUDE, O., Institution: UNIVERSITY OF BASEL, Country: SWITZERLAND, Abstract-ID: 1918

INTRODUCTION:
Maximal oxygen uptake (VO₂max) often increases in response to endurance training, but the magnitude of adaptation varies between individuals and appears to differ across developmental stages. A widespread view is that VO2max trainability is considerably lower in children than in adults. However, training load is usually not controlled and potential mechanisms for such a phenomenon remain unclear. Therefore, we aimed to quantify VO₂max trainability across development while accounting for training load in a systematic manner (preregistration-DOI: 10.17605/OSF.IO/V8UHT).
METHODS:
Following PRISMA-RR guidelines, we conducted a rapid systematic review with meta-analysis using MEDLINE. Peer-reviewed randomized controlled trials including healthy, normal-weight participants aged 6-40 years were eligible if relative VO₂max was directly measured by spiroergometry before and after a structured endurance training intervention. Standardized mean differences (Hedges’ g) of pre–post changes between intervention and control groups were computed. A random-effects meta-regression was performed with chronological age and training load (derived from reported intensity and duration using TRIMP) as moderators. Both linear and non-linear age effects were explored to identify the most appropriate model fit.
RESULTS:
From 4’669 screened records, 82 studies were included, yielding 91 intervention-control effect sizes. The best model fit was provided by a random-effects meta-regression including training load and a non-linear age term (natural spline, df = 3). Training load was a significant positive predictor of relative VO₂max adaptations (β = 0.124, SE = 0.034, p = 0.0002, per 1000 TRIMP). In contrast, the age-response relationship was shallow, with only weak evidence for non-linearity, indicating similar trainability from childhood to young adulthood.
CONCLUSION:
Training load appears to be the most important determinant of VO₂max adaptations across development, whereas age shows only a weak non-linear association. These findings challenge the prevailing view of markedly limited VO₂max trainability in youth and highlight the importance of precise quantification of training load when interpreting training responses. Future analyses will examine the influence of body size using allometric scaling and explore potential differences in endurance performance outcomes. Furthermore, we suggest that maturation status and investigation of dose-response relationships should be considered in future research.