Background <p>Physical fitness is an important indicator of health during childhood and adolescence. Several components of physical fitness showed declining trends, with periods of acceleration or stabilisation depending on the component. Although Europe is the most studied continent, existing reviews have largely relied on single-test approaches or descriptive summaries, without simultaneously examining all health-related components, accounting for between-study variability analyses, or extending monitoring beyond 2014 to include the COVID-19 pandemic. This systematic review aims to analyse temporal trends of health-related components of physical fitness in European children and adolescents aged 6–16&#xa0;years, examining differences by sex and age groups.</p> Methods <p>A systematic search was conducted in PubMed, Web of Science, SPORTDiscus and Scopus up to December 2025. Eligible studies were conducted in European countries and included children and adolescents aged 6–16&#xa0;years, using repeated cross-sectional designs and reporting physical fitness components at two or more time points including sample sizes, means and standard deviations. Study quality was assessed with a modified Downs and Black checklist. Data were standardised into <i>z</i> scores based on sample-weighted means and standard deviations, considering the study, physical fitness component, sex and age. Linear mixed models were developed for each physical fitness component to estimate trends (linear, quadratic or cubic) and interactions by sex or age group.</p> Results <p>Thirty-eight studies were included, representing 417,362 children and adolescents, from 20 European countries between 1965 and 2023. Cardiorespiratory endurance increased until the 1980s, then declined with a deceleration between 2015 and 2023. Body composition decreased linearly up to 2022, more markedly among males. Upper-body strength declined from the 1970s to 2020s, stabilising between the 1980s and 2000s. Lower-body strength increased until the 1980s and declined until 2023. Flexibility declined continuously, with an accelerated decrease after the 2000s.</p> Conclusions <p>Health-related components of physical fitness showed persistent declines among European children and adolescents, with differences in the shape and magnitude of trends. These findings highlight the heterogeneity of the available evidence and the need for a standardised, valid and feasible European fitness test battery. Public initiatives should continue to promote adherence to physical activity guidelines, particularly muscle-strengthening recommendations.</p> Registration <p>PROSPERO ID: CRD42024609888.</p>