Meeting the 24-Hour Movement Guidelines (physical activity, screen time, and sleep duration) has been associated with positive health indicators. However, there are no previous meta-analyses that have examined the overall adherence to the 24-Hour Movement Guidelines from pre-school to adolescence across the world. Therefore, the main purpose of this systematic review and meta-analysis was to examine the overall (non)adherence to the 24-Hour Movement Guidelines among preschoolers, children, and adolescents worldwide. Four electronic databases (MEDLINE, Scopus, Web of Science, and Cochrane Database of Systematic Reviews) were searched for quantitative studies published in Spanish and English between January 2016 and May 2021. Studies that were conducted with apparently healthy participants and reported the overall (non)adherence to the 24-Hour Movement Guidelines in preschoolers and/or children and/or adolescents were included. Sixty-three studies comprising 387,437 individuals (51% girls) aged 3–18 years from 23 countries were included. Overall, 7.12% (95% confidence interval (95%CI): 6.45%–7.78%) of youth met all three 24-Hour Movement Guidelines, and 19.21% (95%CI: 16.73%–21.69%) met none of the 3 recommendations. Concerning sex, adherence to all recommendations was significantly lower in girls (3.75%, 95%CI: 3.23%–4.27%) than in boys (6.89%, 95%CI: 5.89%–7.89%) (p < 0.001). However, there were no sex differences regarding adherence to any of the 3 individual recommendations (girls, 15.66%, 95%CI: 8.40%–22.92%; boys, 12.95%, 95%CI: 6.57%–19.33%). In terms of age group, adherence to the 3 recommendations was 11.26% (95%CI: 8.68%–13.84%), 10.31% (95%CI: 7.49%–13.12%), and 2.68% (95%CI: 1.78%–3.58%) in preschoolers, children, and adolescents, respectively. Conversely, 8.81% (95%CI: 5.97%–11.64%) of preschoolers, 15.57% (95%CI: 11.60%–19.54%) of children, and 28.59% (95%CI: 22.42%–34.75%) of adolescents did not meet any of the recommendations. South America was the region with the lowest adherence (all: 2.93%; none: 31.72%). Overall adherence to the 24-Hour Movement Guidelines was positively related to country Human Development Index (β = –0.37, 95%CI: –0.65 to –0.09; p = 0.010). Most young people fail to meet the three 24-Hour Movement Guidelines, particularly adolescents, girls, and those who are from countries with a lower Human Development Index. Moreover, 1 in 5 young people did not meet any of these recommendations. Therefore, these results highlight the need to develop age- and sex-specific strategies to promote these movement behaviors from the early stages of life.

Cardiorespiratory fitness (CRF) reflects the integrated ability to transport oxygen from the atmosphere to the mitochondria to perform physical work and thus reflects the overall capacity of the cardiovascular and respiratory systems and the ability to perform prolonged exercise. ¹ An increasing body of epidemiological and clinical evidence demonstrates that low levels of CRF are associated with a high risk of cardiovascular disease, all-cause mortality, and various cancers. ²