Effects of Physical Activity Interventions on Anthropometric, Body Composition, and Physical Fitness Indicators in Chilean Children and Adolescents: Systematic Review and Meta-Analysis

Background/Objectives: Physical activity interventions are widely implemented to promote health during childhood and adolescence; however, their effects on anthropometric, body composition, and physical fitness outcomes among Chilean pediatric populations remain unclear. This systematic review and meta-analysis aimed to determine the effects of physical activity interventions on these outcomes in Chilean children and adolescents. Methods: PubMed, Scopus, and Web of Science were systematically searched from inception to 30 May 2026, supplemented by Google Scholar and reference-list screening. The review followed the PRISMA 2020 guidelines and Cochrane recommendations and was registered in PROSPERO (CRD42023398677). Random-effects meta-analyses were conducted using standardized mean differences (SMDs) and 95% confidence intervals (CIs). Results: Eighteen studies involving participants aged 2–19 years were included, of which 16 contributed data to the meta-analysis. Pooled estimates favored physical activity interventions for cardiorespiratory fitness (SMD = 0.76; 95% CI: 0.48 to 1.04; I2 = 73.2%), body fat percentage (SMD = −0.83; 95% CI: −1.37 to −0.29; I2 = 84.9%), and triceps skinfold thickness (SMD = −0.14; 95% CI: −0.20 to −0.08; I2 = 0%). No clear difference was observed for waist circumference (SMD = −0.05; 95% CI: −0.14 to 0.05) or for BMI in studies with a concurrent control group (SMD = −0.37; 95% CI: −0.79 to 0.05) and in uncontrolled before–after studies (SMD = −0.13; 95% CI: −0.34 to 0.09). Between-study heterogeneity was substantial to considerable for most outcomes, and the certainty of evidence was very low for all meta-analyzed outcomes. Conclusions: Physical activity interventions were associated with more favorable pooled estimates for cardiorespiratory fitness and specific measures of adiposity among Chilean children and adolescents, whereas no clear differences were observed in BMI or waist circumference. However, substantial between-study heterogeneity and very low certainty of evidence limit confidence in these findings and warrant cautious interpretation. Further well-designed randomized controlled trials are needed to clarify these associations.