Is the type of school uniform linked with physical activity levels and physical fitness in schoolchildren? A systematic review covering 1,098,972 children and adolescents

School uniforms play a crucial role in promoting physical activity among children and adolescents during school hours. This increased activity can help reduce the risk of metabolic and non-communicable diseases, with physical inactivity and a sedentary lifestyle acting as mediators in the development of these conditions. This systematic review aimed to explore the differences in physical activity levels and physical fitness based on the type of uniform worn by schoolchildren. The search strategy was performed in eight databases—PubMed, Web of Science, SPORTDiscus, ScienceDirect, Embase, CINAHL, Scopus, and LILACS—following PRISMA guidelines. They were selected on the basis of the following criteria: they were children and adolescents in school and used traditional schools or sports uniforms with their levels of physical activity and physical condition. Additionally, a manual search was performed on Google Scholar to include gray literature. From 1,703 initially identified studies, five studies met inclusion criteria. Sports uniforms were generally associated with higher physical activity levels compared to traditional uniforms, with girls showing 14.5 additional minutes of playtime and significantly greater activity during recess and lunch periods (p < 0.05). Two studies demonstrated improved cardiorespiratory and muscular fitness indicators in adolescents wearing sports uniforms. Population-level data from 135 countries confirmed these individual-level findings, showing reduced physical activity compliance in countries with mandatory traditional uniform policies. The available scientific evidence suggests that sports uniforms facilitate higher levels of physical activity, increased playtime, and improved physical fitness indicators among school-aged children and adolescents, with particularly pronounced benefits for girls. Schools should consider adopting more flexible uniform policies that prioritize comfort and movement to support students' overall health outcomes. PROSPERO CRD42024571665.