Secular trends in physical activity in adolescents: A systematic review.

Objective: One in five adolescents has been estimated to perform sufficient physical activity (PA), thus potentially indicating that PA among adolescents has declined. This systematic review was aimed at reporting and summarizing the available knowledge regarding PA secular trends in adolescents over time. Methods: Seven databases were consulted (Web of Science, Scopus/Elsevier, Medline/PubMed, ScienceDirect, Lilacs, Physical Education Index, and SPORTDiscus), and 1809 studies were examined. According to the PRISMA guidelines, relevant research on secular PA trends in adolescents was screened for inclusion in a narrative synthesis. The risk of bias in the articles included was also assessed. Results: Forty-three studies with data collected between 1969 and 2018 met the inclusion criteria, and data from high-income countries predominated. PA was estimated predominantly by self-reporting, except in seven studies, and diverse contexts and domains were analyzed. Increased PA was reported in 16 studies (from 2.9% to 43.5%), decreased PA was reported in 15 studies (-2.5% to -69.5%), and no change was reported in 22 studies (-12.0% to 14.4%). Conclusions: Although PA has increased in some countries, very little information is available in low- and middle-income countries. Efforts should support studies on PA trends in adolescents from economically disadvantaged countries.