School-Based Interventions to Improve Cardiorespiratory Fitness in Adolescents: Systematic Review with Meta-analysis

Background School-based intervention can contribute to the promotion of cardiorespiratory fitness (CRF) in adolescents. However, it is necessary to systematize how intervention strategies and the methodological characteristics of studies influence the effects of CRF interventions. Objective A meta-analysis review of school-based intervention studies aimed at increasing CRF in adolescents (10-19 years of age) was conducted. Methods A search for studies was conducted using the Medline, Web of Science, LILACS, PsycINFO, Embase, Scopus, SPORTDiscus and Cochrane databases and the reference lists of the selected studies. The peer selection process included consideration of school-based randomized or non-randomized controlled trials with a duration >= 12 weeks published in English, Portuguese or Spanish, and with some CRF measures. The methodological quality of the studies was also assessed. The standardized mean differences (SMDs) and 95 % confidence intervals ( 95 % CIs) were calculated as an effect measure. Results Forty publications of 30 interventions were included in the review, and 25 of these were meta-analysed. The effects of CRF interventions were moderate and significant (SMD = 0.68, 95 % CI 0.45-0.90), with high heterogeneity (I-2 = 97 %). The effect size varied significantly according to the age group, sample size, intervention environment, strategies in experimental groups, CRF priority in the study, CRF test and indicator, session length, weekly frequency, intervention duration and presentation of results by sex. Conclusion Interventions in the school environment seem to have a positive effect on CRF among adolescents, but there is high heterogeneity between studies. Some intervention characteristics can explain better effects on CRF (e.g. exercise sessions in addition to physical education classes; primary focus on this outcome; combination of aerobic and resistance exercises; classes lasting >= 60 min; frequency of three times weekly; and intensity control).