title: The impact of long-term school-based physical activity interventions on body mass index of primary school children - a meta-analysis of randomized controlled trials.
abstract: BACKGROUND
  Physical activity (PA) intervention is a commonly recommended strategy to combat childhood obesity. However, its effectiveness has long been controversial. This paper aims to examine the effectiveness of long-term (≥12 months) school-based PA interventions on body mass index (BMI) in primary school children, who are gaining BMI.
  
  
  METHODS
  Original papers were retrieved from PubMed, Google Scholar, the Cochrane Library and Web of Science, published between 1990 and 2015. The inclusion criteria were those research studies that were: randomized controlled trials (RCTs), conducted in primary school settings, had valid data on BMI at baseline and at the final follow up (or on BMI changes), and involved PA intervention that lasted for at least 12 months.
  
  
  RESULTS
  Out of 11,158 potentially eligible articles, 18 papers were included in the analysis, involving 22,381 primary school children with intervention durations ranging from 12 to 72 months. Compared to the control groups, the BMI increment was 2.23 kg/m(2) less in the intervention groups (p < 0.05). The heterogeneity was high across the studies (99.8 %), but declined after sub-group analyses. The intervention type, intervention duration, and weekly PA intervention time were among the factors leading to the heterogeneity.
  
  
  CONCLUSIONS
  Long-term school-based interventions containing PA as a core component appear to be effective in achieving healthier BMI. However, the results should be interpreted with caution due to the high heterogeneity among the studies. More high quality school-based RCTs among diverse populations are needed to improve the homogeneity and to yield a more robust conclusion.
authors.affiliation: Department Woman and Child's Care and Adolescent Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Rd., Wuhan, 430030, Hubei, P.R. China. annymei2012@gmail.com.
authors.forename: Hong
authors.initials: H
authors.lastname: Mei
authors.affiliation: Department Woman and Child's Care and Adolescent Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Rd., Wuhan, 430030, Hubei, P.R. China. 1158528817@qq.com.
authors.forename: Yuelin
authors.initials: Y
authors.lastname: Xiong
authors.affiliation: Department Woman and Child's Care and Adolescent Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Rd., Wuhan, 430030, Hubei, P.R. China. 1002824202@qq.com.
authors.forename: Shuixian
authors.initials: S
authors.lastname: Xie
authors.affiliation: Department Woman and Child's Care and Adolescent Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Rd., Wuhan, 430030, Hubei, P.R. China. 460462716@qq.com.
authors.forename: Siyu
authors.initials: S
authors.lastname: Guo
authors.affiliation: Department Woman and Child's Care and Adolescent Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Rd., Wuhan, 430030, Hubei, P.R. China. lykzjs@163.com.
authors.forename: Yukun
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department Woman and Child's Care and Adolescent Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Rd., Wuhan, 430030, Hubei, P.R. China. 418412217@qq.com.
authors.forename: Bingbing
authors.initials: B
authors.lastname: Guo
authors.affiliation: Department Woman and Child's Care and Adolescent Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Rd., Wuhan, 430030, Hubei, P.R. China. jd_zh@hust.edu.cn.
authors.forename: Jianduan
authors.initials: J
authors.lastname: Zhang
mesh_terms: D015992:Body Mass Index; D002648:Child; D006801:Humans; D009043:Motor Activity; D063766:Pediatric Obesity / Q000517:prevention & control*; D015397:Program Evaluation; D016032:Randomized Controlled Trials as Topic; D012572:School Health Services; D012574:Schools; D013997:Time Factors