Exercise and BMI z-score in Overweight and Obese Children and Adolescents: A Systematic Review and Network Meta-Analysis of Randomized Trials

Abstract

Aim: Examine the effects of selected types of exercise (aerobic, strength training, both) on BMI z-score in overweight and obese children and adolescents.

Methods: Randomized exercise intervention trials ≥ 4 weeks were included. Studies were retrieved by searching six electronic databases, cross-referencing and expert review. Dual selection and abstraction occurred. Risk of bias and confidence in cumulative evidence were assessed. Network meta-analysis was performed using multivariate random-effects meta-regression models while surface under the cumulative ranking curves were used to calculate a hierarchy of exercise treatments. The number needed to treat (NNT) and percentile improvement (U3 ) were also calculated.

Results: Thirty-four studies representing 2,239 participants were included. Median exercise occurred 3 times per week, 50 minutes per session over a 12-week period. Statistically significant reductions in BMI z-score were found for aerobic exercise and combined aerobic and strength exercise, but not strength training alone (M±SD, 95% CI: aerobic, -0.10, -0.15 to -0.05; aerobic and strength, -0.11, -0.19 to -0.03; strength, 0.04, -0.07 to 0.15). Combined aerobic and strength training was ranked best, followed by aerobic exercise and strength training. The NNT was 2 for both aerobic exercise and combined aerobic exercise and strength training. Percentile improvements were 28.8% for aerobic exercise and 31.5% for combined aerobic exercise and strength training. Confidence in effect estimates was ranked as low for aerobic exercise and very low for combined aerobic and strength training as well as strength training.

Conclusions: Aerobic exercise and combined aerobic exercise and strength training are associated with reductions in BMI z-score.

Keywords: adolescents; children; exercise; meta-analysis; obesity; overweight; systematic review.

Conflict of interest statement

Conflicts of Interest: None.

© 2016 Chinese Cochrane Center, West China Hospital of Sichuan University and John Wiley & Sons Australia, Ltd.

Figures

Figure 1

Flow diagram for selection of articles. *, number of reasons exceeds the number of articles because some articles were excluded for more than one reason.

Figure 2

Risk of Bias. Risk of bias based on Cochrane's Risk of Bias Assessment Instrument.

Figure 3

Network plot for study comparisons included in BMI z-score analysis. The nodes (circles) represent the different treatments while the edges (lines) represent the available direct comparisons between pairs of treatments. Both nodes and edges are weighted by the number of studies involved in each treatment and comparison, respectively.

Figure 4

Contribution plot for BMI z-score comparisons. The size of the squares are proportional to the percent contribution of the column-defining direct comparison to the row-defining network estimate. A = Control, B = Aerobic, C = Strength, D = Aerobic and Strength. Included Studies, number of observations (44) nested within studies (34).

Figure 5

Interval plot for changes in BMI z-score based on all pairwise comparisons. The black horizontal lines represent the confidence intervals while the red lines represent the prediction intervals. The number of observations for each comparison were 24 (Aerobic versus Control), 5 (Strength versus Control), 9 (Aerobic and Strength versus Control), 3 (Strength versus Aerobic), 2 (Aerobic and Strength versus Aerobic) and 1 (Aerobic and Strength versus Strength).

Figure 6

Network forest plot for changes in BMI z-score based on individual study results, grouped by treatment contrast and design. Markers for each point estimate are proportional to the inverse square of the standard error. Individual study results are shown as blue point estimates (squares) and 95% confidence intervals (lines), pooled estimates and 95% CIs within designs as hollow green diamonds, and overall pooled results and 95% CIs for each of the six treatment contrasts as hollow red diamonds. A = Control, B = Aerobic, C = Strength, D = Aerobic and Strength.

Figure 7

Funnel plot for small-study effects. A = Control, B = Aerobic, C = Strength, D = Aerobic and Strength.

Figure 8

Cumulative probability curves for the BMI z-score network showing the estimated and predictive probabilities for each treatment being up to a specific rank.