Effect of a school-based intervention on physical activity: cluster-randomized trial.
Physical activity in childhood has many health benefits; however, the majority of children in many countries, including Mexico, are insufficiently active. The objective of this investigation was to test the effect of a school-based environmental intervention on the physical activity and physical fitness of students attending public primary schools in Mexico City. Twenty-seven schools were randomly assigned to basic or plus intervention or control. The basic and plus groups were exposed to school environment and policy changes to enhance physical activity. Physical activity was evaluated in 699 randomly selected fourth- and fifth-grade students by measuring school-day and all-day (24 h) steps using pedometers worn for 5 d before and after the 6-month intervention. Physical fitness was assessed by measuring the 9-min run, flexibility, and sit-ups. We calculated the average change in school-day and all-day steps and fitness measures from baseline to follow-up. Using linear regression, we tested the effect of intervention on change controlling for baseline measures and covariates and accounting for the design effect of school. Using logistic regression, we tested the effect of intervention on reaching step cutoffs at baseline and follow-up. The plus group significantly (P < 0.05) increased school-day steps relative to control (change = 687 vs -639). Significantly (P < 0.05) more participants in the basic (25.8%) and plus (36.4%) groups reached step cutoffs during school relative to control (12.0%). The basic group significantly (P < 0.05) increased all-day steps relative to control (change = 581 vs -419). The plus group significantly (P = 0.05) increased sit-ups relative to control (change = 0.3 vs -1.7). A school-based environmental intervention improved student physical activity during school in public schools in Mexico City.