Strengths and limitations
Strengths of this study include the use of a RCT with a longitudinal design, that allowed us to follow-up a vulnerable population including pre- and post-COVID-19 measurements. Furthermore, the availability of quality data, especially device-based PA, which is rare in relatively large sample sizes and low-income settings like ours. However, our study also had some limitations. First, intervention schools participated in different conditions with three of four schools receiving external support, while intervention fidelity was not assessed. Nevertheless, the application of mixed linear models enabled us to account for the variability between schools, classes, and intervention delivery. Second, low accelerometer wear-times might lead to inaccurate results. We approach this limitation by only including valid and representative days and controlling for wear-time in the analyses. Third, choosing appropriate cardiovascular risk markers and defining accurate cut-off points in children is a topic of debate in the literature. Different markers exist for different outcomes, and some change with age and maturation state of the child. Thus, using the same cut-off point for all children might present an under- or overestimation of the actual risk. This is partially overcome by the use of age- and sex-adjusted percentiles for BMI and BP, while none are available for glucose or lipids. Finally, as our study focuses on health outcomes of especially vulnerable children, no long-term data from healthy children was available to compare the development of cardiometabolic markers over time.