The aim of this portion of a larger systematic review was to evaluate the effects of interventions on children’s and adolescents’ overall PA in both boys and girls, and to appraise the extent to which the studies have taken sex/gender into account. This review included 94 studies with 164 PA outcomes included measuring a wide range of PA outcomes by any type of measure (subjective/objective). Our review shows that in most PA outcomes the same or similar intervention effects were observed for boys and girls (105 out 120 PA outcomes). The quality of reporting sex/gender aspects captured by applying the newly developed sex/gender checklist was low.
Overall PA is too low in many children and adolescents (6) and thus, improving overall PA is an important concern for both boys and girls. However, as overall PA levels are especially low in girls (35), interventions should contribute to the reduction, or at least not increase, the gradient of sex/gender inequalities in overall PA in childhood and adolescence. In summary, the review revealed that only one third of the outcomes showed improvements in overall PA leading to the conclusion that most interventions failed to increase overall PA. However, this review also identified that most successful interventions were effective for both boys and girls. Furthermore, studies reporting the same or similar effects of PA interventions in boys and girls were more often rated as ‘detailed’ with regard to sex/gender consideration across all items of the checklist when compared with studies reporting different effects. This might suggest that considering sex/gender during intervention planning, development, delivery and analyses increased the likelihood of impact for all. In particular, the items measurement instruments, participant flow, and intervention content and materials were taken into account more strongly in interventions with outcomes with equal effectiveness.
The application of measurement instruments that are sex/gender invariant is important. For example, it has been reported that the Yamax pedometer underestimated the number of steps at slower walking speed. Consequently, lower step counts of girls could be a result of underestimation because girls tend to have smaller stride length, resulting in slower walking speeds (36). To minimize bias arising from measurement used, it is necessary to consider sex/gender specific characteristics (e.g., weight, height or BMI). Sigmund et al. (33) used relative energy expenditure values for group comparison of boys and girls with different body weights, a measure without apparent gender bias, and found similar intervention effects for boys and girls.
Conclusions about effectiveness should make allowance for participant flow. For conducting sex/gender-based analyses it is important to take into account and to report on the flow of participants according to sex/gender (e.g., recruited, enrolled, completed). This has not been done in eighty percent of the included studies as the ratings of our sex/gender checklist revealed. For example, dropout rates (as one indicator of participant flow) from sports participation have been shown to be higher in girls compared to boys. Therefore, sex/gender distribution might be equal for recruitment but not for post or follow-up measurement (37). As a best practice example out of the included studies in this review, Beets et al. (38) presented the number of participants for baseline, post-intervention and follow-up disaggregated with regard to sex/gender.
Additionally, intervention content and materials should be gender-sensitive to address all participants. As an example, Pardo et al. (39) stated that their intervention program attempted to address the specific interests and needs of boys and girls (e.g., by encouraging them to express their opinions and offer suggestions during the tutorial session), while offering an overall program strategy that was similar for boys and girls. Such considerations may enhance the applicability of interventions for all groups regardless of sex/gender.
For single sex/gender studies, only 23% of PA outcomes showed significant intervention effects (14.3% of PA outcomes for boys and 24.3% of PA outcomes for girls). Interventions with PA outcomes without a significant intervention effect were more often rated as ‘detailed’ with regard to sex/gender consideration. This finding is surprising as interventions in which sex/gender was considered more strongly might be anticipated to be more effective. It is possible that ineffective interventions were reported more precisely with regard to sex/gender consideration than effective ones to overcome potential criticism on the concept and conduct of ineffective interventions (40, 41). Additionally, the ineffectiveness of most single sex/gender studies could be explained by considering previous research indicating that girls and boys tended to accrue more moderate-to-vigorous PA (MVPA) in coeducational than in unisex classes (42, 43). Average percentages of physical education time spent in MVPA in coeducational classes is higher than those recorded in unisex classes (43). Girls and boys reported that they have more fun and a higher social motivation in coeducational classes compared to unisex classes (44). Nevertheless, as shown in another review on equity effects of children's physical activity interventions (23), there is no clear evidence on comparative effectiveness of targeted interventions focussing on a specific high-risk subgroup (like girls) and universally targeted interventions. Thus, further research is needed to understand if targeted (intervention with tailored intervention content) or non-targeted interventions are more effective (23) and whether single sex/gender interventions can be effective.
Implications for research and practice
There is a need to address the inconsistent use of terms sex and gender, the insufficient consideration of sex/gender in developing and implementing interventions, and the lack of robust sex/gender analysis in PA intervention studies. This review demonstrates a need for continued efforts to improve appropriate consideration and reporting of sex/gender during all steps of intervention planning, development, delivery and analysis. Although a variety of initiatives (e.g., Canadian Institutes of Health Research, the Gender Policy Committee of European Association of Science Editors) have attempted to increase the degree to which sex/gender is considered in studies, no appropriate guidelines encompassing sex/gender in interventions and systematic reviews in the context of overall PA exist (45-47). It is important to consider sex/gender aspects to reduce any sex/gender gap in terms of overall PA. The newly developed sex/gender checklist can help researchers by applying the sex/gender items of the checklist during the development, implementation, and appraisal of overall PA promotion programs. For further research, we recommend identifying and analysing potential moderators such as age, different intervention contents, settings, or methods, different types of overall PA outcomes, cultural or regional location etc. that could have an impact on the effects of the interventions. Finally, to assess the strength of a body of evidence and to carry out the relationship between the results of interventions and the risk of bias, it is advisable for further studies to consider risk of bias in the data synthesis approach (e.g., conduct sensitive analysis and exclude high risk of bias studies from the analysis).
Strengths and limitations
To our best knowledge our systematic review and semi-quantitative analysis is the first to systematically assess how sex/gender aspects are considered in interventions promoting overall PA in children and/or adolescents. No previous review appraised the extent to which the studies have taken sex/gender into account with a comprehensive checklist and systematically analysed the effectiveness with regard to sex/gender. Furthermore, through our inclusive approach to PA promotion activities, which was not limited to only behavioural and cognitive strategies, we were able to highlight a range of different programmes to improve overall PA in children and/or adolescents. Another strength of the systematic review was using the PRISMA statement to improve the reporting quality.
However, this work has also some limitations. The review is limited to English language articles and did not include studies published in other languages. Furthermore, the research was limited to peer-reviewed journal articles and thus, results of other intervention studies published in other types of literatures were excluded. Regarding the considerations of sex/gender aspects in the primary studies, we were not able to differentiate if these aspects were neglected or just fragmentary or insufficiently reported. However, this can lead to bias and undervaluation of sex/gender considerations in primary studies. It is also worth mentioning, that conclusions should be interpreted carefully because of inability to conduct a meta-analysis because of the heterogeneity of studies. We conducted semi-quantitative analyses using the ratings of the sex/gender checklist without taking their relative weight into account, because until now no theoretical assumption about the weight of the items exists. Additionally, based on the available primary data we were not able to determine if the interventions contributed to gender equity. We just analysed if boys and girls benefited similarly from the intervention regardless of their starting levels of overall PA. Thus, even if they benefited equally at the end of the intervention there can still be unequal levels of overall PA. Finally, our work here is also limited to focusing on the binary characterisation of gender (boys and girls) because none of the included studies included gender diverse participants.