One in four teenagers worldwide say they do not take part in regular physical activity

The study published in The Lancet Global Health by Strain and colleagues is of outstanding importance for the global monitoring of physical inactivity amongst adolescents. Its findings show that physical inactivity amongst adolescents has plateaued globally and that the gender gap remains particularly worrying: whilst boys report an average of three active days per week, girls barely reach 2.4 days, a difference that is observed across all regions.

Whilst, broadly speaking, the press release accurately reflects the study’s findings, it is important to interpret the headline’s data correctly. When the study states that one in four adolescents reports 0 active days per week, it does not scientifically imply that they are completely sedentary, but rather that they do not meet the authors’ recommended minimum of 60 minutes per day of moderate to vigorous physical activity. This figure is by no means arbitrary, but its origin warrants clarification: the World Health Organisation’s 2020 recommendations specify a required average of 60 minutes per day of moderate to vigorous physical activity per week. However, the study uses an epidemiological surveillance indicator based on the earlier 2010 recommendations, which counts the number of days on which at least 60 minutes of moderate or vigorous physical activity is achieved. This indicator allows for the analysis of historical trends, but is not directly equivalent to compliance with the current WHO recommendations, which are based on a weekly average. Furthermore, the data are collected via self-reported questionnaires which, whilst highly valid, are not equivalent to objective measurement using instruments (e.g. accelerometry).

The study is methodologically robust: it has a very large sample size and uses advanced statistical models that enable the generation of comparable estimates over time. Furthermore, it provides a very useful approach in terms of epidemiological surveillance, as it allows us to see how days of activity are distributed throughout the week, thereby enabling better-informed interventions tailored to different levels of activity. There are two points to note in terms of caveats: (1) the absence of data from India, which, given its population size (18 per cent of the world’s adolescent population), represents a significant limitation in the quantification of global estimates; and (2) the fact that the data were collected mainly in educational settings, which may exclude the non-school-attending population and thus obscure potential inequalities. Although the study identifies significant differences between countries and regions, the lack of analysis by individual or household socioeconomic status limits its ability to characterise social inequalities within each country. This is particularly relevant because differences between countries may mask significant internal social gradients, and because policies to promote physical activity should consider not only average activity levels but also how these are distributed across different socioeconomic groups.

The findings of the study by Strain et al. have particularly relevant implications for public health. The 15-year stagnation in adolescent physical activity levels highlights the need to rethink strategies for promoting physical activity, moving beyond interventions focused on individual behavioural changes and instead adopting population-level policies that alter the structures shaping the living conditions of the adolescent population. This requires a whole-of-system approach, involving education, urban planning, transport, sport and healthcare, to ensure that everyone has opportunities for accessible and sustainable physical activity in their daily lives. Within this framework, the gender gap emerges as a matter of immense significance in light of the data, requiring a gender-sensitive approach that tackles specific barriers such as stereotypes associated with participating in sport, perceptions of safety in sports facilities, and the unequal distribution of care responsibilities.

Finally, this research raises an important point: it is not enough to know whether we are increasing the average levels of physical activity amongst the population; we need to know who is benefiting from the policies implemented and who continues to be left behind. A public policy or intervention may succeed in increasing the average levels of physical activity amongst the population whilst, at the same time, reinforcing or even widening inequality. It is therefore important to conduct in-depth, disaggregated studies on inequality that inform equitable policies and prevent public efforts from being focused on improving the circumstances of those who already have greater opportunities.