[How comparable are physical activity data? Methodological differences and their implications for evidence-based policy decisions].

Physical activity is a key determinant of health and plays a crucial role in the prevention of various chronic diseases and mental disorders. Numerous studies demonstrate the positive effects of regular physical activity on morbidity, mortality, and quality of life. Recent global analyses, such as the Lancet study by Strain et al. (2024), indicate comparatively high compliance with WHO physical activity recommendations in Germany and estimate the proportion of insufficiently active adults at around 12%. In contrast, national surveys report substantially higher rates of up to 54%.This discussion article takes this discrepancy as a starting point to compare and methodologically contextualize study findings. Differences in measurement instruments, survey modes, domains considered, operational definitions, and modelling approaches can substantially influence prevalence estimates and limit comparability across studies. Self-reported data may overestimate physical activity, while objective measures such as accelerometry present their own methodological challenges.Internationally modeled estimates provide valuable data for cross-country comparisons but should be interpreted in light of their methodological foundations when assessing the national situation. Further methodological development is needed in assessing physical activity. Combining self-report and objective measurement could help provide a more robust basis for evidence-based policy decisions to promote physical activity.