Exploring the impact of revised physical activity guidelines on children and adolescents: an analysis of large Australian and New Zealand studies.

Objectives: Around 80% of children/adolescents globally do not meet recommended levels of physical activity (PA). The 2020 WHO consensus updated PA guidelines, changing from '60 minutes of PA/day' to at least 'an average of 60 min/day'. This means that attaining 420 min/week expresses the minimum threshold for PA.This analysis examined the effects of the changed guidelines on children/adolescents meeting PA guidelines. A coprimary research question examines single-item PA questions to determine the number of days of 60 min of activity that best reflect meeting the new PA guideline. Methods: Data were from five population-level Australian and New Zealand surveys (two representative population surveillance datasets and three large community interventions). PA questions included the single item question (days/week of 60 min) and detailed PA measures including International Physical Activity Questionnaire-adolescent questions. The single-item analysis used receiver operating characteristic (ROC) curves to identify the best fit between the single-item and more extensive PA measures (maximising sensitivity and specificity). Results: The proportion meeting the old PA guidelines ranged from 28-55%, compared with 35-84% meeting the new guideline (average absolute increase of 26.2%). ROC analysis described areas under the ROC curve between 0.728 and 0.907. The best fit (Youden's Index >0.5) was 4-5 days/week where the single item best classified children and adolescents meeting the new guideline. Conclusions: The new guideline classified 26% more children and adolescents meeting updated PA guidelines. National research reports should use updated PA guideline criteria, and for surveillance, 4-5 reported days/week on the single PA question best estimates meeting the PA guideline threshold.