Declines in Physical Activity and Cardiorespiratory Fitness After Implementing new National School Guidelines.

PURPOSE:We examined whether introduction of national guidelines limiting sports club activities at school was associated with adolescents' exercise and cardiorespiratory fitness. METHODS:We conducted interrupted time-series analysis to quantify the changes in prefecture-level aggregated data on exercise or sports activities and 20-m shuttle run (indicator of cardiorespiratory fitness) among adolescents in Japan before (2013-2017) and after (2018-2022) the introduction of the guidelines using data from the National Survey of Physical Fitness, Athletic Performance and Exercise Habits. RESULTS:The introduction of the guidelines was associated with reductions in exercise and sports activities duration (boys, -4.8 [95% CI -5.9, -3.8] min/day; girls, -5.5 [95% CI -6.2, -4.8] min/day) and performance of 20-m shuttle run (boys, -1.2 [95% CI -1.4, -1.0] laps; girls, -2.3 [95% CI -2.5, -2.2] laps). DISCUSSION:After introducing guidelines limiting sports club activities at school, levels of exercise or sports and cardiorespiratory fitness declined among adolescents.