text: Association of COVID 19 Mitigation Measures With Changes in Cardiorespiratory Fitness and Body Mass Index Among Children Aged 7 to 10 Years in Austria Previous studies have shown reductions in self reported physical activity levels in children associated with implementation of COVID 19 mitigation measures and data on objectively assessed health parameters are limited To examine the association of COVID 19 mitigation measures with changes in cardiorespiratory fitness CRF measures and body mass index BMI among primary schoolchildren This cohort study included children aged 7 to 10 years from 12 randomly selected primary schools in urban and rural districts of Klagenfurt Austria Baseline CRF and BMI measurements were obtained in September 2019 before COVID 19 mitigation measures were implemented and follow up measurements were obtained in June and September 2020 COVID 19 mitigation measures Cardiorespiratory fitness was measured with a 6 minute endurance run test Height and weight were objectively measured Standard deviation scores were calculated for CRF and BMI Changes over time were analyzed using analyses of variance Secondary analyses were performed for subgroups stratified by sex A total of 764 children 383 girls 50 1 aged 7 to 10 years had all measurements completed From September 2019 to September 2020 CRF SD scores changed by 1 06 95 CI 1 13 to 1 00 with a similar decrease in both boys and girls Body mass index SD scores had increased by 0 12 95 CI 0 06 0 16 in June 2020 and by 0 16 95 CI 0 12 0 20 in September 2020 compared with September 2019 The increase in BMI SD scores from September 2019 to September 2020 was greater among boys 0 23 95 CI 0 18 0 29 than among girls 0 09 95 CI 0 04 0 15 During the 1 year period the percentage of children with overweight or obesity increased from 20 3 155 children to 24 1 184 children difference 3 8 29 children In this cohort study of children in Austria COVID 19 mitigation measures were associated with decreases in CRF measures and increases in BMI The findings suggest that collaborative efforts are needed to reverse these changes in childrens health to prevent long term negative health outcomes 