Back to school after lockdown: The effect of COVID-19 restrictions on children's device-based physical activity metrics

Objective: The Coronavirus disease-2019 (COVID-19) pandemic and national lockdowns took away opportunities for children to be physically active. This study aimed to determine the effect of the COVID-19 lockdown on accelerometer-assessed physical activity (PA) in children in Wales. Methods: 800 participants (8 – 18-year-olds), stratified by sex, age and socio-economic status, wore Axivity AX3 accelerometers for seven days in February 2021 during the lockdown, and in May 2021 whilst in school. Raw accelerometer data were processed in R-package GGIR, and cut-point data, average acceleration (AvAcc), intensity gradient (IG) and MX metrics were extracted. Linear mixed models were used to assess the influence of time-point, sex, age and SES, on PA. Results: During lockdown, moderate-to-vigorous PA (MVPA) was 38.4 ± 24.3 min·day-1; sedentary time (ST) was 849.4 ± 196.6 min·day-1. PA levels increased significantly upon return to school (all variables p < 0.001). While there were no sex differences during lockdown (p = 0.233), girls engaged in significantly less MVPA than boys once back in school (p < 0.001). Furthermore, boys had more favourable intensity profiles than girls (IG: p < 0.001), regardless of time-point. PA levels decreased with age at both time-points; upper secondary school (USS) girls were the least active group, with an average M30 of 195.2 mg (whilst in school). Conclusion: The lockdown affected boys more than girls as reflected by the disappearance of the typical sex difference in PA levels during lockdown, although they were re-established on return to school. USS (especially girls) might need specific COVID-recovery intervention