key: cord-1042579-j2xnc2lc
authors: Hurter, Liezel; McNarry, Melitta; Stratton, Gareth; Mackintosh, Kelly
title: Back to school after lockdown: The effect of COVID-19 restrictions on children's device-based physical activity metrics
date: 2022-01-26
journal: J Sport Health Sci
DOI: 10.1016/j.jshs.2022.01.009
sha: 34470ce4d34ef0436ebc945f69b60521fbb15d26
doc_id: 1042579
cord_uid: j2xnc2lc

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 years old), stratified by sex, age, and socio-economic status, wore Axivity AX3 accelerometers for 7 days in February 2021, during the lockdown, and in May 2021, while 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; sedentary time was 849.4 ± 196.6 min/day. 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 favorable 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 (while 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 these were re-established on return to school. USS (especially girls) might need specific COVID-recovery intervention.

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 years old), stratified by sex, age, and socio-economic status, wore Axivity AX3 accelerometers for 7 days in February 2021, during the lockdown, and in May 2021, while 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; sedentary time was 849.4 ± 196.6 min/day. 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).

The coronavirus disease-2019 (COVID-19) has caused unprecedented disruption to the lifestyles of children and adolescents. Worldwide, governments imposed COVID-19 restrictions (lockdowns) on their citizens in an attempt to slow the spread of the virus. Wales, a devolved nation within the United Kingdom (UK), enforced several national lockdowns throughout the course of the pandemic. The closure of schools, sport clubs, and indoor fitness centers, including swimming pools, resulted in the removal of the primary sources of structure, routine, and physical activity (PA) for children and adolescents. Moreover, with lockdown rules prohibiting people from gathering, even in open spaces, all organized recreational activities ceased. Indeed, during the national lockdown, people in Wales were only allowed to leave their homes for essential reasons, which included food shopping, medical needs, traveling for essential work, and exercise, with senior government ministers and medics promoting 30 min of daily exercise.

Numerous studies have sought to document the effect of various COVID-19 restrictions on children's PA levels, with most studies included in recent systematic and scoping reviews 1, 2 reporting a decline in the PA levels of children and adolescents. Specifically, Medrano et al. 3 found that self-reported PA levels in 113 Spanish children (aged 8-16 years) declined by 91 min per day, while 36% of the parents of 211 children (aged 5-13 years) living in the United States reported their children had "done much less PA" compared with pre-pandemic levels. 4 Similarly, 31% of parents from a large-scale study (n = 16,177) in New South Wales, Australia reported that their children's PA levels had decreased "a lot" during COVID- 19. 5 However, to date, studies during the pandemic have relied on validated 3,6,7 or unvalidated online questionnaires. 8 Although self-and proxy-report measures enable large sample sizes and ease of administration while participants are confined to their homes, they are inherently associated with numerous disadvantages, including but not limited to recall errors (especially in children) 9 and social desirability. 10 It is therefore recommended that, ideally, such methods be used in combination with device-based measures, such as accelerometry. 11 No previous studies have quantified the change in accelerometer-derived PA in children and adolescents during and after COVID-19 lockdowns. However, it is imperative that devicebased data is not only used, but that the results are meaningful, interpretable, and comparable 12 in order to accurately inform strategies aiming to alleviate the impact of COVID-19. Over the last decade, significant advances have been made in accelerometer dataprocessing, with the field initially progressing from the traditionally used, device-specific, counts-based cut-point method, which was reliant on proprietary algorithms, to processing raw acceleration signals that enable inter-device and -study comparability. 13, 14 Raw acceleration signal processing allows researchers to report not only time spent in different intensities (using raw acceleration cut-points 15, 16 ), but also newly developed accelerometer metrics that, unlike cut-points, are not population-or protocol-specific. 12, 17, 18 The latter produce results that are easily comparable with maximal potential for data harmonization. 19 Therefore, the aim of this study was to determine the effects of the third national COVID-19 lockdown on a range of PA metrics using raw acceleration data in children and adolescents in Wales.

After gaining approval from Swansea University's Research Ethics Committee (reference number: KM_04-08-20b), 800 participants, stratified by sex, age, and socioeconomic status (SES), were randomly selected, from 1708 children and adolescents who completed an online survey and whose parents completed a parental consent form, to wear an Axivity AX3 triaxial accelerometer (Axivity Ltd, Newcastle, UK). The whole study took place remotely, with accelerometers and instructions mailed to participants. The first data collection time- while all children were back in school. Organized sport for children had resumed, and indoor swimming pools had reopened. Again, 800 Axivity monitors were mailed to participants. Of these, 734 had also participated during the lockdown time-point, while the rest were new recruits (66 participants from the first time-point either declined to wear a monitor for the second time-point, or their first device was not returned). Figure 1 shows the number of participants included in each phase of the study and analysis.

Accelerometers were initialized to start recording data 2 working days after postal dispatch, at a sampling frequency of 100 Hz. Participants were asked to start wearing the monitors immediately on receipt and to then wear the device continuously for 7 consecutive days on the non-dominant wrist. Devices were subsequently returned in a pre-paid envelope.

Accelerometer data were downloaded with OmGui open-source software (OmGui Version 1.0.0.43; Open Movement, Newcastle, UK), saved in .cwa format, and processed using Rpackage GGIR (Version 2.3-0; https://cran.r-project.org). 20 Signal processing in GGIR includes autocalibration using gravity as a reference 21 and the detection of non-wear.

Specifically, the default non-wear setting was used, whereby GGIR imputes non-wear data utilizing the average at similar time-points on other days of the week. GGIR also calculated the magnitude of dynamic acceleration corrected for gravity (Euclidean Norm minus 1 g, ENMO), averaged over 1-s epochs, and expressed in milli-gravitational units (mg). For their data to be included in the raw analysis, participants needed to log at least 16 h of wear-time per day. 13 GGIR was used to report raw acceleration cut-point data, including sedentary time (ST; defined as waking time accumulated below the 50 mg threshold), 15 light PA (LPA), and moderate-to-vigorous intensity PA (MVPA; defined as time accumulated above 191.6 mg), 22 all obtained from GGIR output Part 5. While these cut-points were developed using GENEActiv devices, the GENEActiv and Axivity accelerometers have shown excellent equivalence and agreement across most raw data outcome measures. 13, 23 Furthermore, AvAcc (mg), intensity gradient (IG), and the acceleration above which a person's most active 180, 60, 45, 30, 15, and 5 min were accumulated (MX metrics; mg), are reported from GGIR output Part 2. The AvAcc is a direct measure of dynamic acceleration and is used as a single metric for the overall activity averaged per day. 19 The IG reflects the distribution of acceleration intensity across the 24-h day by plotting the natural logs of time accumulated against acceleration intensity, resulting in a straight-line (negative slope) graph. A steeper, more negative gradient reflects a poorer intensity profile, with the person spending more time in the low-to mid-range intensities, whereas a shallow, less negative (higher) gradient means more time was spent in higher intensities, thus reflecting a more favorable intensity profile. 17 The MX metrics allow for post hoc translation of accelerometer metrics, meaning that researchers can apply any cut-point or acceleration associated with a specific activity to the dataset. 24 The latter facilitates easily interpretable public health messages. For example, acceleration intensities ranging from 100-200 mg are indicative of a slow walk; >200-350 mg, a brisk walk; >350-500 mg, fast walking or jogging; while >500-1000 mg indicates slow running; >1000-1500 mg, medium running; >1500-2000 mg, fast running, and >2000 mg, sprinting or jumping. 25 Descriptive statistics (means ± SD) by age group, sex, and SES were calculated for all variables. Participants were divided into 3 age groups, according to school year: (a) Years 4-6 (n = 300; girls = 150; 9.9 ± 0.9 years), called "upper primary school" (UPS); (b) Years 7-9 (n = 292; girls = 149; 12.9 ± 0.9 years), called "lower secondary school" (LSS); and (c) Years 10-13 (n = 208; girls = 115; 15.6 ± 0.9 years), called "upper secondary school" (USS). To gain a measure of SES, the Welsh Index of Multiple Deprivation 26 was used to divide participants into quintiles. Quintiles were ranked from 1 to 5, representing the most-and least-deprived group, respectively.

Linear mixed models were conducted separately for each PA metric to investigate the differences between lockdown and school data and to assess the influence of time-point, sex, age group, and SES, along with their interaction, on PA metrics, with planned contrasts used to further explore significant interaction effects. Results are reported as beta coefficients (β), 95% confidence intervals (95%CI) or standard error (SE), and p values, with level of significance set as p < 0.05. Sensitivity analyses were run by repeating the same analyses 3 times but varying the inclusion criteria from at least three valid days to 2 and, finally, at least one valid day. Statistical significance remained the same after relaxing the inclusion criteria; therefore, it was decided to use at least one valid day's data, in order to include more participants, thus adding power to the analyses and reducing bias. 27 Analysis was conducted in STATA MP (Version 13, Statacorp., College Station, TX, USA).

All PA variables increased significantly once children returned to school after lockdown (all p < 0.001; Table 1 and Supplementary Table 1 Differences between age groups across time-points for both sexes are further illustrated with radar plots (Fig. 2) and Supplementary Table 3 . Across the intensity spectrum, UPS children, irrespective of sex or time-point, had consistently higher values than those in LSS and USS.

For boys during lockdown, the biggest drop in MX values across the spectrum occurred between UPS and LSS ( Fig. 2A) . Upon return to school, MX values for both UPS and LSS increased, as is particularly evident in the greater surface areas covered around the lower MX variables (Fig. 2B) . The decrease in MX values for girls in lockdown from UPS to LSS continues noticeably to USS (Fig. 2C) , while as with boys, girls in USS barely showed a difference across time-points (Fig. 2D) 

The aim of this study was to determine the effect of the COVID-19 lockdown on the PA levels and intensities of children and adolescents using various accelerometer metrics.

Overall, PA levels increased significantly upon return to school, with widening differences between girls and boys and a significant decline in PA with age.

The PA levels during lockdown were low in comparison to values reported pre-COVID-19. 29 These findings are not surprising given that COVID-19 restrictions removed many opportunities for children and adolescents to be active, such as sport clubs, active travel to school, and school break times. It is also pertinent to note that the results are in accord with self-reported levels during lockdown periods. 1 However, the extent of the effect of lockdown on the PA levels of children and adolescents was, perhaps, greater than expected. While it could be postulated that the low PA levels are a result of the cut-points utilized being developed in 7 to 11-year-olds 22 and 9 to 10-year-olds, 15 and so therefore not encompassing the full age range of the present sample, this is unlikely given that the MX metrics were congruent across all age groups. During lockdown, children and adolescents did not reach intensities indicative of a brisk walk (200 mg) for 45 min/day. 25 Contrary to research conducted pre-COVID-19, 30, 31 there were no significant sex differences in MVPA according to applied cut-points. Previous research has shown that extracurricular sport participation is higher in boys than in girls, 32 which might explain this finding as lockdown rules prohibited all organized sport participation. Elnaggar et al. 33 also reported a more prominent drop in the PA levels of boys as compared to girls during social distancing measures while organized sport was banned. However, IG results revealed that boys still had more favorable intensity profiles, which are associated with health indicators such as obesity, metabolic risk, and cardiorespiratory fitness. 14 The higher IG found in boys during lockdown was driven by the low duration MX metrics, with boys achieving significantly higher intensities during their most active 15 and 5 min of the day compared to girls. Of interest, the previously reported sex differences in MVPA 30 were re-established upon return to school, suggesting that the sociocultural environment at school may be more conducive for boys to be physically active than for girls. Of particular concern are the PA levels and intensities of However, the larger increase in all PA variables upon returning to school for UPS children suggests that younger children were more affected by the COVID-19 restrictions than older children. This is perhaps expected given that younger children are less likely to go out independently; thus, they rely on parents or care-takers to accompany them 34 and/or utilize school break times to be more active. 35 This study has several strengths. It is the first study to utilize device-based PA assessment in children and adolescents during a COVID-19 lockdown. Furthermore, repeating data collection at a second time-point enabled intra-participant comparisons across different stages of the COVID-19 pandemic, which, combined with the use of various accelerometer metrics, resulted in new insights into the differences of PA between boys and girls. The wide age range of participants included in the study facilitated primary and secondary school comparisons, in which there were stark differences. The sample size was large and countryspecific, with participants stratified by age, sex, and SES, and thus provided a dataset demographically representative of children and adolescents in Wales. Nonetheless, the study is not without limitations. Indeed, the initial lockdown period took place in winter, which has been shown to be associated with lower PA levels in youth populations. 36 Given that USS adolescents, particularly girls, demonstrated such undesirable PA profiles upon return to school, despite the lifting of COVID-19 restrictions and data being collected in springtime, the importance of this finding cannot be overstated. Furthermore, the use of accelerometry to examine movement behaviors in isolation, without any contextual information, limits the conclusions that can be drawn.

Using a range of accelerometer metrics, this study provides results quantifying the effect that the COVID-19 lockdown has had on PA in children and adolescents. PA levels in boys were more negatively affected by the lockdown than those of girls, though there were significant differences in the PA profiles, irrespective of sex, during both time-points. While PA levels of UPS children and younger boys increased immediately upon return to school, similar COVID-recovery behavior was not evident in USS. Given the low, and indeed decreased, levels of PA in USS pupils (especially girls), future interventions should seek to specifically target this age group.

KM conceived and designed the study, assisted with data collection, and provided critical feedback on the manuscript; MM conceived and designed the study, assisted with data collection, conducted the statistical analysis, and provided critical feedback on the manuscript; GS conceived and designed the study and provided critical feedback on the manuscript; LH collected, processed, and analyzed the data, and wrote the first draft. All authors read and approved the final draft of the manuscript, and agree with the order of presentation of the authors. 

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Table 1: Change in all variables between lockdown and return to school from participants with data at both timepoints (means ± SD)

The authors would like to thank all the children who took part in this study as well as their parents, who provided consent. This research was funded by the Welsh Government Sêr 

The authors declare that they have no competing interests.