key: cord-0972340-n06nmz4o
authors: Kharel, Madhu; Sakamoto, Jennifer Lisa; Carandang, Rogie Royce; Ulambayar, Shinejil; Shibanuma, Akira; Yarotskaya, Ekaterina; Basargina, Milana; Jimba, Masamine
title: Impact of COVID-19 pandemic lockdown on movement behaviours of children and adolescents: a systematic review
date: 2022-01-25
journal: BMJ Glob Health
DOI: 10.1136/bmjgh-2021-007190
sha: cd14f4d4ead976b6240df26dafff4cc30f838e82
doc_id: 972340
cord_uid: n06nmz4o

INTRODUCTION: Several studies have examined how the lockdown restrictions enforced to halt the spread of COVID-19 have affected children and adolescents’ movement behaviours, but there is a need to synthesise these findings. Therefore, we conducted this systematic review to examine the impact of COVID-19 lockdown on children and adolescents’ movement behaviours. METHODS: We searched eight databases and grey literature for relevant studies of all study designs; and conducted a narrative analysis of the results following synthesis without meta-analysis guidelines. We used appropriate tools to assess the risk of bias in quantitative and qualitative studies. We compared changes in physical activity, screen time and sleep duration and quality from before to during the COVID-19 lockdown. RESULTS: This review included 71 studies reporting data from 35 countries and territories, mostly from high-income economies. A majority of the studies used a cross-sectional design and had fair to poor-quality ratings. Most studies reported reduced physical activity, increased screen time and longer sleep hours among children and adolescents. Children and adolescents facing strict lockdowns saw a larger decline in physical activity and a sharper increase in screen time than those under mild restrictions. CONCLUSION: COVID-19-related lockdowns were detrimental to children and adolescents’ movement behaviours, with stricter lockdowns tending to have a bigger impact. Children and adolescents under COVID-19 restrictions are likely to be less active, spend more time on screen, and sleep longer hours than before the lockdown. More studies from low-income and middle-income countries could provide a clearer picture of the impact. PROSPERO REGISTRATION NUMBER: CRD42021245924.

COVID-19, one of the biggest pandemics in the history of humankind, has affected almost every country worldwide. The COVID-19 outbreak that started in Wuhan, China, in December 2019 has caused 317.26 million infections and 5.52 million deaths globally as of 13 January 2022. 1 WHO declared a Public Health Emergency of International Concern on 30 January 2020 to accelerate action against the rapidly spreading coronavirus. 2 Following the WHO recommendations, governments in many countries started to enforce lockdown measures to curb the spread of the virus. During these lockdowns, schools, businesses and other non-essential services were closed, and people were advised to stay inside their What are the new findings?

► Lockdown measures to contain the spread of COVID-19 had mostly negative consequences on the movement behaviours of children and adolescents worldwide, with children spending less time on physical activity and more time on screens during confinement than before the pandemic. ► Children and adolescents facing milder restrictions, such that they were allowed to go outdoors for exercise while maintaining social distance, were physically more active and used screens less than those under stricter lockdowns. ► Children and adolescents had later bedtime and wake-up time during the pandemic than before the pandemic.

What do the new findings imply?

► When implementing measures to contain the spread of infections, authorities should carefully consider the negative consequences of the measures on the healthy movement behaviours of children and adolescents. ► Such measures should be introduced in a way that would have the least effect on children and adolescents' healthy movement behaviours.

homes. In extreme cases, public parks were also closed, and people were not allowed to go out, except for emergencies. 3 Lockdown restrictions greatly affected people's lives, especially those of children and adolescents. 4 Schools, where children and adolescents spend a significant amount of time, were closed for months. Their daily routines changed drastically, and they had more free time. However, as they had limited opportunity to go outdoors due to lockdown restrictions and fear of contracting the virus while being outdoors, 5 they had to spend most of their time inside their residence. Such confinement of children and adolescents inside their house during this active age can negatively affect their movement behaviours-physical activity, sedentary behaviour and sleep. 6 Healthy movement behaviours-adequate physical activity, limited sedentary behaviour, and sufficient sleep-are critical for healthy childhood development. 7 However, these behaviours might be compromised during lockdown restrictions. School closure means children cannot participate in physical education classes, which are a significant contributor to children's total physical activity under normal circumstances. 8 School closure also affects active commute to and from the school. 9 Additionally, having limited opportunities to go outdoors during the lockdown would significantly reduce children's outdoor play. Confined children with more free time might turn to screen-based electronic devices such as mobile phones, tablets, computers and television for leisure activities. 10 Children's sleep patterns might become irregular as they do not have to attend regular classes. 11 12 Their sleep quality might decrease during the lockdown because of the fear and anxiety caused by the pandemic. [13] [14] [15] Unhealthy movement behaviours are associated with adverse health outcomes such as obesity, hypertension, diabetes, cardiovascular diseases, poor mental health and lower health-related quality of life. [16] [17] [18] Several individual studies have been conducted in various countries to see the impact of COVID-19-related lockdown restrictions on children and adolescents' movement behaviours. However, the results reported by these studies vary in both the degree and the direction of effect. 3 19 20 Moreover, the degree of lockdown restrictions varies between and within countries and can affect children and adolescents' movement behaviours differently. Stockwell and colleagues conducted a systematic review to examine changes in physical activity and sedentary behaviour from before to during COVID-19 lockdown among the general population. 21 However, this review included few studies on children and adolescents as it included studies until October 2020. A systematic review and meta-analysis was conducted to assess the prevalence and pattern of sleep disturbances in children and adolescents during the COVID-19 pandemic. However, this review searched articles only in three databases, and therefore, included few studies. 22 A narrative review of the literature was done to understand health-related behaviours among isolated preschool and school-aged children aged 3-12. 23 This narrative review included articles from a limited number of databases, focused on children in social isolation and social deprivation, and excluded children with previous health conditions or diseases. Similarly, Paterson et al conducted a scoping review to explore the impact of COVID-19 on the movement behaviours of children and youth aged 5-17 years. However, this review did not appraise the quality of the evidence, included some articles without peer review, and did not account for the varying degrees of lockdown restrictions. 24 Moreover, many studies have been published on this topic since these reviews were undertaken. Therefore, we conducted this systematic review to comprehensively review the findings from studies conducted in different settings and varying degrees of lockdown restrictions to inform policy decisions on enforcement of lockdowns for subsequent waves of COVID-19 and future pandemics of similar nature.

We registered the review protocol in PROSPERO (registration number: CRD42021245924, see online supplemental file 1) and followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines and synthesis without meta-analysis (SWiM) guidelines. 25 

We defined the population, exposure, comparators, outcomes and studies for this review as follows:

Population: Children and adolescents (aged 19 years and below) Exposure: COVID-19 pandemic lockdown We took the reference of an earlier study 26 and used the information provided in each article to categorise the severity of lockdown into the following five categories. 1. Mild lockdown: schools open, advised to maintain social distance. 2. Moderate lockdown: schools closed or available to children of essential workers, advised to stay indoors and maintain social distance while being outdoors. 3. Strict lockdown: schools closed, non-essential businesses closed, mandatory home confinement except for essential reasons, ban on public gatherings, closure of organised sports and recreation facilities, public parks open, allowed to go outdoors at least for a certain time. 4. Very strict lockdown: schools closed, non-essential businesses closed, closure of organised sports and recreation facilities, closure of public parks, not allowed to go outdoors even for exercise. 5 . Unclear: no sufficient information on lockdown available. Comparators: Outcomes before the COVID-19 lockdown versus outcomes during the COVID-19 lockdown.

Outcomes: Movement behaviours-physical activity, sedentary behaviours and sleep. 27 To be more specific, physical activity is defined as any bodily movement produced by skeletal muscles that requires energy expenditure. 28 It can take different forms such as walking, cycling, sports, active recreation and play, and household chores. 28 29 Based on intensity, physical activity can be categorised into light, moderate and vigorous. 30 Sedentary behaviour is any waking behaviour characterised by an energy expenditure ≤1.5 metabolic equivalents, while in sitting, reclining or lying posture. 31 Sedentary behaviours include sitting and using screens, such as watching television and using smartphones and computers for playing videogames and accessing the internet and social media. 31 In this review, sedentary behaviour included use of screens.

Sleep duration is the period between bedtime and wake-up time. 32 Sleep quality refers to how well one sleeps, and can be determined by various components, such as sleep duration, sleep disturbance, sleep latency and sleep efficiency. 33 34 Types of studies: We included original research articles with all types of study designs, such as randomised controlled trial (RCT), quasi-experimental, cohort, observational, cross-sectional and other comparative studies, as well as case studies and evaluation reports. We excluded letters, editorials, reviews, conference abstracts and books. Our search strategy combined both Medical Subject Headings (MeSH) terms and free-text terms related to children/adolescents AND lockdown AND movement and play behaviours (see online supplemental file 2).

Authors RRC and JLS independently searched the aforementioned electronic databases using the search strategy outlined in the review protocol. The titles and abstracts of all the articles retrieved from the search were screened by the two researchers independently, and duplicates were removed. The full texts of the potential articles to be included in the study were then reviewed by two researchers (MK and SU) independently based on the inclusion criteria. Any discrepancies between the two researchers were resolved through discussion with a third researcher (RRC).

We extracted data from the selected studies using an excel sheet, and included the following information: author, year and country; study title; source; study design; study setting; study population; sample size; mean age; proportion of female; measurement tools for physical activity, sedentary behaviour and sleep; description of lockdown; comparison; outcomes and remarks.

All the studies finally included in this review were observational. We used the 'Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies' of the US Department of Health and Human Services, National Institutes of Health to assess the risk of bias for cohort and cross-sectional studies. 35 For qualitative studies, we used the 'Qualitative study: Critical Appraisal Skills Programme'. 36 None of the included studies used RCTs or mixed-methods design. We used an approach reported by Geere et al to rate the strength of evidence from observational cohort and cross-sectional studies, considering study quality, number of evidence and consistency of findings. 37 

We did not perform a meta-analysis due to the heterogeneity of designs and measures in the included studies. Therefore, we conducted a narrative analysis of the results following the SWiM guidelines (see online supplemental file 3). 38 We categorised studies according to the three outcomes-physical activity, sedentary behaviour (screen time) and sleep (duration and quality), and described changes in relevant indicators from before to during the COVID-19 lockdown (see figure 1). Studies under each outcome were presented based on the direction (ie, increased, decreased, no significant change from before to during the lockdown) and the effect size of their results. When necessary, we standardised the unit of outcome measurements reported among included studies to compare the results easily. Figure 2 shows the PRISMA flow diagram. Initially, we retrieved 14 241 records from the database search and identified an additional 16 articles from other sources. After removing the duplicates and screening the titles and abstracts of the articles, the full texts of 150 potential articles were assessed. Finally, we included 71 articles after removing ineligible articles (see online supplemental table 1) .

Studies included in this review came from a range of countries and territories-11 studies reported data from Italy; 9 from the USA; 7 each from Spain and Turkey; 6 from Australia; 5 each from Canada and China; 4 each from the UK, Poland and India; 3 each from France and Portugal; 2 each from Germany, the Netherlands, Switzerland, Brazil, Chile, Hong Kong (China) and Malaysia; and 1 each from Croatia, Ireland, Russia, Sweden, Ukraine, Bangladesh, Indonesia, Israel, Pakistan, Singapore, Sri Lanka, Uzbekistan, Vietnam, Colombia, Egypt and Morocco. Of the 71 studies included in this review, 67 were single-country studies-the majority (51) from high-income economies, 13 from upper-middle-income economies and 3 from lower-middle-income economies; and 4 were multicountry studies reporting data from high-income, upper-middle-income and lower-middleincome economies. However, one of the multicountry studies did not specify the countries, instead reported that data were collected mostly from North America, the Middle East, Europe and South America. There were no studies from low-income countries. Twenty-three and 48 studies were published in 2020 and 2021, respectively.

Characteristics of studies included in this review are presented in table 1. All the studies were observational, and the majority were quantitative studies. Of the 71 studies, 20 were cohort (data were collected at two time points, for before lockdown and during the lockdown; prospective=18 and retrospective=2), 48 were cross-sectional (data were collected at the same time, for during lockdown and retrospectively for before the lockdown or repeated cross-sectional), and 3 were qualitative in design. The sample size (range: 9-29 202) and participants' age (range: 1-19 years) among the included studies varied widely. A majority of the studies (69%,) reported strict lockdown, while 9.8% reported moderate lockdown, 8.5% reported very strict lockdown, 4.2% reported mild lockdown and 8.5% did not provide sufficient information on lockdown.

The risk of bias assessment for the included quantitative studies is presented in online supplemental table 2. Almost all the studies clearly stated their research objective, defined their study population and recruited the study population following the inclusion and exclusion criteria. However, most studies (86.8%) did not justify the sample size as they used a convenience sampling strategy. None of the studies measured exposure prior to the outcome because most of them used a cross-sectional study design. More than 86% of the studies did not have significant issues in measuring exposure and outcome. Only 36.8% of the studies had adjusted for potential confounders. The quality appraisal of qualitative studies is presented in online supplemental table 3. All the three studies did not have any major issues in their design and implementation.

Physical activity Changes in physical activity from before to during the lockdown are presented in table 2. Thirty-four studies (11 cohort, 21 cross-sectional and 2 qualitative) reported changes in physical activity among apparently healthy children and adolescents from before to during the lockdown. Of these, 25 studies (8 cohort and 16 crosssectional and 1 qualitative) 3 27 39-61 observed a decline in physical activity, 8 (2 cohort, 5 cross-sectional and 1 qualitative) 9 20 26 62-66 observed no change and 1 (cohort) 19 reported an increase in physical activity.

The decline in physical activity among children and adolescents during the lockdown ranged from 102.5 min per week in a study in Spain 3 to 91 min per day in another study from the same country. 52 In Brazil, 83% of the adolescents spent less or much less time on physical activity during the pandemic than before the pandemic, 58 and the proportion of physically active children reduced from 59.1% to 7.0% during the same period. 57 Reductions in physical activity levels were also observed among children and adolescents in Chile, Singapore, the UK, Croatia, Australia (New South Wales), Canada, Poland, the USA, China, France, Portugal, Italy and Turkey. 27 39 41-51 53 55 56 59-61 In contrast, in some countries, children and adolescents could maintain or even increase their physical activity levels despite the pandemic restrictions. For example, studies from Italy, China, Australia (Western Australia) and Poland observed no significant change in physical activity levels from before to during the lockdown among children and adolescents. 20 63 65 66 A multicountry longitudinal study also reported no significant change in time spent on total physical activity among children aged 3-5 years old. 26 German children and adolescents were found 

to be more active during the COVID-19 lockdown, as the number of days active in a week and the proportion adhering to physical activity guidelines increased during this period (4.3 days/week to 4.7 days/week, p<0.01; and 19.1% to 30.2%, p<0.01; respectively). 19 Sedentary behaviour Exposure to screen Changes in screen time from before to during the lockdown are presented in table 3. Thirty-one studies (8 cohort, 21 cross-sectional and 2 qualitative) compared children and adolescents' screen time before and during the lockdown. All of them observed an increase in screen time during the pandemic compared with before the pandemic. During the lockdown, the increase in children's screen time ranged from 55 min per day in a multicountry study 26 to 2.9 hours per day in Spain. 3 Another study from Spain found that children's screen time increased by 1.8 hours per day, reaching an alarming figure of 6.1 hours per day during the lockdown. 52 Singaporean and German children spent daily 1.54 hours and 1.02 hours more, respectively, on screen during the pandemic than before the pandemic. 19 50 In Italy, 9 out of 10 Italian children spent more time on screen during the lockdown than before the lockdown 44 and the proportion of children and adolescents using smartphone for four or more hours per day increased from 16.3% before the lockdown to 66.3% during the lockdown. 67 In Brazil, nearly three-fourths of the children reported spending more or much more time on screen during the lockdown than before the pandemic. 58 Similar findings were reported in studies from Canada, China, Turkey and Portugal. 49 53 56 68 Approximately two-thirds of the children and adolescents in France and India spent more time on screen during the lockdown than before the lockdown. 46 69 Sleep Sleep duration, bedtime and wake-up time Changes in sleep duration, bedtime and wake-up time from before to during the lockdown are presented in table 4. Twenty-five studies (9 cohort and 16 crosssectional) reported changes in sleep duration among children and adolescents from before to during the pandemic. Twelve studies (five cohort and seven crosssectional) 27 75 76 reported no significant change in sleep duration. The increase in daily sleep duration among children and adolescents ranged from 11 min in Chile and the USA to approximately 1 hour in a multicountry study. 39 70 72 Spanish children slept approximately 48 min more on weekdays and approximately 42 min more on weekends during the COVID-19 confinement. 52 Similar results were observed among preschoolers in China. 74 Italian and Singaporean children slept approximately 27 min and 20 min more, respectively, during the lockdown than before the lockdown. 50 71 Studies from the UK and Poland reported that children slept less during the lockdown than before the lockdown. 51 54 Two multicountry studies and studies from Spain, Australia, the USA, Portugal and China did not observe any significant difference in sleep duration among children and adolescents from before to during the lockdown. 3 20 26 40 49 55 56 75 76 Ten studies 26 50 61 71 73-75 77-79 compared bedtime and wake-up time and one more study 72 compared wake-up time before and during the lockdown. All of them reported that children and adolescents went to bed later and woke up later during the COVID-19 lockdown than before the lockdown, except three studies, of which one 61 reported no change in wake-up time and two 77 79 reported no change in wake-up time on weekend days from before to during the lockdown. In Italy, children's bedtime and wake-up time shifted by 53 min and 66 min, respectively. 78 A similar shift in bedtime and wake-up time was observed among Singaporean children. 50 A multicountry longitudinal study among children aged 3-5 years observed that children went to bed 34 min later and woke up 59 min later. 26 

Changes in sleep quality from before to during the lockdown are presented in table 4. Nineteen studies (4 cohort, 14 cross-sectional and 1 qualitative) reported changes in sleep quality from before to during the COVID-19 lockdown. Eight (one cohort, six cross-sectional and one qualitative) 39 40 47 71 80-83 of them observed a decrease, five (one cohort and four cross-sectional) 27 51 73 74 79 observed an increase and six (two cohort and four crosssectional) 26 53 76-78 84 observed no significant change in sleep quality.

A decline in sleep quality was reported in studies from Chile, Spain, Turkey, Egypt, Italy, the UK and the Netherlands. 39 40 47 71 80-83 In Chile, sleep quality among toddlers and preschoolers declined during the COVID-19 pandemic (sleep quality mean score: 5.68 before the pandemic vs 4.93 during the pandemic, p<0.001). 39 Spanish preschoolers showed decreased sleep efficiency during the lockdown (84.3% before the lockdown to 82.2% during the lockdown). 40 80 Sixty-nine per cent of Italian children and adolescents reported having more difficulty in falling asleep during the lockdown. 81 In contrast, Chinese preschoolers and teenagers had better quality sleep during the COVID-19 lockdown compared with before the pandemic. 73 74 Children in Canada and Poland also experienced better quality sleep during the lockdown. 27 51 79 A multicountry longitudinal study among children aged 3-5 years old reported no significant change in the proportion of children with poor sleep quality from before to during the lockdown. 26 Movement behaviours among children and adolescents with health conditions Fourteen studies [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] assessed the impact of COVID-19related lockdown on movement behaviours (physical activity: 10, screen time: 9, sleep duration: 4, and sleep quality: 4) of children with health conditions such as autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), type 1 and type 2 diabetes, obesity, physical disability, neurodevelopmental disability, psychiatric disorder, fragile X-syndrome and dental wear.

Almost all the studies reported that the movement behaviours of children and adolescents with health conditions worsened during the lockdown, except two studies that reported no significant change in physical activity 85 and sleep quality. 85 92 Italian children with obesity spent 2.30 hours less per week in sports during the lockdown than before the lockdown. 94 Australian children with ADHD also had less exercise (OR 0.4, 95% CI 0.3, 0.6, p=0.003) during the pandemic than before the pandemic. 95 In Italy, children with obesity spent 4.85 hours more on screen daily during the lockdown, reaching an alarming level of 7.61 hours per day of screen time. 94 Canadian children and adolescents with ASD increased their daily screen time from 3.3 hours before the lockdown to 6.9 hours during the lockdown. 86 Turkish children with ASD showed increased sleep problems during the lockdown (total Children's Sleep Habits Questionnaire score: 47.82 before the lockdown vs 50.80 during the lockdown, p=0.001). 96 In Italy, the proportion of children with Fragile-X Syndrome often having difficulty falling asleep increased from 6% before the lockdown to 15% during the lockdown. 89 Certainty of evidence Table 5 presents the strength of evidence from quantitative studies on the outcomes. Moderate evidence was observed for decreased physical activity and increased screen time during the COVID-19 lockdown than before the lockdown. The evidence for sleep duration and sleep quality was inconclusive. 

of the studies observed a decline in physical activity level among children and adolescents, while some reported no change, and one reported an increase in physical activity during the lockdown. Furthermore, all the studies observed increased screen time in children and adolescents during the lockdown. Most of the studies reported an increase in sleep problems during the pandemic than before the pandemic. Such changes in movement behaviours applied to both apparently healthy children and adolescents, and those with health conditions, with more profound effects observed in the latter group.

According to the majority of the studies in this review, children and adolescents were less active during the COVID-19 restrictions. COVID-19 lockdown created a disabling environment for children to engage in physical activity through home confinement orders and closure of schools and recreation facilities. 6 99 Among the countries included in this review, Spanish and Brazilian children and adolescents saw the biggest decline in physical activity. 40 52 57 58 These differences in the pattern of physical activity could be attributed to the effect of COVID-19, the degree of lockdown restrictions and the household environment. Spain and Brazil were among the hardest-hit countries by the COVID-19 pandemic, with many COVID-19 infections and deaths. 100 The lockdown restriction in Spain was stringent, and children were not allowed to go outdoors. 3 Most Brazilian children were living in apartments and had limited access to outdoor space for physical activity and sports. 58 Evidence has shown that the availability of bigger outdoor space at the place of residence can positively influence physical activity among children and adolescents both during and before lockdown. 101 102 Meanwhile, children and adolescents in some countries could maintain or even increase their physical activity levels during the lockdown restrictions. In Western Australia, children's physical activity levels did not change from before to during the pandemic. 20 German children and adolescents were more active during the COVID-19 restrictions than before the restrictions, and the proportion of the children and adolescents adhering to physical activity guidelines increased during the lockdown compared with before the lockdown. 19 Several factors might explain these findings, such as the nature of lockdown restrictions, the methodological differences in assessing physical activity and the environment. The lockdown in Western Australia was relatively short, and people were allowed to go outdoors for exercise. 20 Similarly, the lockdown restrictions in Germany were moderate, allowing outdoor activities if done alone or with family members. 19 These two studies in Western Australia and Germany tracked various forms of physical activity across different settings. 19 20 People in Australia were encouraged to exercise during the restrictions through constant messaging by government officials. 20 They also had a relatively conducive household environment for active indoor and outdoor play for children. 20 In all the studies, the screen time of children and adolescents increased during the COVID-19 lockdown. Schools were closed, and children were confined inside their homes during the lockdown, resulting in more free time. This increased free time and drastically reduced outdoor time could have led children to spend more time on screen for recreation. Parents' work conditions during the lockdown might also have affected children's screen time. Many working parents were asked to telework 37 §Evidence based on quality, number and the outcome of the studies: strong=provided by generally consistent findings in multiple highquality quantitative studies; moderate=generally consistent findings in one high-quality quantitative study and one low-quality study or in multiple low-quality studies; inconclusive=only one study available or inconsistent findings in multiple studies 37 BMJ Global Health from home during the lockdown. Children's screen use behaviour might have been influenced by that of the parents. Children might also have been encouraged by parents to spend their free time on screen to provide a quiet work environment at home for the parents. The relationship between family environment and children's behaviour has been well established. 103 Confined children and adolescents might use electronic devices more frequently to connect with their peers via social media. 104 Similar to physical activity, a pattern can be observed in children's increased screen time related to the degree of restrictions the children faced. The increase in screen time was higher for children in countries with strict lockdowns, such as Spain, Brazil and Turkey, 3 52 58 68 while it was comparatively lower in countries with mild restrictions, such as Germany and Australia. 19 20 In nearly half of the studies, children and adolescents increased their sleep duration, and in most of the studies that reported bedtime and wake-up time, children went to bed later and woke up later during the lockdown than before the lockdown. Such change in sleep patterns can be seen as normal because the schools were closed, and children had more free time to relax. They also did not have to wake up early during the lockdown as they did not have to rush to the school. Children were also found to sleep longer during the weekends and holidays before the pandemic. 12 However, relatively longer sleep duration and later bedtime and wake-up time might be a problem for children because they will find it difficult to return to their normal routine once schools resume after the lockdown. This review has several limitations. First, empirical evidence could not be generated using a meta-analysis. We observed a wide heterogeneity across studies in terms of outcome indicators and their measurements. We also did not have sufficient studies to pool the data for a meta-analysis. Second, a concrete objective measurement of the exposure was difficult. Countries included in this review had different forms and varying degrees of lockdown restrictions. Some of the articles also did not provide sufficient information about the lockdown. We had to base our analysis on the information provided in the article because it was difficult to track the detailed information on lockdowns in different regions of the countries as it changes quickly. However, we tried to categorise the severity of lockdown based on the information provided in the articles. Third, since the studies using objective (device-based) methods for outcomes assessment were very few, we combined them with those using subjective methods. Fourth, most studies reported data from high-income economies, and no study reported data from a low-income economy. This might limit the generalisation of the findings of this review to low-and middle-income settings. Next, most studies collected data using online self-reported questionnaires, as it was the most feasible option during lockdown restrictions; hence, this might have reduced the reliability and validity of the data. Finally, most of the studies used a cross-sectional design, generating a relatively lower quality of evidence. Despite these limitations, this study has some strengths. To the best of our knowledge, it is the first study to comprehensively review the impact of COVID-19 lockdown restrictions on children and adolescents' movement behaviours. Furthermore, this review searched articles from a wide range of databases at three time points and included a large sample of articles from various countries and territories worldwide.

Lockdown restrictions to curb the spread of COVID-19 had a mostly negative effect on children and adolescents' movement behaviours worldwide. Children spent less time on physical activity and more time on screens during confinement than before the pandemic. However, children and adolescents facing milder restrictions, such as in Germany and Western Australia, where they were allowed to go outdoors for exercise while maintaining social distance, were physically more active and used screens less than those under stricter lockdowns, such as in Spain. Children and adolescents tended to sleep longer hours, with later bedtime and wake-up time during the pandemic than before the pandemic. Acknowledging that unhealthy movement behaviours can negatively affect children and adolescents' physical, social and psychological health, appropriate actions are essential from all the relevant stakeholders. The findings from this review suggest that the authorities should carefully consider the negative consequences of the measures to contain the spread of infections on the healthy movement behaviours of children and adolescents while applying them, and such measures should be introduced in a way that would have the least effect on children and adolescents' healthly movement behaviours. Healthrelated organisations and authorities should emphasise the importance of remaining physically active, especially during a lockdown, and suggest possible ways to do so. Schools should consider having online physical education lessons to engage children in physical activity. Parents should encourage and support their children to engage in physical activity while maintaining social distance. They should also motivate and provide a conducive environment for their children to spend their time in creative activities rather than using the screens. Further studies with robust study designs should be conducted to assess the impact of COVID-19 lockdown on the healthy movement behaviours of children and adolescents. More studies from low-income and middle-income countries could help in improving the understanding of the impact.

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