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Impact of the COVID-19 Pandemic on Sedentary Time and Behaviour in Children and Adults: A Systematic Review and Meta-Analysis

The aim of this meta-analysis was to quantify the change in sedentary time during the COVID-19 pandemic and its effect on health outcomes in the general population. One thousand six hundred and one articles published after 2019 were retrieved from five databases, of which 64 and 40 were included in the systematic review and meta-analysis, respectively. Studies were grouped according to population: children (<18 years), adults (18–64 years) and older adults (>65 years). Average sedentary time was calculated, with sub-analyses performed by country, behaviour type and health outcomes. Children were most affected, increasing their sedentary time by 159.5 ± 142.6 min day−1, followed by adults (+126.9 ± 42.2 min day−1) and older adults (+46.9 ± 22.0 min day−1). There were no sex differences in any age group. Screen time was the only consistently measured behaviour and accounted for 46.8% and 57.2% of total sedentary time in children and adults, respectively. Increases in sedentary time were negatively correlated with global mental health, depression, anxiety and quality of life, irrespective of age. Whilst lockdown negatively affected all age groups, children were more negatively affected than adults or older adults, highlighting this population as a key intervention target. As lockdowns ease worldwide, strategies should be employed to reduce time spent sedentary. Trial registration: PROSPERO (CRD42020208909).


Introduction
Sedentary behaviour, defined as any activity in a seated or reclined posture expending ≤1.5 metabolic equivalents (METs, [1]), is suggested to be an independent short-and long-term risk factor for markers of adiposity, cardiovascular disease and type II diabetes mellitus [2][3][4]. Similarly, prolonged bouts of uninterrupted sedentary time across the day are associated with significant health risks [3,5] that have been shown to persist irrespective of physical activity (PA) levels [1,6,7], although this remains contentious [8,9]. Indeed, even 10 min of uninterrupted sedentary time has been reported to decrease insulin sensitivity and glucose tolerance and increase circulating triglyceride levels [1]. Of concern, however, the average North American child (8-18 years) engages in 75 h week −1 (or 10.7 h day −1 ) of multimedia use [10,11], with comparable levels reported in European [12] and Asian [13] children. Similar levels of sedentary time (up to 12.3 ± 1.4 h day −1 ) have been reported globally in adults [3,4]. Sedentary lifestyles, and the identification of strategies to reverse them, represent a significant public health challenge [14]. Moreover, the need to understand sedentary time and behaviour, and their relationship(s) with health outcomes, may be more important than ever with the emergence of novel Coronavirus 2019 disease .
Since the pandemic was announced in December 2019, there have been in excess of 167 million cases and 3.5 million deaths across 216 countries, as of 24 May 2021 [15]. Whilst the global response has been far from homogeneous most countries have adopted some form of social distancing, homestay (or lockdown) requirements, self-isolation or quarantine measures to limit COVID-19 transmission, and relieve pressure on health care services [16]. Indeed, in April 2020, over 50% of the global population were subject to some form of government restrictions [15], many of which may have had unintended deleterious health consequences. More specifically, homestay strategies may have increased sitting and screen time, due to children participating in online learning and adults working from home [16], whilst decreasing opportunities to break-up prolonged periods of sedentary time/behaviour. The effects of COVID-19 and subsequent restrictions on habitual PA levels have received substantial attention, with a recent review reporting decreased levels of PA globally which was attributed to social distancing measures [17]. However, no review to date has considered the impact of these restrictions on sedentary time, or the associated behaviours.
Meyer et al. [18] reported that ≥8 h day −1 of screen time was associated with a greater likelihood of symptoms of depression, loneliness, and stress during the COVID-19 pandemic in 3052 American adults. However, in the same study, total sitting time was not associated with any mental health outcome [18], in accord with Ugboule et al. [19] who reported no associations between sedentary time and emotional well-being in 9142 similarly aged adults. Studies examining the effect of COVID-19 restrictions on sedentary time in children are also conflicting. Indeed, Kang et al. [20] reported trivial associations between sedentary time and mental health outcomes in 4898 Chinese adolescents (16.3 ± 1.3 years), whereas Lu et al. [21] reported a positive association between sedentary time and risk of insomnia, depression, and anxiety in 965 Chinese adolescents (15.3 ± 0.5 years). Moreover, it is pertinent to note the potential for geographically specific variations in this relationship between sedentary time and health outcomes, thereby limiting the conclusions that can be drawn on the basis of single-country analyses. Therefore, a review is urgently needed to consolidate our understanding of COVID-19's impact on sedentary time/behaviour and associated health outcomes and thereby highlight avenues for future interventions and research.
Therefore, the aim of this review was to assess the influence of COVID-19 and associated government restrictions on sedentary time and/or behaviour and physical, mental, and social health outcomes in the general population. A secondary aim was to examine the strength of association between sedentary time and/or behaviour and health outcomes during the COVID-19 pandemic.

Search Strategy and Inclusion Criteria
This systematic review protocol was registered on PROSPERO (registration number: CRD42020208909) and conducted in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [22,23]. An online search was conducted on 12 January 2021 across the following databases: EBSCOhost, Medline, SPORTDiscus, Scopus, and Web of Science Core Collection. A date limit was set as 2020-2021 to ensure that only articles concerning COVID-19 were collected. Across these databases, the key search terms were modified to individual requirements, with Boolean and MeSH terms used to search the following terms and their variations: "sedentary time", "sedentary behaviour", "screen time", "sitting time", "sedentary posture" AND "COVID-19", "SARS-CoV", "2019 corona-virus". The full search terms can be found in the online supplementary material. Two authors (AR and RK) initially screened all abstracts independently before reviewing full-text articles for inclusion. In cases where disagreements regarding the inclusion of a study were unable to be resolved, LS was consulted to reach a consensus, which occurred on three occasions. Of the three articles where there were disagreements, one was included in the final review.
All studies assessing any type of sedentary behaviour or sedentary time (time spent below 1.5 METs but without verification of posture) using either subjective (questionnaires or interviews) or device-based (accelerometers or inclinometers) measures, in any population (children: <18 years of age, adults: >18 years of age, or older adults: >65 years of age), irrespective of methodological approach (cross-sectional, cohort, or longitudinal study designs), were included. Furthermore, adequate reporting of the restrictions in place at the time of data collection was required for inclusion to enable tentative comparisons to be made between geographical regions. All studies involving human participants and written in the English language which met the specified criteria were included, with any non-peer reviewed grey literature, including conference papers and theses, excluded. To be included within the meta-analysis studies had to provide data from before and during the COVID-19 pandemic so the impact of the pandemic could be assessed. Moreover, commentaries examining the potential detrimental effects of sedentary time and/or behaviour during the COVID-19 pandemic were also excluded. The initial search gathered 1601 results (903 after the removal of duplicates), from which 828 were excluded during the title and abstract screening phase. Following full-text review, 64 articles were retained and included within the systematic review and 40 were utilized within the meta-analysis ( Figure 1).

Data Extraction, Quality Assessment, and Risk of Bias Appraisal
Data extraction from all included full-text articles was completed to obtain the following information: authors and year of publication, number and age of participants, country of study, COVID-19 restrictions in place at the time of data collection, sedentary time/behaviour measures, health outcome measures reported (if any), information required to assess risk of bias, and main results (Tables 1 and 2

Data Extraction, Quality Assessment, and Risk of Bias Appraisal
Data extraction from all included full-text articles was completed to obtain the following information: authors and year of publication, number and age of participants, country of study, COVID-19 restrictions in place at the time of data collection, sedentary time/behaviour measures, health outcome measures reported (if any), information required to assess risk of bias, and main results (Tables 1 and 2). All researchers contributed to the synthesis of data. Risk of bias was assessed using the Cochrane risk of bias tool as described in the Cochrane Handbook 5.1.0 for systematic reviews [24]. Briefly, for every included study, risk of bias was classified as 'High', 'Moderate', 'Low' or 'Unclear/Not reported' in the following areas: detection bias, attrition bias, selection bias, performance bias, selective reporting bias and other sources of bias. A brief rationale for the decision is included in the supplementary material, in line with previous studies [25,26], with the full risk of bias table available in Supplementary Information Table S1 and S2.
The quality of evidence for each of the included studies was decided in a systematic manner with the aid of the Grading of Recommendations Assessment Development and Evaluation (GRADE) framework [27], as used in previous reviews of this type [25,26]. The GRADE framework allows for the classification of research articles into four distinct categories ('High', 'Moderate', 'Low', and 'Very Low'). Any study including a randomised recruitment and/or a longitudinal design starts at 'High', with all other study types and designs starting at 'Low'. The quality of evidence was then downgraded if there were serious limitations hindering the interpretation of the study, such as high risk of bias, unvalidated data collection methods, and convenience sampling techniques [27]. Conversely, the quality of evidence was upgraded if there is no cause for the downgrading of the study and a large effect size and/or a dose-response relationship was evident within the study [27]. All included studies were synthesised in a systematic approach examining the effect of COVID-19 on overall sedentary time, and specific sedentary behaviours where appropriate. All results were divided into children, adult, and older adult specific segments due to the population-specific sedentary behaviour guidelines [14,28] and the potentially different impacts of government restrictions on these populations.
All meta-analyses were conducted in R (R Studio v1.2.2019, R Studio, Boston, MA, USA) using the meta and metagen packages and their dependencies. Where pre-and post-COVID data were available, the standardised mean difference (SMD) was calculated using the formula: difference between means/standard deviation of outcome [29]. Prior to calculating the SMD, all sedentary time and behaviour measurements were converted into minutes per day (mins day −1 ) to ensure all variables were reported on the same nominal scale. Time spent sedentary during COVID-19 was determined based on those studies that specifically reported the sedentary time of participants experiencing government restrictions and the post data in longitudinal studies. Subsequently, the average sedentary time between studies, and the pooled standard deviation, were calculated. Meta-analyses were conducted separately for both child, adult, and older adult data, and between sexes where the data were available, so that tentative inter-population comparisons could be made.    pre-COVID to 490.0 ± 25.0 min day −1 during COVID

Discussion
The aim of this meta-analysis was to explore the effects of the COVID-19 pandemic and the associated government restrictions on sedentary time and sedentary behaviour.
A key finding was that sedentary time was substantially increased, irrespective of the restrictions imposed or population. More specifically, children increased their sedentary time the most during the pandemic, although their overall time spent sedentary was still lower than observed in adults. There were no significant sex differences in sedentary time across the pandemic irrespective of age. Finally, increases in sedentary time as a result of the pandemic were weakly, but significantly, related with QoL and mental health, with higher time spent sedentary associated with greater anxiety and depression.

Children's Sedentary Time
The currently available evidence suggests that children increased their overall sedentary time by 159.5 min day −1 during the COVID-19 pandemic, although it is pertinent to note the large standard deviation (±142.6 min day −1 ). This therefore highlights the huge disparity in response in this population. Indeed, these results suggest that some children may have accrued similar sedentary time on weekdays during restrictions to during their normal school routines. Whilst it could be postulated that those exhibiting smaller absolute increases in sedentary time may have been characterised by a lower baseline time spent being sedentary and thus the relative increase was still similar, it is of concern to note that some children may have increased their sedentary time by more than five hours per day. Potential reasons for this large discrepancy in sedentary time may be disparities in access to gardens and green spaces during confinement, limiting opportunities to break-up prolonged sedentary time [31,87,88]. More specifically, Akpinar [89] reported that the distance between urban green spaces and the home was significantly correlated with children's screen time, even after covarying for age and socioeconomic status [SES; [87,90]. Whilst the determinants of sedentary time and behaviour are multifaceted, SES is a critically important factor determining PA and sedentary time in children [90], with COVID-19 exacerbating pre-existing inequalities. Furthermore, other social factors, such as a low parental education level, children with overweight/obese parents [31], and children of parents with high anxiety regarding COVID-19 [37], were all correlates of an increased sedentary time. The finding that screen time accounted for~47% of total sedentary time was expected given that the majority of countries worldwide have now adopted online learning methods [52].
Despite the apparent increase in sedentary time during the pandemic in children observed in the present meta-analysis, the total sedentary time determined in this review (383.9 ± 138.2 min day −1 ) was nonetheless in accord with [91,92], or lower than [13,93], the figures reported prior to the pandemic. This is likely to be predominantly due to a reliance on subjective recall measures during the pandemic [94]. More specifically, the reliability of recall measures, especially in children, is limited, with boys typically overestimating the amount of PA and sedentary time they perform [95]. Furthermore, children's misrepresentation of time potentially exaggerates recall bias [95], and that the volume of sedentary time is only one component of a wider composition of daily movement behaviours which are critical for current and future health outcomes [1,91,96,97]. It is also noteworthy that the meta-analysis in children was conducted on only six studies that provided pre-post data, accounting for only 15.0% of the total review population [27,[29][30][31][32]38]. Caution must therefore be taken when extrapolating the findings from this meta-analysis to the wider population.
Despite the wide discrepancy in both children's absolute and increases in sedentary time, there were no sex differences in cumulative sedentary time, which may be considered to be unsurprising given that both boys and girls have been equally affected by lockdown measures. However, pre-COVID-19, it was consistently reported that girls were more sedentary than similarly aged boys [12,93,98,99]. This may therefore indicate that the pandemic had a greater impact on sedentary time in boys than girls. Indeed, despite accruing less overall sedentary time than girls, boys consistently reported an increased screen time [100], with lockdown restrictions likely exaggerating these observations which may explain the lack of sex difference. It is also pertinent to note that previous research has consistently reported that boys are more active during school hours than girls, indicating the social element of PA may be of greater importance to boys [101]. Consequently, the social confinement associated with COVID-19 restrictions may have had a greater impact on boy's PA levels and subsequent sedentary time. The lack of sex difference may be attributable to different data collection methods between studies, and differences in questions asked, which have varying degrees of reliability [102].
Three studies examined the association of sedentary time with health outcomes in children with conflicting results [20,21,32]. More specifically, Kang et al. [20] reported no association between total sedentary time and perceived mood in 4898 Chinese adolescents (16.3 ± 1.3 years), whereas Lu et al. [21] reported those with a sitting time of ≥4 h day −1 had a greater risk of experiencing anxiety, depression and insomnia (OR: 1.35-1.87) in a similar sample of 953 Chinese adolescents (15.3 ± 0.5 years). These differences cannot be attributed to cultural, age or lockdown restrictions and may therefore be indicative of the protective role that the maintenance of PA has on mental health during times of adversity, although more data is needed to confirm this postulation. However, the discrepancy may also be due to differences in the measures of sedentary time used, with Kang et al. [20] reporting total sedentary time while Lu et al. [21] focused specifically on sitting time. Given that the influence of being sedentary on health outcomes is well evidenced to be dependent on specific type of sedentary behaviour [5,26,92,103], further inter-study comparisons are therefore precluded.

Adults and Older Adults
Overall, adults increased their sedentary time by 126.9 ± 42.2 min day −1 , spending a cumulative 510.5 ± 167.9 min day −1 in sedentary behaviours, which was significantly higher than children (+ 127 min day −1 ). The reasons for this are not immediately clear and are likely multifaceted. One possible reason for the higher absolute sedentary time in adults compared to children could be due to their higher sedentary time pre-COVID possibly due to sedentary occupations [104]. Moreover, adults who adhered strictly to guidelines experienced an additional increase of 60 min day −1 in sedentary time during the pandemic than those who did not [44]. Furthermore, adults with higher levels of COVID-19 related anxiety were more likely to demonstrate a higher sedentary time compared to those with low anxiety [37]. Additionally, the lack of commute to work due to lockdown and homeworking requirements in most countries and the closure of sporting facilities (gyms, swimming pools etc) is likely to reduce PA opportunities to a greater extent in adults than children. Indeed, it is well accepted that adults complete PA in a structured, planned manner [8,105] and therefore COVID-19 is likely to have a bigger impact upon their PA and sedentary time levels. Taken together, this suggests that children and adults may experience different effects stemming from COVID-19 restrictions and therefore a one-size fits all approach to minimise the health detriments is unlikely to be effective for both populations. Similar to children, there were no sex differences in total sedentary time in adults suggesting men have been disproportionately affected by the effects of COVID-19 restrictions compared to women. Potential reasons for the lack of sex differences include women choosing to partake in physical activity closer to the home [106] which may have been less impacted and the greater proportion of men who regularly partake in team sport activities [107] which were suspended during the pandemic.
Older adults were the most sedentary group included within this systematic review and meta-analysis, with sedentary time totalling 586.3 ± 25.2 min day −1 . However, they were also the least impacted by COVID-19, with their sedentary time only increasing by an average of 46.9 ± 22.0 min day −1 . This may be due to their reduced likelihood of being in employment and lower tendency to be highly active prior to COVID-19 [107]. Similar to children, there were no significant sex differences in overall sedentary time, despite females engaging in more sedentary time pre-COVID-19 [4,6]. This may therefore similarly suggest that COVID-19 may have had more of an influence on males' sedentary time than females' but more evidence is needed to confirm this postulation.
The regional trends in this meta-analysis were discordant with previous research which reported that Asian adults were the most sedentary [108] and potentially indicate the effect of different lockdown strategies on sedentary time and behaviour. More specifically, China enforced strict, localised lockdowns in areas of infection, and lesser restrictions in areas of lower infection rates, as opposed to blanket national restrictions [109]. Whilst it could be speculated that including participants from non-lockdown regions potentially adds bias within the data, it also provides insights as to how COVID-19 may be managed whilst minimising the undesirable health consequences of lockdown conditions. However, it must be noted that there are a multitude of other factors that influence sedentary time and behaviour [5,110], therefore examining the specific influence of different governmental restrictions globally remains challenging.
Twelve studies examined the effect of sedentary time and behaviour on health-related outcomes in adults [18,45,46,48,61,62,64,68,71,82,84,85]. More specifically, five considered global mental health [18,48,61,84,85] and generally reported a negative association between sedentary time and global mental health, concordant with previous research [111]. However, Stieger et al. [62] reported that sedentary time was positively associated with perceived levels of stress but not overall mental health score, and therefore other lifestyle factors may also be important for the maintenance of mental health during lockdown. Other lifestyle factors noted within the current review include diet [45,51,71,79], physical activity [59,111] and minimising tobacco and alcohol consumption [48,58,79]. Similar relationships were observed regarding the effect of sedentary time on quality of life, [58,62,65,87], depression symptoms [33,82], and subjective well-being [52], highlighting the significant, and diverse, negative consequences of excessive sedentary time. Strategies need to be employed to encourage the breaking up of prolonged sedentary periods and the re-opening of sports facilities and green spaces needs to be prioritised when restrictions are eased for general health and well-being.

Strengths and Limitations
Whilst there are many strengths of this review, including the meta-analysis to quantify changes in sedentary time during the COVID-19 pandemic, the identification of intercountry differences, and the inclusion of both children and adults, there are some limitations which must be acknowledged. First, the global pandemic is still ongoing, with scientific knowledge in this area being updated weekly, which may impact the overall findings. Nevertheless, this review consolidates our current understanding and highlights areas which require further research. Secondly, the majority of studies did not comprehensively report the lockdown restrictions currently in place during the time of data collection, using phrases such as 'lockdown' or 'home-stay' requirements which were interpreted differently in almost every country [15]. Therefore, no evidence is available to assess the impact of specific lockdown restrictions on sedentary time and behaviours. Additionally, little information was able to be synthesised within this review on the effects of specific sedentary behaviours which are purported to have differing health effects [3,4,58]. Moreover, the reliance on subjective recall data, especially in children, has recognised limitations and questionable validity [102] and therefore the results of this meta-analysis should be interpreted as an estimation only regarding the effect of COVID-19 on sedentary time in children, adults, and older adults. Finally, SES, a strong correlate of sedentary time, was not able to be controlled for within this meta-analysis due to a paucity of available data and needs considering in future work.

Conclusions
In conclusion, the COVID-19 pandemic resulted in increased sedentary time irrespective of lockdown conditions or population. Of importance, greater increases in time spent sedentary were suggested to be evident in both boys and men, suggesting that they have been disproportionally affected by lockdown restrictions. Moreover, increases in sedentary time as a result of COVID-19 restrictions were weakly, but significantly, correlated to poorer QoL, global mental health, depression, and likelihood of seizures. Therefore, as restrictions ease there should be a focus on reengaging everybody with PA and encouraging the breaking up of prolonged sedentary periods to improve both physical and mental well-being.

Data Availability Statement:
The data that support the findings of this study are available from the corresponding author upon reasonable request.