The COVID-19 Pandemic and Daily Steps in the General Population: Meta-analysis of Observational Studies

Background: The COVID-19 pandemic has the potential to accelerate another pandemic: physical inactivity. Daily steps, a proxy of physical activity, are closely related to health. Recent studies indicate that over 7000 steps per day is the critical physical activity standard for minimizing the risk of all-cause mortality. Moreover, the risk of cardiovascular events has been found to increase by 8% for every 2000 steps per day decrement. Objective: To quantify the impact of the COVID-19


Introduction
Physical activity has been crucial for preventing and treating multiple chronic health conditions [1,2] and premature mortality [3,4], while the number of daily steps is a primary proxy measure for physical activity [5]. Daily step goals can be tailored to meet individual needs and when used with a monitor are effective in promoting physical activity [6]. Previous studies have found that higher daily steps are associated with multiple health benefits, such as lower risk of cardiovascular disease [7], diabetes [8,9], and all-cause mortality [10][11][12][13]. For example, the risk of all-cause mortality in adults shows a declining trend with an increase in daily steps and plateaus at approximately 7000 steps per day [12,13]. In contrast, a decrease in daily steps is responsible for a range of unhealthy outcomes, such as increased risk of cardiovascular disease [14], compromised muscle metabolism [15], and elevated systemic inflammation [15,16]. Specifically, the risk of cardiovascular events was reported to increase by 8% for every 2000 steps per day decrement [14]. A sharp reduction in daily steps might also reduce leg lean mass and induce impairments of myofibrillar protein synthesis in healthy elderly individuals, accompanied by increased circulating inflammatory markers [15,16].
Although global responses were far from homogeneous, most countries adopted restriction measures in varying forms to limit the transmission of COVID-19, such as physical distancing, working from home, and closing schools [17]. These measures have resulted in unprecedented changes in all aspects of daily life [18], and physical activity is certainly one of the aspects being most affected. Recently, several studies reported a significant decline in daily steps during the confinement period of the COVID-19 pandemic [19][20][21][22][23]. One study found that the daily steps of young adults in Singapore decreased by 42% on average during the lockdown period compared with the time before the pandemic [20]. Another study reported a sharp, 30% reduction in daily steps in Chinese citizens and a significant increase in the proportion of adults with frequent low daily steps (≤1500 steps/day for ≥14 days) during the confinement period [19]. By contrast, one study reported only a 5% reduction in daily steps 30 days after the start of lockdown in Australia [22]. These findings indicate the possibility of geographically specific variations in the relationship between COVID-19-related restrictions and daily steps, which limits the generalization of conclusions drawn from single country-based analyses. Therefore, a systematic review is needed to consolidate the current understanding of the impact of COVID-19 on daily steps in order to enlighten future interventions and research directions. In addition, a few studies have also evaluated whether the impact of COVID-19 on physical activity varied by gender. One study suggested that men had more reduction in time spent in moderate-vigorous physical activities and a larger increase in sedentary behaviors than women during the pandemic [24]. However, another study failed to confirm this finding [25].
To fill this knowledge gap, we conducted a meta-analysis of observational studies to quantify both global and regional impacts of confinement during the COVID-19 pandemic on daily steps in the general adult population, and we also examined whether the decline in daily steps differed between men and women.

Protocol and Registration
The MOOSE (Meta-analysis Of Observational Studies in Epidemiology) [26] and PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2020 [27] guidelines were followed for reporting this study (Multimedia Appendix 1). The protocol for this study was prospectively registered in the PROSPERO database (CRD42021291684).

Search Strategy
A preliminary search was conducted on PubMed, EMBASE, and Web of Science to retrieve studies that reported daily step data both before and during the confinement period of the COVID-19 pandemic in the general adult population published before November 22, 2021. Further, an updated search was performed on February 11, 2023, to add recently published articles. The detailed search strategy is listed in Multimedia Appendix 2 [28][29][30][31]. The International Standard Randomized Controlled Trial Number Register (ISRCTN) and the World Health Organization COVID-19 database were also searched for potential gray literature. The reference lists and citing articles of relevant literature on this topic were also checked to find possible studies that could be included in this research. The language of publication was not restricted.

Eligibility Criteria and Study Selection
We included observational studies that reported daily steps before and during the confinement period of the COVID-19 pandemic in the general adult population. The reference period was restricted to ≤2 years before the time points when the government implemented the confinement measures. Further eligibility criteria are listed in Textbox 1. Textbox 1. Eligibility criteria for study screening.

Inclusion criteria
Study type: Observational studies Participants: General adult population (average age over 20 years) Outcomes: Daily steps, measured using monitoring devices including wearable physical activity trackers (eg, pedometers, accelerometers, smartwatches, and smart bands) and smartphones mobile apps (eg, iPhone Health, Google Fit, WeChat, and Exercise Health) Other criteria: Daily step data collected both before and during the confinement period of COVID-19. The reference period was restricted to ≤2 years before the time points when the government implemented the confinement measures

Exclusion criteria
Study type: Any non-observational study (eg, reviews, randomized controlled trials, and case reports), conference abstracts Participants: Children, adolescents, athletes, specific patient groups, participants with particular conditions (eg, pregnant women or elderly individuals at high risk of falls) Outcomes: Data other than daily steps (eg, physical activity measured using questionnaires alone or data measured by wearable devices that are classified as light, moderate, or vigorous physical activity) Other criteria: Studies offering financial incentives that may promote physical activity (eg, rewards for individuals who achieve predetermined goals through monitors), studies lacking available data for meta-analysis Two independent reviewers (LS and WR) screened all titles and abstracts. The full text of potentially relevant literature was further evaluated. A third reviewer (ZW) arbitrated the decision if a consensus was not reached.

Data Extraction
Two authors (LS and WR) extracted the following data independently: study design, country and continent (Africa, Asia, Europe, North America, South America, and Oceania) where the study was conducted, the sample size used for daily step analysis, participant characteristics (ie, mean age and female ratio), monitoring devices used to measure daily steps, the algorithm used to analyze daily steps, data collection duration, and COVID-19 restriction measures by the government at the time of data collection. The outcomes of interest were the total number of daily steps before and during the confinement period of COVID-19 and the percentage change between the 2 periods. If not reported, the mean (SD) of the outcome was estimated based on the methods provided by the Cochrane Handbook [32]. If data needed to be extracted from graphs, the GetData digitizer was used [33]. This tool has been validated and has good accuracy and precision for data extraction; it has been used in meta-analysis by previous studies [34]. Disagreements, if any, were resolved by consulting with a third reviewer (ZW). When any desired information related to daily steps was missing or unclear, the corresponding author was contacted via email to request or confirm the relevant data, as appropriate. If the data could not be obtained, the study was excluded from the meta-analysis.

Risk of Bias and Quality of Individual Studies
The modified Newcastle-Ottawa Scale (NOS) for applicable observational studies was used to assess the methodological quality and risk of bias in each study [28][29][30]. Specifically, the modified NOS consists of 3 domains: selection (maximum 3 stars), comparability (maximum 2 stars), and outcome (maximum 2 stars). Therefore, 1 study can be awarded a maximum of 7 stars. Studies with 6 to 7 stars were rated as high quality, those with 5 stars were rated as moderate quality, and those with 4 or fewer stars were rated as low quality [29]. Two reviewers (LS and ZW) rated the methodological quality of each study independently, and discrepancies, if any, were discussed for consensus or resolved by consulting a third reviewer (YW).

Data Synthesis and Analysis
A random effects meta-analysis was conducted using Stata software (version 14.0; StataCorp). The change in daily steps was calculated using the mean difference (MD) with the 95% CI between the mean (SD) of daily steps before and during the confinement period of COVID-19. The Cochran Q statistic of the inconsistency index (I 2 ) was used to test statistical heterogeneity across studies [32,35]. An I 2 value of more than 75% indicated high heterogeneity [32]. Publication bias was assessed with a funnel plot and further evaluated with the Egger test [36]. To test the robustness of the findings on the primary outcome (ie, the number of daily steps), we performed 3 sensitivity analyses. First, we conducted an analysis that eliminated each study one at a time. Second, we performed an analysis that removed the studies rated as having low methodological quality. Third, we performed an analysis that excluded the studies with a small sample size (less than 140) based on the recommendations of Dunton and colleagues [37]. Finally, we also conducted subgroup analyses according to country, continent, and gender.

Quality Assessment
Thirteen studies (65%) were rated as having moderate to high methodological quality (Multimedia Appendix 2, Table S1). Considering the widespread weaknesses of small sample size, imbalanced gender ratio, limited age range of the study sample, and poor nationwide representativeness, only 2 studies were rated as having national representativeness of the exposed cohort (ie, samples during the confinement period of COVID-19). Thus, 10% of the included studies received 3 stars in the selection dimension, 30% received 2 stars in the comparability dimension, and 60% received 2 stars in the outcome dimension.

Quantitative Synthesis
As shown in Figure 2, the proportion of studies with subjects with optimal daily steps (ie, ≥7000 steps per day) declined from 70% before the pandemic to 25% during the confinement period. The change in daily steps between the 2 periods ranged from -5771 to -683. The pooled MD from the random effects pooled analysis was -2012 (95% CI -2805 to -1218; Figure 3), with significant heterogeneity among studies (P<.001; I 2 =97.6%).

Principal Results
Our study quantified the change in daily steps during the confinement period of COVID-19. The proportion of studies with subjects with optimal daily steps (ie, ≥7000 steps/day) declined from 70% before the pandemic to 25% during the confinement period, and the average number of daily steps was reduced by 2000. Our results also suggest a possible inequality in physical activity across countries, whether before or during the pandemic. However, given that most included studies lacked sufficient nationwide representativeness, this difference should be interpreted cautiously. Furthermore, there was no apparent gender difference in the decline in daily steps before and during the confinement period of COVID-19.

Possible Explanations and Clinical Implications
The population-level trends in daily steps during the confinement period of COVID-19 may reflect public panic about the virus and adherence to confinement measures (ie, physical distancing and sheltering in place) [55,56]. Our findings are not surprising given that COVID-19 restriction measures deprived the general population of many opportunities for physical activity, such as commuting, shopping, sports, and vacations or trips. In addition, the observed differences in the change in daily steps across studies may reflect regional variations in enforcement and behavioral changes [57,58]. Socioeconomic inequalities might also influence such variations among regions and disparities in the ability to engage in or access recreational physical activity within areas [59].
Recent studies indicate that over 7000 steps per day is the critical physical activity standard for minimizing the risk of all-cause mortality [12,13]. Moreover, the risk of cardiovascular events increases by 8% for every 2000 steps per day decrement [14]. We found that daily steps declined by 2000, and half of the included studies reported that average daily steps declined to below 7000 during the confinement period of the COVID-19 pandemic. Such findings imply that the pandemic further exacerbated the ever-increasing prevalence of low-level physical activity [60,61], emphasizing the necessity of adopting appropriate measures to reverse this trend. Furthermore, this meta-analysis focused on observational studies based on monitoring devices. Since monitoring devices may encourage users to engage in physical activities [6], the number of daily steps during the confinement period might have been even lower in the population than was currently observed in the samples. In addition, the impact of COVID-19 on daily steps may persist in the long term. Although some researchers report that daily steps gradually recovered to the prepandemic level after the lifting of restriction measures [49,62], more studies argue that worldwide daily steps remain depressed compared with the prepandemic level (ie, the immediate 2 years before the outbreak of COVID-19) [59,[63][64][65][66]. Thus, the consequences of long-term physical inactivity, which may be further exacerbated, should be addressed.

Comparison With Previous Work
Our finding of a reduction in daily steps during the confinement period of the pandemic is consistent with findings from previous studies using different physical activity metrics [67,68]. An earlier meta-analysis found that sedentary time significantly increased, by 126.9 minutes per day in adults and by 46.9 minutes per day in the elderly, during the confinement period of the pandemic [67]. Another systematic review reported that most of the included studies revealed a decrease in physical activity in most participants [68]. All studies showed an increased sedentary time in healthy adults and those with medical conditions during the lockdown period [68]. According to this evidence, public health messages about staying active during the pandemic appear to have had little effect on the population's engagement in physical activity [69]. In addition, 2 studies explored gender differences in the change in physical activity during the COVID-19 pandemic but had inconsistent conclusions [24,25]. One study found that men had more clearly decreased moderate-vigorous physical activity and increased sedentary behaviors than women during the pandemic [24]. However, another study failed to show significant differences between men and women in self-reported decline in physical activity [25]. Our meta-analysis adopted a primary indicator of physical activity, ie, daily steps, and found that daily steps declined substantially during the COVID-19 confinement period. Such a decline varied by region but not by gender. These results are consistent with previous studies [24,25,67,68].
Based on data collected from 187 countries and districts by a smartphone app, Tison and colleagues [59] found that mean daily steps declined by 5.5% (287 steps) within 10 days of the pandemic declaration by the World Health Organization and by 27.3% (1432 steps) within 30 days. The authors also reported noticeable differences across regions; for example, Italy, France, Brazil, and Iran exhibited a more than 40% maximum decrease, while Sweden exhibited a maximum reduction of daily steps of less than 10% [59]. Furthermore, regional differences were significant. For example, several studies showed that the decline in daily steps during confinement varied considerably among Chinese adults from different provinces [40,41,43]. One nationwide study in Japan found that daily steps declined significantly after the declaration of a state of emergency in urban areas but not rural areas [62].

Limitations
Several limitations should be acknowledged. First, daily step data are lacking from Africa and South America, limiting the generalizability of our findings. Second, when comparing regional differences across countries, we could not rule out potential sampling bias, because most of the included studies lacked sufficient nationwide representativeness. Therefore, future studies are needed to verify our findings. Third, since long-term data from the period that confinement was lifted are not suitable for inclusion in a meta-analysis, we could not directly assess the long-term impact of COVID-19 on physical activity levels using meta-analysis techniques. As more published data become available [59,[63][64][65][66], this will be an important direction for future studies. Fourth, we did not examine the impact of reduced daily steps on health outcomes, owing to a lack of relevant data. Future studies are expected to address this crucial issue. Finally, there was considerable study heterogeneity. Potential explanations include discrepancies in confinement measures across countries or districts and in the adherence to policy of residents, as well as unclear or different time frames over which the average daily steps were calculated, the possibility that monitoring devices were changed in the different reporting periods, and different durations of observation.

Conclusion
In summary, we found that daily steps declined substantially during the COVID-19 confinement period. Our findings indicate that COVID-19 further exacerbated the ever-increasing prevalence of low levels of physical activity, emphasizing the necessity of adopting appropriate measures to reverse this trend. Further research is required to monitor the consequence of long-term physical inactivity.