The association between physical activity and mental health during the first year of the COVID-19 pandemic: a systematic review

Introduction The Coronavirus disease-19 (COVID-19) pandemic affected countries worldwide and has changed peoples’ lives. A reduction in physical activity and increased mental health problems were observed, mainly in the first year of the COVID-19 pandemic. Thus, this systematic review aims to examine the association between physical activity and mental health during the first year of the COVID-19 pandemic. Methods In July 2021, a search was applied to PubMed, Scopus, and Web of Science. Eligibility criteria included cross-sectional, prospective, and longitudinal study designs and studies published in English; outcomes included physical activity and mental health (e.g., depressive symptoms, anxiety, positive and negative effects, well-being). Results Thirty-one studies were included in this review. Overall, the studies suggested that higher physical activity is associated with higher well-being, quality of life as well as lower depressive symptoms, anxiety, and stress, independently of age. There was no consensus for the optimal physical activity level for mitigating negative mental symptoms, neither for the frequency nor for the type of physical activity. Women were more vulnerable to mental health changes and men were more susceptive to physical activity changes. Conclusion Physical activity has been a good and effective choice to mitigate the negative effects of the COVID-19 pandemic on mental health during the first year of the COVID-19 pandemic. Public health policies should alert for possibilities to increase physical activity during the stay-at-home order in many countries worldwide.


Background
The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a highly contagious virus that infects humans and causes coronavirus disease-19 (COVID- 19), which is currently having a damaging impact on almost all countries worldwide [1]. To bring this pandemic to an end, a large share of the world needs to be immune to the virus, and the safest way to achieve this is with a vaccine. Fortunately, in December 2020 the vaccination started in the United Kingdom [2] and is currently pursued in different countries [3]. Until November 2021, 53.3% of the world population has received at least one dose of a COVID-19 vaccine [4]. However, the number of infected people and deaths continues to grow [5]. The World Health Organization (WHO) published a weekly report and on 16th of November 2021 it was observed a increasing trend in new global weekly cases [6]. From the beginning of the pandemic, as a community mitigation strategy used to reduce the spread of COVID-19, most countries adopted the stay-at-home order as well as the stimulation of facemask wearing and hygiene habits [7,8].
As a consequence of the stay-at-home strategies, mainly during the first year of the COVID-19 pandemic, studies had reported multiple behaviour changes. Some common impacts include disturbed eating behaviours [9], changes in alcohol consumption [10], and substance use [11]. A wide range of psychological outcomes has been observed during the virus outbreak, including a reduction in well-being as well as increases in depressive and anxiety symptoms [12,13]. Considering the need for social distancing measures, the investigation of possible factors that can mitigate the negative effects of social distancing on mental health should help the promotion of intervention strategies.
Physical activity (PA) is well recognised as a key factor for the prevention and management of mental illness, including mental disorders such as depression and anxiety as well as the promotion of mental health such as well-being [14,15]. Nevertheless, globally, approximately 23% of adults and 81% of adolescents do not meet the WHO recommendations regarding PA for maintaining health [16][17][18]. This situation even worsened with the COVID-19 pandemic. Studies have demonstrated that PA declined and sedentary behaviour increased during the COVID-19 pandemic stay at home order in many countries, regardless of the subpopulation [19]. Different studies sought to investigate whether these changes in PA were associated with mental health indicators during the COVID-19 pandemic and a previous systematic review synthetised that PA is an effective strategy to face the psychological effects of the COVID-19 pandemic [20]. However, the previous review included articles published between 1 January 2019, and 15 July 2020, before the second wave of the COVID-19 pandemic. Therefore, our systematic review aimed to update those findings and clarify if PA is associated with mental health during the first full year of the COVID-19 pandemic and to analyse if PA mitigates the effects of the stay-at-home order on mental health. We aimed to explore the first year of the COVID-19 pandemic because it was the period when restrictive orders were strictest when people were strongly encouraged to comply with the stay-at-home order.

Design
This systematic review focuses on peer-reviewed journal articles on the relationship of PA to mental health during the COVID-19 pandemic published until 30 July 2021.

Data sources and searches
A systematic review protocol was registered with the PROSPERO database on the 29th of January 2021 (IDCRD42021233921). A broad search strategy was employed. Searches were conducted on the 30th of January 2021, in the following electronic databases: PubMed, Scopus, and Web of Science. The search was performed in the three databases using the terms: (physical activity OR physical inactivity OR exercise OR training OR sport* OR fitness OR physical function* OR movement behavio* OR sedentary behavio*) AND (mental health OR psychological health OR depress* OR anxiety OR psychological function* OR mental function* OR wellbeing OR well-being OR burnout OR burn-out OR fear OR fears OR worries OR worry) AND (coronavirus disease OR COVID-19 OR SARS-CoV-2 OR lockdown OR shutdown OR quarantine OR confinement OR social isolation). These terms were searched in title and abstract of scientific articles. Additionally, cross-referencing search was performed in the full-text read of potentially included articles.

Study selection
Observational studies (cross-sectional, prospective, or longitudinal) were eligible for this review. Furthermore, studies were also required to meet the following criteria: (1) assessing PA by a validated instrument, (2) assessing mental health by a validated instrument, (3) presenting an analysis on the association between PA and mental health. Studies with samples including pregnant women, chronic disease patients, athletes, COVID-19 survivors, and frail older adults were excluded. Besides, studies reporting PA as a moderate or mediated variable were also excluded. Two co-authors screened titles and abstracts to identify articles that met the inclusion criteria. Two co-authors read the articles and decided whether they should be included in the analysis or excluded. The inclusion decision was consensual and in cases of disagreement, the decision was made by mutual agreement.

Data extraction and synthesis of results
Data extraction was completed independently by one coauthor. Data extracted from all studies included study details (author, year of publication, study design, recruitment processes, and date and location of the study); participant characteristics (sex, mean age); outcome and instruments, and main findings. A table was made for articles that analysed the association between PA and mental health among adults, and another table for the analyses of the association between PA and mental health among children and adolescents.

Quality assessment
The risk of bias was assessed by two independent reviewers, using the Newcastle-Ottawa Scale (NOS) [21] which was also adapted for cross-sectional studies [22]. Therefore, we used the original scale for cohort studies and the adapted scale for the cross-sectional studies. The original scale varies between 0 and 9, while the adapted scale for cross-sectional studies varies between 0 and 10, with higher scores indicating research of better quality.

Narrative synthesis
Considering the heterogeneity of methods used for the estimation of the exposures and outcomes, it was not possible to conduct a meta-analysis. Therefore, we compared the findings across the included articles according to each outcome.

Results of the search
From the database search, 734 records were identified. After removing duplicates, the titles and abstracts of 328 articles were screened concerning the eligibility criteria, and 205 were excluded. The full texts of the remaining 1237 articles were evaluated and 92 were excluded for the following reasons: sample characteristics (n = 24), data were not analysed regarding the association between PA and mental health variables (n = 23), review studies (n = 4), no valid instruments to assess PA (n = 31) and mental health (n = 6), the study was not in the period of the COVID-19 pandemic (n = 4). Thirty-one studies were included in this review, 27 about adults and old adults and 4 about children and adolescents. The flow diagram of study search and selection was created according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [23] and is presented in Fig. 1. The mean score of quality was 5.7 ± 1.5. More details are presented in Tables 1 and 2.

The association between physical activity and mental health among adults and old adults
The details of the association between PA and mental health among adults and old adults are summarised in Table 1, 27 studies were included 51].

Participants characteristics and date of filling the questionnaires
The number of participants in the 27 included studies varied between 66 [50] and 14,715 [40] participants. Regarding sex, with exception of four studies [24,31,40,48] the majority included more women than men.

Outcomes and instruments
Concerning outcomes and instruments, 12 articles used the International Physical Activity Questionnaire (IPAQ) to assess PA and one article calculated an estimate of cardiorespiratory fitness (algorithm includes age, body composition, resting heart rate and PA) [57]. The others articles assessed PA with different instruments. Mental health included analyses of subjective well-being, sleep quality, depressive symptoms, anxiety, quality of life, psychological distress, motivation, resilience, affects (positive and negative), and health-related quality of life.

Main findings
Overall, all articles found a positive association between PA and better outcomes of mental health (e. g., depression, anxiety, well-being). Physical activity was explanatory variable for mental health [25]. Physical activity was positive associated with mental health [42,49]. Articles that observed a decrease in PA during the stay-athome order also observed a decrease in well-being [47,56], negative changes in depressive symptoms [57], and negative changes in anxiety and stress symptoms [45]. This relationship seems to be bidirectional, since participants who decrease in mental health had greater reduction in physical activity [37]. Inactive people had worse well-being, highest depression and enxiety compared with moderately active and very active participants [24,51]. Also, inactive old adults had more depressive symptoms [26]. On the other hand, participants sufficiently active reported significantly lower depression and anxiety and higher life satisfaction. Moreover, it was found that exercise intensity seems to be important. Two studies founded that depression was significantly negatively correlated with moderate-intensity PA but not vigorous and walking/light exeeercuse [36,40]. Another one found that vigorous PA better predicted depressive symptoms than moderate PA [27]. Three studies suggested that the threshold of PA should be done to fells the benefits on mental health [28,39,50]. At least 4 h of MVPA reduced by 49% odds of depressive symptoms [28], and at leas 477 METs-min/week was associated with a 33% decrease in the probability of depressive symptoms [39]. On the other hand, a non-significant association was found between PA and anxiety [35], and between PA and health-related quality of life [46]. One study found that the decrease in mental wellbeing and increase in perceived stress was not related to changes in PA [44].  Chouchou et al. 2020 [29] Cross-sectional, 400 participants (58.2% women, mean age 29.8 ± 11.5 years), recruitment by online survey between the 35th and 54th days of lockdown, Reunion Island.

6
Those reporting the highest decrease in wellbeing (4th and 3th quartiles) also reported the highest decrease in their total, moderate and intense weekly PA. Impairment in well-being was independently associated with weekly PA.
Estimated cardiorespiratory fitness (algorithm include age, body composition, resting heart rate and PA). Depressive symptoms (PHQ-9). 3 Significant but small correlation between the change in weekly physical activity minutes and the change in PHQ-9 scores. Change in total physical activity energy expenditure was significant predictor of the decrease in mental wellbeing from pre to during lockdown.

COVID-fear (FCV-19S). Nutrition (HPLP-II).
Physical Activity (IPAQ-SF). Insomnia (YSIS). Depressive symptoms (PHQ-9). Anxiety (GAD-7). 8 With lowly active physically as the referent, moderately physically was significantly associated with a lower level of depressive symptoms and anxiety symptoms while highly active physically was associated with a lower level of insomnia symptoms, depressive symptoms and anxiety symptoms.
Morres, et al. 2021 [54] Cross-sectional, 950 adolescents (mean age 14.41 Increased physical activity predicted better well-being. Days of PA per week was stronger predictor of well-being than minutes of PA per week. Both in-house and out-of-house PA were beneficial. Kang, et al. (2020) [55] Cross-sectional study, 4898 adolescents (52% girls, mean age 16.3 ± 1.3 years), online survey between March 8th and 15th, 2020, China.
Physical Activity (IPAQ). Mood states (Profile of Mood States).

6
Higher levels of PA were significantly associated with lower levels of total mood disturbance.

The association between physical activity and mental health among children and adolescents
The details of the association between PA and mental health among children and adolescents are shown in Table 2, four studies were included [52][53][54][55].

Participants characteristics and date of filling the questionnaires
The number of participants ranged between 64 and 4898 children and adolescents. More girls than boys participated in the studies. The mean ages were 11, 14, 15, and 16 years old. One study was longitudinal and presents two moments of assessment, also opting for phone or video calls to collect the data [52]. The other three studies were cross-sectional, and collected data by online surveys.

Study location
One study was from the USA [52], one from Greece [54] and the other two were from China [53,55].

Outcomes and instruments
Three studies assessed PA by the International physical activity questionnaire (IPAQ) questionnaire [53][54][55], and another one used a 24-h physical activity recall [52]. Regarding mental health, different outcomes were assessed, such as anxiety, positive and negative affect, insomnia, depressive symptoms, psychological wellbeing and mood states.

Main findings
Moderate physical activity was associated with less state anxiety [52,53]. Positive affect was not related to physical activity [52]. Higher levels of physical activity were also significantly associated with lower levels of total mood disturbance [55]. Regarding the dose of physical activity, days of physical activity per week was stronger predictor of well-being than minutes of physical activity per week [54].

Discussion
This systematic review focuses on the association between PA and mental health during the first year of the COVID-19 pandemic. In particular, we sought to answer if PA mitigates the effects of the stay-at-home order on mental health. The COVID-19 pandemic generated numerous challenges for public health, particularly the significant burden of mental health in the population [58,59]. In addition, PA has been recognized as an effective mitigation strategy for improving mental health [60]. The COVID-19 pandemic has been affecting all continents in the world, at different scales. This study analysed 31 research articles, 27 about adults and old adults and 4 about children and adolescents. The articles are mainly based on cross-sectional studies and five are longitudinal studies. In nearly all of the studies comprised in the present systematic review, investigators used online surveys as the main procedure to collect data. Overall, the studies suggested that higher PA is associated with less negative mental health symptoms, such as depression, anxiety, well-being, and fear, independently of age.
The studies observed that women showed more depressive symptoms than men [28,39,50,53,55], and this trend increases with age [24] Furthermore, individuals with a lower level of masculinity traits (not specifically females) increased risk of developing depression [36], and women experienced more generalised anxiety [41]. The reduction of PA levels may mostly influence the mental well-being of females [38,49]. Those findings are expected since the literature is consistent in signalising sex differences in most mental disorders [61]. On the whole, the prevalence rates of anxiety and depression were both higher than the rates found in previous studies before the COVID-19 pandemic [36,37,43,45,48,57], which highlights a worsening in mental health during the first year of the COVID-19 pandemic. Regarding age, younger individuals experienced significantly higher anxiety and depression, also income influenced mental health, lower-income participants present worse mental health [37].
Five articles conducted a longitudinal study. Among those studies, four enrolled adults and old adults [28,44,46,50,51] and in one the sample comprised children [52]. Among the studies that have collected measures before and after the stay-at-home order, both observed a significant reduction in PA [44,46]. Two study collected measures after the stay-at-home order and during this period physical activity mean score decreased minimally [51], and depressive symptoms increase as the weeks of isolation go [28]. Other studies also reported a reduction in self-reported PA [26,33,34,37,38,42,43,45,56,57] and increase in sedentary behaviour [25,26,34]. Individuals who reported larger decrease in MVPA pre to during COVID-19 reported relatively poorer mental health [33]. Participants whose mental health got "worse" or "much worse" had greater reductions in physical activity [37]. Also, increased levels of physical activity were associated with stronger effects on wellbeing [42]. The reduction was more pronounced in men than women [32,38,44], in vigorous PA [38], and between those with lower health-related quality of life scores before the COVID-19 pandemic [46]. The possible explanation for this sex-difference is that men are more engaged in group/community PA and sports in clubs or gyms, and those were more impacted by the COVID-19 restrictions. Also, women are more engaged in low and moderate physical activities, which can be done at home. Besides, women spent more time in housework activities. Women without changes in childcare provision reported more opportunities to be physically active [41]. The same sex-differences were observed in an Italian study [62]. Increases in PA were observed for a minority, but the majority of the respective study samples demonstrating a positive change were individuals who did not meet recommended PA guidelines before the COVID-19 pandemic [32,38]. Additional reasons could be an increase in awareness for health issues and more time to pursue PA during the stay-athome order [32]. These behaviour changes can help to maintain a more active lifestyle during the pandemic. Another study found an increase of 40% in PA in a sample that was already active before the COVID-19 pandemic [35]. PA could be used as a coping strategy to deal with the consequences of the pandemic. The place where individuals prefer to practice PA seems to be important, since active participants reported greater connectedness to nature and nature relatedness than the inactive population [35].
There was no consensus across studies for the optimal PA levels for mitigating negative mental symptoms. The more the physical activity is frequent and vigorous, the best people feel themselves [24]. Among Chinese students, 2500 METs minute/week of PA every week was the optimal dose to alleviate negative emotion [50]. On the other hand, a Spanish community sample study showed that 477 METs-minute/week was associated with a 33% decrease in the probabilities of notable depressive symptoms [39]. The difference between the values must be relativised considering the samples' characteristics. The first one concerns students with a mean age of 20 years [50], and the second one concerns a community sample with a mean age of 43.2 years for women and 40.5 years for men [39]. In addition, it is claimed that at least 3000 METsminute/week reduce the odds of depressive symptoms by 47% [39]. These studies used the IPAQ to assess PA, and according to IPAQ, to reach a minimally active category at least 600 METs minute/week is needed [63]. The American College of Sports Medicine also recommends for healthy adults aged 18-65 years at least 600 METs minute/week but did not specify the minimum dose to prevent depressive symptoms [14,64].
Studies also examined the association between PA and mental health according to PA intensity. Moderate-intensity PA (e.g., walking or jogging on a treadmill, using an elliptical trainer, cleaning house) is associated with better mental health outcomes than vigorous-intensity PA [36,40], and light-intensity PA [40]. On the other hand, vigorous-intensity PA better predicted depressive symptoms than moderate-intensity PA; also the effect size was higher for the association between vigorous-intensity PA and level of resilience compared with moderate-intensity PA [27]. One study found that performing high PA levels has no positive effect on depressive symptoms [39]. Another study explored the type of PA and showed that stretching and resistance training were associated with lower anxiety, and three types of PA (household chores, stretching, and resistance training) were associated with lower depression symptoms [48].
One study explored the association of specific types of physical exercise and mental health, and founded that home-based group entertainment exercise, rope skipping and badminton, Chinese traditional sports, video dancing and sensory-motor games present a greater reduction in mental health than others types [40].
Sedentary behaviour was observed in few studies and contradictory findings were observed. No association between sedentary time and depressive symptoms was observed [26,36]. However, other studies have shown that sedentary behaviour was associated with poorer mental health [25], well-being [32] and perceived stress [44].
Concerning the association between PA and mental health outcomes among children and adolescents, only four articles were selected. Some issues must be highlighted. This population had to face, beyond the reality that changed from the COVID-19 pandemic, the changes in the education system such as online learning became the main learning method for students and uncertainty of academic development, which probably caused more anxiety level [52,53]. Both moderate and highly active groups were significantly associated with less depressive symptoms [53] and anxiety [52,53], and only the most active adolescents reported significantly lower insomnia symptoms [53] and better mood states [55]. Days of physical activity per week was stronger predictor of well-being than minutes of physical activity per week [54].
Regarding old-age samples, the studies mentioned the particular vulnerability to changes in social circumstances, and highlight the importance of health-related quality of life [46] and levels of resilience [27] to deal with the consequences of the COVID-19 pandemic on the PA level. The stay-at-home order can cause greater distress and feelings of sadness, considered specific risk factor for depressive symptoms [34]. Mental health and physical activity decrease pre to during stay-at-home order [47]. In a group that were previously regular participants of a formal exercise program, MVPA was significantly higher within the non-depressed group compared with depressed group [26]. Being active previously of COVID-19 confinement did not prevent 30.4% of Brazilian older adults from having depressive symptoms, but these results is much lower than prevalence of depression in Brazilian general population, which is 68% [34].
The present systematic review had some limitations that must be mentioned. First, the studies present correlative analyses, not causal ones, thus randomised controlled trials must be conducted in the context of the COVID-19 pandemic and the stay-at-home order to clarify the direction of the association. However, beyond the COVID-19 context, randomised controlled trials showed that PA interventions show beneficial effects on mental health outcomes such as depression and anxiety [65]. Thus, a nuanced perspective particularly during the COVID-19 context in future research is needed. Moreover, the included studies with community samples were limited, and the analyses were mostly based on convenience samples with college students, which had specific characteristics and low mean age. Thus, future research needs to focus on representative study samples.

Conclusion
This review helps to clarify the positive association between PA and mental health during the first year of the COVID-19 pandemic, especially considering the effects of the stay-at-home order worldwide. Although there is an association between increased PA and improved mental health, further studies are needed, specifically randomised clinical trials, to identify the direction of this relationship, and what kind of PA, intensity, and frequency are most indicated to maximise the effects. Also, an investigation to examine the association during the second year of the COVID-19 pandemic is needed. The impact of the COVID-19 pandemic on mental health may be continuous and long-term [66,67]. Thus, public health agencies must provide timely and effective interventions, in which PA and exercise should be a priority.