The COVID-19 epidemic has made access to a healthy lifestyle difficult/challenging because of limited opportunities for individuals to go out and play outside. The new lifestyle that has been adopted in response to COVID-19 is becoming entrenched and is likely to continue for a long time, changing the nature of individuals’ employment and lifestyle. One factor contributing to the negative impact on mental health common to each life stage due to such lifestyles is the “decline in physical activity level”. In this special issue, four experts who are actively conducting research on physical activity, sedentary behavior, and mental health issues in the context of the changes in work and lifestyles that are expected to continue will discuss the actual conditions and relationships among these issues, as well as how they can be resolved and their effects on the mental health of children, adults, and the elderly. They provided content that led to specific solutions for each life stage. With the anticipated long-term effects of the pandemic-related lifestyle, the information provided in this special issue will be useful in addressing and solving issues and problems in the fields of stress science and public health.

In this paper, we report on how the prolonged COVID-19 pandemic affected children and adolescents’ physical activity and mental health. Previous studies in PubMed revealed that only one of the 107 studies currently reported the impact of the prolonged. Therefore, a web-based questionnaire survey was conducted in Japan on February 10, 2022. A total of 236 adults (84 males and 152 females) responded to the electronic survey. Participants with children in the elementary school reported that their opportunities for exercise had decreased (100%), while 11% of participants with children in middle school or high school reported that they thought their opportunities had increased considerably. As for stress, 100% of participants with middle school or older children reported feeling it. In the KH Coder analysis of the free text, elementary school children seemed concerned about adjusting to life changes such as being silent about school lunches. On the other hand, junior high school and high school students were found to be adapting to the life changes caused by the COVID-19 but were also facing increased stress and new infection risks. It is necessary to divide the support for children and adolescents in prolonged COVID-19 pandemic according to their age.

Sedentary behavior is defined as any waking behavior involving an energy expenditure of 1.5 metabolic equivalents or less while in a sitting or reclining posture. Such behavior is particularly prevalent and has increased during the COVID-19 pandemic. Sedentary behavior has been associated with morbidity and mortality from various non-communicable diseases, even independent of physical inactivity. In addition, sedentary behavior is associated with an increase in the risk of mental disorders. We conducted a 1-year prospective cohort study among 233 Japanese workers without major depressive episode (MDE) and included 231 workers in the analysis. The estimated median posterior probability distribution of the HR of long sitting time was 2.11 (95% highest density interval [HDI]: 0.42-10.22) after adjustment for physical activity level and other covariates. However, the linear association indicated conflicting results. Non-linear associations between sitting time and MDE onset might explain this inconsistency. The evidence for an adverse association between sitting time at work and MDE onset remains inconclusive. Future studies with larger cohorts and greater statistical power should be conducted to confirm this association.

Physical restrictions during the COVID-19 pandemic raised health consequences among older adults. The amount of physical activity decreased because of the pandemic, which may lead to a higher incidence of frailty. However, several older adults changed their physical activities positively during the pandemic. The relationship between physical activity and mental health among older adults was maintained even during the pandemic. Those who performed greater levels of physical activity showed higher levels of mental health. Since these kinds of studies are cross-sectional and maybe recall biased, longitudinal studies are needed. So, we focused on exercise as a coping strategy to maintain physical and mental health during the COVID-19-related stay-at-home period and examined its impact on mental health using longitudinal data. About 80% of participants engaged in either walking or exercise at home as a coping strategy. Although the mental health of older adults declined greater than the normal annual change, those who engaged in walking maintained better mental health than those who did not. Therefore, it is necessary to actively encourage physical activity and exercise for older adults to stay healthy and cope with stress during the COVID-19 pandemic.

This study reviewed previous studies and discussed the relationship between sedentary behaviour and mental health in older adults. We also discussed the impact of the COVID-19 pandemic on sedentary behaviour and mental health in older people. The findings suggest that longer sedentary time may have a negative impact on mental health. Especially, previous studies consistently reported that mentally-passive sedentary behaviour, such as television viewing, is associated with poorer mental health in older adults. The COVID-19 pandemic has affected people of all ages, including the older population, by decreasing their physical activity and increasing their sedentary time. These changes in activity have led to deterioration in mental health. Therefore, it is essential to send public health messages to people encouraging them to reduce sedentary time in their daily lives and be physically active to maintain and improve their health, including their mental health, even in the COVID-19 pandemic. It is crucial to reduce mentally-passive sedentary behaviour, such as television viewing, to maintain mental health in older people.

This study investigated the relationships between reappraisal sub-strategies and affects, controlling for the intensity of emotion. The participants were 150 undergraduate and graduate students. They were instructed to recall a recent most stressful event and were asked to answer a questionnaire measuring reappraisal sub-strategies, depression and anxiety, active pleasantness, and inactive pleasantness. The results showed that “change current circumstances” was negatively related to depression and anxiety, while “explicitly positive” was positively related to it. In addition, “change current circumstances” and “technical-analytic-problem solving” were positively related to active pleasantness, while “change current circumstances,” “physical or psychological distancing,” and “acceptance” were positively related to inactive pleasantness.

This study aimed to examine the effect of the tendency to avoid hurting friends on trust during adolescence. A questionnaire survey was conducted on 286 university students (95 males and 188 females and 3 unknown, whose mean age was 20.04 ± 1.45 years) using two scales. “The tendency to avoid hurting each other” scale consisted of three factors, namely “avoidance of hurting friends and courtesy,” “ensuring distance,” and “avoidance of being hurt by friends;” and the “students’ trust in schoolmate” scale consisted of two factors, namely “trust in friends” and “distrust in friends”. Pass analysis showed that “avoidance of hurting friends and courtesy” had a positive effect on “trust in friends,” while “ensuring distance” had a negative effect on “trust in friends.” This suggests that the tendency to avoid hurting friends is an adaptive behavior, which can increase trust and decrease distrust in friends. Furthermore, “avoidance of being hurt by friends” had a positive effect on “distrust in friends,” while “avoidance of hurting friends and courtesy” had a negative effect on “distrust in friends.” In the future, it is necessary to examine the relationship between the tendency to avoid hurting friends and adaptive indicators such as mental health.