*2.1. Design*

While conceptualizing the author's own research, the biopsychosocial model of health was used [8–10]. Based on the above theoretical frameworks, in the quasi-experimental model, a cross-sectional research plan was designed.

In line with the adopted theoretical approach, in this research project, variables of biological (gender), psychological (physical activity, mental health disorders, cognitive disorders) and social (social functioning) factors were distinguished, which were assumed to interact with each other.

Whereas the prognostic factors of mental health and cognitive disorders, as well as the social functioning received, may vary depending on country and even region [12,38–40], the analysis focused on the consequences of the epidemic in the population of Eastern Poland, which means that the surveyed sample included only the inhabitants of these areas. Additionally, the concept takes into account the moderating role of gender, as it is an important biological determinant of susceptibility to physical activity, mental and cognitive disorders and social functioning [11,12,14,15,41].

It was assumed that the mentioned parameters are latent variables, which is characteristic of fully interactive approaches and at the same time allows for a detailed analysis of the mutual and multifaceted interaction of individual factors creating the structure of physical activity, as well as shaping the state of mental health, cognitive processes and social functioning [8–10,42].

Given that the biopsychosocial model of health [9], as well as numerous empirical premises, suggests a significant role of sociodemographic factors for the variables analyzed in the study, during the conceptualization of the research, many controlled variables, which may potentially influence the results, have been taken into account [13,43,44]. They include: gender [14,15], age [43], place of residence [38], level of education [45], marital status, number of children [15,46], professional activity [45] and health condition of the respondents [7,47,48].

In order to minimize the influence of gender on the obtained research results, the analyzed groups were of the same size. In the case of a health condition, a procedure based on establishing its constant level was applied. Age, marital status, place of residence and professional activity were checked by designating their subranges, and, as in the case of the other above-mentioned variables, the homogeneity of the studied groups was confirmed [42].

In the first stage of the analysis, the level of physical activity, mental health disorders, cognitive disorders and social functioning of women and men during the epidemic were assessed. In the next stage, the focus was on verified gender-related occurrence and significance of the interactions and relationships between the identified variables based on the modeling of structural equations in the confirmatory version.

The research was carried out in the population of adults of Eastern Poland in the period from June, 2020 to December, 2021. In total, 579 people declared their willingness to participate, and 452 women and men met the inclusion criteria (78.7%). Before and during the study, the participants showed no symptoms suggesting a risk of SARS-CoV-2 infection and were not quarantined.

The research was conducted in accordance with the guidelines of the Helsinki Declaration and received approval from the Bioethics Committee of the Medical University of Lublin (No. KE-0254/100/2020, 28 May 2020). The persons obtained all necessary information and explanations about the project. In addition, they were informed about the confidentiality of the data provided and about the possibility of receiving feedback based on individual results. In case of doubts, they had the opportunity to obtain additional explanations.

Due to the risk of SARS-CoV-2 infection and restrictions introduced in the country, each person was contacted online. The invitation to participate in the research along with contact details (telephone number, first and last names of persons to contact) was posted on the Internet on the website of NeuroCentrum [49]. It was available from 1 June 2020 to the end of November 2021. The invitation to participate in the study was extended to adult residents of Eastern Poland according to the adopted inclusion and exclusion criteria.

These inclusion criteria were: free and informed written consent to participate in the research, age (adults), origin (inhabitants of Eastern Poland), marital status (married or partnership), employment based on an employment contract or contract of mandate, no diagnosis of COVID-19 and a lack of SARS-CoV-2 symptoms, as well as good general psychophysical health. The exclusion criterion was: failure to meet at least one of the above-mentioned inclusion criteria.

Participants were recruited by phone. Those who declared their willingness to participate in the research, and at the same time met the inclusion criteria, provided the recruiter with a telephone number and an address. They were mailed an informed consent form necessary to participate in the study, along with written information about the research and a return envelope enabling the documents to be sent back. After receiving them, the individuals were contacted by phone so a convenient date to carry out the study could be set.

The questionnaire session was carried out during individual video conferences. After acquainting respondents with the rules of completing the questionnaire items, a sheet was presented to them with individual questions, and the range of possible answers were read, and answers were marked in the appropriate place on the test. On average, the research period lasted for 20 min.
