Aims: Paying attention to factors affecting mental health in military forces can control mental disorders, maintain the health of employees, and increase their efficiency. This study aimed to investigate the predictive role of physical activity on reactivity to perceived stress and mental toughness of male police officers.
MATERIALS & METHODS
The present research method is descriptive-correlation type. The statistical population of this research was made up of all male police employees in Yazd City in 2022 in Iran, of which 174 people were selected as a statistical sample using the available method. The criteria for entering the research were not taking psychiatric drugs, not having severe physical disorders, and completing the informed consent form in the research, and the criteria for exiting the research were unwillingness to fill in the questionnaires. The tools used in this research were Sharkey's physical activity questionnaires, Clough's mental toughness (MTQ48), and Shultz et al.'s perceived stress reactivity scale (PSRS).
Sharkey's physical activity questionnaire: To determine the level of physical activity, Sharkey's standard physical activity level questionnaire [19] was used. The mentioned questionnaire has five questions and each question has five options and it was prepared and compiled based on the Likert scale. Each question is given a minimum of 1 and a maximum of 5 points; Therefore, the total score of each person from the questionnaire is between 5 and 25. The validity of the questionnaire in the military forces has been confirmed by Shah Hosseini et al and its reliability has been reported with Cronbach's alpha method of 0.72 [20]. In the present study, the reliability of the tool was obtained using Cronbach's alpha coefficient of 0.79.
Clough's Mental toughness Questionnaire (MTQ48): The 48-question mental toughness questionnaire was designed by Clough et al. in 2002 and has six subscales: challenge, commitment, emotional control, life control, self-confidence in abilities, and interpersonal confidence. Answers to each question are evaluated on a five-point Likert scale ranging from 1 (completely disagree) to 5 (completely agree). The scoring of some questionnaire questions is reversed. The reliability coefficient was obtained by the test-retest method by Clough, 0.9 [21]. In the country, the validity of the verification questionnaire and the reliability of the entire questionnaire and its components using Cronbach's alpha method have been reported from 0.77 to 0.93 [22]. In the present study, the reliability of the tool was obtained using Cronbach's alpha coefficient of 0.86.
Shultz et al.'s Perceived Stress Responsiveness Scale Questionnaire (PSRS): Shultz et al. [7] have developed the Perceived Stress Responsiveness Scale to test the individual differences of subjects in the pattern of responding to stressful experiences. The PSRS is a self-report questionnaire that assesses typical mental reactions to various stressful situations at multiple levels. This questionnaire has 23 questions, 5 long reactivity subscales, reactivity to work overload, reactivity to social conflicts, reactivity to failure, reactivity to evaluation, and a general component. This test is used to test individual differences in responding to stressful experiences. Participants answer each question on a three-point scale. In this questionnaire, some items are scored inversely. Cronbach's alpha coefficient of the questionnaire was reported by Shultz et al between 0.70 and 0.80 [23]. The validity of the questionnaire has been reported by Shokri et al., and the reliability of the entire questionnaire and its components using internal consistency coefficients from 0.75 to 0.90 [24]. The reliability of the entire questionnaire in the present study was obtained using Cronbach's alpha coefficient of 0.78.
After coordination with the officials of the relevant military center, the researchers attended to distribute and collect the questionnaires among all the employees at the place of implementation in the morning and administrative places. In the first stage, after explaining the research and how to complete the questionnaires, the participants were invited to participate in the research. Then, after obtaining the consent of the participants, according to the criteria for entering and exiting the research, each of the employees was asked to complete the informed consent form to participate in the research, personal information, and questionnaire items without entering their names and assured them. All information will remain confidential. Also, to avoid the bias of the answers among the respondents, they were informed that the results of the research did not affect their career process and there is no right or wrong answer to the questions in the questionnaire.
Ethical Permissions: This research is taken from the thesis of the first author at Yazd University. Before the implementation of the research, the necessary arrangements were made with the officials of the police command of Yazd city, and the said plan after initial evaluations and proposal writing in the research commission of Yazd University with code of ethics https://ethics.research.ac.ir/IR.YAZD.REC. 1401.086 was approved. In addition, before conducting the research, the consent of the research subjects was obtained and they were assured that the information would be confidential.
Statistical Analysis: The research data were analyzed with descriptive statistics, Pearson's correlation coefficient test, linear regression, and using SPSS 25 software. In all statistical tests, the significance level of α=0.05 was considered.

FINDINGS
The average age and work experience of the participants were 35.87±8.37 years and 14.24±7.57 years, respectively. Also, the mean scores of physical activity variables were 13.17±4.55, reactivity to stress 22.05±7.63, and mental toughness 155.12±19.70. The results showed that the prerequisites for performing the Pearson correlation and linear regression tests were in place. The assumption of normality of data distribution using the Kolmogorov-Smirnov test (p > 0.05), the assumption of a linear relationship between the predictor and criterion variables according to the distribution diagram of the variables (indicating the existence of a linear relationship between the predictor and criterion variables) and the assumption of independence of the residuals with Using the Durbin-Watson statistic was confirmed with a value of 2.01. There was a significant relationship between physical activity and reactivity to stress (p<0.01; r=-0.343) and between physical activity and mental toughness (p<0.01; r=0.336) (Table 1). Approximately 12% of the variance of stress reactivity was predicted by physical activity level (Table 2). Physical activity with a beta of -0.343 (p<0.01; t=-4.78) negatively and significantly had the power to predict reactivity to stress in military forces. Also, approximately 11% of the variance in mental toughness could be predicted based on the level of physical activity (Table 3). Physical activity with a beta of 0.336 (p<0.01, t=4.674) had a positive and significant power to predict the mental toughness of military forces.
DISCUSSION
This research aimed to investigate the predictive role of physical activity in reactivity to stress and the psychological strength of police employees. The findings showed that physical activity scores could significantly predict both variables of reactivity to stress and mental toughness in male police officers. As mentioned, military personnel always need good psychological preparation in terms of stress and psychological pressure resulting from high-risk and unpredictable activities so that they do not face problems when facing the risks of any operation and the role of exercise and physical activity as an important and influential source in physical, psychological, cognitive and social health has been proven in numerous types of research [14, 15, 25]. According to the results of the research, physical activity could explain 12% of the variance of reactivity to perceived stress. The findings are consistent with the research results of Messerli et al. [9]. In explaining their findings, Messerli et al stated that acute and chronic physical activity levels make the HPA axis more compatible with acute stress in healthy children and show lower cortisol levels. However, the results of this study are inconsistent with the results of Mücke et al. [10] regarding the relationship between physical activity and reactivity to psychological stress. Among the reasons for inconsistency, we can mention the type of research sample and the tools used. Although the mechanisms affecting stress through the implementation of physical activity are still not well known, scientific evidence has revealed the role of serotonergic, noradrenergic, and histaminergic systems in the beneficial effects of physical activity on stress control [26]. Physical activity can improve the body and deals with stress in different ways, including the effect on the level of neurotransmitters and stress hormones through the effect on the hypothalamus, pituitary and adrenal glands, etc., due to the delay in hormonal responses. Also, physical activity diverts a person's attention from threatening situations, and creating positive beliefs and expectations about the consequences of participating in physical activity, and provides the basis for increasing the feeling of self-efficacy and efficiency, which can reduce stress [25, 26].
In general, researchers believe that physical activities are related to increasing the adaptability of neuropsychological systems and changing regulatory hormones related to body immunity and creating a physiological and hormonal adaptation, including cortisol or changing the activities of leukocytes [27]. As a result of repeating the exercise, there are stable changes in the activity of the HPA axis (stress axis), which enables people to cope better with the acute experience of stress by modulating the negative consequences of stress-causing stimuli, and this creates a balanced mental and psychological condition [ 27, 28]. Exercise appears to reduce stress reactivity by decreasing vascular resistance, norepinephrine, and HPA axis responses, in addition to increased plasma volume, cardiopulmonary baroreceptor sensitivity, increasing β2 mediated vasodilation, and endorphin levels. [29]. According to the stress mutual adaptation hypothesis, the activity of the HPA axis and sympathetic adrenal medullary (SAM) during physical stress, and regular physical activity can be generalized to other cases. Higher levels of physical activity, regular exercise, and better fitness are also associated with lower reactivity to psychosocial stressors, which in turn are associated with better health outcomes [10, 29].
New experimental research has concluded that physical activity in response to psychosocial stress reduces stress reactivity in men and women. While most studies have examined long-term stress or laboratory-induced cognitive stress, the reasons for how physical fitness may influence acute operational stress responses are less well understood [8]. In a related study, Throne et al. investigated the effectiveness of exercise training on the stress reactivity of firefighters using a computer-simulated fire scene as a stressor and showed significant effects of physical exercise compared to the control group [30]. It seems that the findings of the present study are due to the argument that participating in physical activity regularly due to the release of endorphins gives people the opportunity to reduce anxiety and confusion in dealing with stressful situations and better identify the source of stress and use a more efficient way to deal with stressful situations. In other words, people with physical activity deal with the existing stress by focusing on solving the problem to solve the problem and then relieve the stress caused by it. The results of this research also showed the ability to explain 11% of the variance of the mental toughness variable by the physical activity variable. The results are consistent with the research of Xu et al. [15], however, they are somewhat inconsistent with the results of Dumčienė [31], which can be pointed to the type and sample of the research. In line with these findings, researchers have shown that exercise and physical activity cause biochemical balance of the brain and body. Probably, one of the theoretical models of psychosocial changes related to exercise (relief or relaxation), activation of the central nervous system, and endorphin release [32]. Also, GABA-aminobutyric acid, as a neurotransmitter that plays an important role in controlling nervous and mental impulses, is better regulated by sports activities, which calms the brain and increases a person's self-control to some extent [25, 28, 32]. Researchers have stated that higher levels of mental toughness are associated with lower levels of perceived stress and higher levels of emotional control. Also, mentally tough people see stress as a challenge, have more effective coping strategies in facing stressful situations, and are committed to achieving their goals and dealing with the stressful factor [33]. As mentioned, mental toughness is related to mental health and as a source of internal resistance, it reduces the negative effects of stress and prevents the occurrence of mental disorders. It seems that performing physical activities can create a platform and strengthen mental toughness and provide the basis for the emergence of talents and a better understanding of people's abilities [34].
In general, many studies have shown that high self-esteem is associated with higher self-control. When a person has a negative view and negative thoughts and self-control, instead of trying to get out of the vicious cycle, he will give in to situations, which causes self-loathing and will lead to the strengthening of more negative structures of control in the mind. Therefore, it can be concluded that physical activity by promoting self-control increases self-monitoring, planning, and emotional regulation and helps people to have a clearer view of the future [25, 28]. There is also an explanation that active people benefit from more self-awareness and have more power to control their soul and spirit because physical activity is an important factor in improving psychological variables such as mental toughness and can give a person more control power to manage emotions and cause daily physical stress. This causes control over the behavior and actions of the soldiers, and as a result, they do not make hasty decisions in the face of challenging military job situations and missions. It can be concluded that physical activity successfully manages and controls the emotions caused by military occupation. The relationship between mental toughness and physical fitness and stress has been shown in some research, including the research of Sandvik et al. [8]. They stated that mental toughness and physical fitness may be important factors in how operational stress affects the police environment, and it seems that people who have high toughness and good physical shape are better able to recover after a stressful incident. The statistical sample of the present study included male employees of Yazd City, and caution should be taken in generalizing their data to others. Also, the uniqueness of data collection by questionnaire and self-report and the use of available sampling methods were other limitations of this research. Considering the relatively limited research records in the military, it is suggested that in future studies, in addition to controlling these limitations, other psychological factors related to physical activity should be investigated.
Conclusion: Based on the results, the physical activity level of police male employees can predict their reactivity to stress and their mental toughness.
Clinical & Practical Tips in POLICE MEDICINE: Considering the results of the research and the fact that due to the nature of their work, police personnel are exposed to acute and chronic stressors to a large extent and as a result the risk of mental disorders, it is suggested that those involved in military sports should make appropriate plans for the active presence of respected military personnel. They should be used in regular physical activities to reduce reactivity to stress and increase mental toughness and thus increase mental health to optimally perform assigned tasks and increase their efficiency.
Acknowledgments: We hereby express our sincere thanks to all the respected officials and dear military personnel who cooperated in the present research.
Conflict of interest: The authors of the article stated that there is no conflict of interest regarding the present study.
Authors' Contribution: First author, data collection; second author, idea presentation, study design; third author, study design; Fourth author, data analysis; All authors participated in writing the article and revising, and all accept responsibility for the accuracy and correctness of the content in the article by finalizing the article.
Financial Sources: This research had no financial support.

Matrix of correlation coefficients between research variablesTable 1)