Work-related stress can be defined as the harmful physical and emotional responses that occur when the requirements of the job do not match the capabilities, resources, or needs of the worker [1]. In the case of individual workers, work-relate distress can cause job dissatisfaction, absenteeism, accidents, voluntary unemployment, and finally lead to a decreased quality of life [2]. For employers, work-related stress has a significant effect on the risk of worker's being injured in an occupational accident, which increases costs and lost productivity, and finally leads to a deterioration of management [3]. From the perspective of the nation and the community, these results have negative impacts such as competitive decline [4]. All workers can suffer from work-related stress, which has a huge social cost. Thus, work-related stress is not only an individual risk factor, but also a risk factor for employers, the community, and the country's development.

In 27 countries of the European Union (EU) in 2005, 22.3% of the workers had symptoms caused by stress [5]. In the United Kingdom, estimates of work-related stress was 428,000 cases (40%) out of all work-related illnesses. This could be a factor responsible for the high number of lost work days, which reached 10.4 million in 2011/12 based on the Labour Force Survey data [6]. In a study conducted in Korea, 346 workers (22%) among 6,977 experienced critical levels of stress [7]; this was widely reported, particularly in small and mediumsized enterprises. Male white-collar workers with high job stress suffered from more depression, anxiety, and stress symptoms than workers with low job stress in an automobile company [8]. Depressive symptoms of male workers had a greater impact on work-related stress than the quality of sleep and fatigue in the case of a small manufacturing company [9]. The self-perceived fatigue of white-collar male workers had a greater impact on work-related stress than the psychosocial factors in the case of small and mediumsized enterprises [10].

In order to manage work-related stress, effective interventions applicable to the workplace are required. Internationally, various stress interventions in the workplace have been conducted on the basis of work-related stress research. Depending on whether the intervention focuses on an individual's psychological resources (individual level) or occupational context (organizational level), there are two different approaches to managing work-related stress. At the individual level, relaxation and, cognitive-behavioral techniques have been applied to improve an individual's psychological resources and responses. At the organizational level, job adjustment and workplace communication activation have been applied to improve the occupational context. In previous intervention studies at only the organization level, there was little impact on individual variables. Individual level interventions had more influence on psychosocial, physiological, and organisational aspects [11]. In a meta-analysis of workplace stress interventions, the cognitive-behavioral approach was found to be the most effective technique [12,13]. One year after the individual intervention, biofeedback and muscle relaxation showed reduced absenteeism. In the following year, however, the effects of the intervention disappeared and the variables returned to their previous status [14]. In a similar study, individual level interventions showed only short-term effects [15]. Secondary or tertiary prevention, which was usually applied to the individual level intervention, strengthened coping with stress that had already occurred, but primary prevention, which was usually applied as an organizational level intervention, reduced the cause of stress. Therefore, only secondary or tertiary prevention without primary prevention seemed to have a limited effect on the reduction of work-related stress. In previous reports, both individual and organizational management for improving workplace mental health were important to manage the causes of stress in the workplace [12]. The improvement of the psychosocial work environment is helpful to the improvement of the mental health of workers [16], and mental health is closely related to productivity improvement [17]. If intervention measures are not mutually exclusive but complementary, an even greater effect can be observed. Therefore, comprehensive stress management should be emphasized [18].

Participation in workplace health promotion has increased significantly [19,20]. Involvement of the participants can enhance autonomy, justice, and social support, which are the basic components of work-related stress [21]. Participatory action-oriented training (PAOT) is one of the methods for engaging employees in workplace interventions. Workers who participate in this workshop discover the problems caused by their own work environment. The program suggests appropriate solutions to workplace problems and improves the work environment [20]. This participatory approach to reducing work-related stress in the work environment reduces psychosocial stressors. It also reinforces the buffer elements against stress [22]. The application of both participatory approach methods and psychosocial stress reduction methods has been effective in improving a worker's mental health and productivity [23].

In this study, a comprehensive stress management program was applied to a medium-sized enterprise that experienced an increase in work-related stress due to rapid growth. The comprehensive stress management program was composed of both participatory organizational intervention for improving the work environment and individual interventions for reinforcing the coping skills against stress. Further, we implemented the stress management program and evaluated its effects.

The comprehensive stress management program, which was composed of the organizational and the individual level intervention, was conducted to reduce work-related stress in a medium-sized enterprise. Work-related stress management has usually been focused on individual management corresponding to secondary and tertiary prevention [12]. Thus, the occupational context including physical, environmental factors that caused stress tended to be overlooked. By changing the demands of the work environment and emphasizing organizational support and responsibility, the comprehensive stress management which encompasses primary, secondary and tertiary prevention is emerging as important [18,30-32].

To reduce work-related stress, workers carried out a risk assessment of their workplace and created ready-to-run action plans by participating in a PAOT. The PAOT using the MHACL has shown a reduction in work-related stress in previous studies, similar to our findings. In a manufacturing company, female white-collar workers showed improvement in job skills, mutual support, and psychological stress [33]. In an electronic components factory, blue-collar workers exhibited an improvement in mental health and job skills [34].

The MHACL helped the participants to efficiently discuss issues related to the reduction of work-related stress through improvements in the work environment. The MHACL encompasses a variety of areas from the physical to psychosocial work environment; therefore, it can be applied to various types of workplaces [28]. In this study, the MHACL was applied to establish and implement action plans in each team. Based on the practices to be improved as determined through a discussion, each team prepared three short-term and long-term action plans. In previous studies, the MHACL was useful guidance for work-related risks and facilitated workers to set immediate goals and to plan local feasible improvements activities [20,35]. In this study, the examples of improvement activities were as follows: spraying water in order to prevent dust, adjusting work hours considering individual circumstances, and arranging regular meetings to share information. Improvement plans were made to remove obstacles causing work-related stress. Plans were made to be feasible, and improvements have been made in the desirable direction.

A comparison of KOSS scores obtained through pre- and post-stress surveys was used for evaluating the intervention effect. Blue-collar workers exhibited significant effects in the case of the subscales for the physical environment, job demands, organizational system, lack of rewards, and organizational climate. Work-related stress was reduced in the process of discovering the practices to be improved, discussing action plans with team members, and implementing improvement activities. In a previous study on the development of action plans by workers for resolving problems in the workplace, desired effects were also shown through a process of recognition and intervention [36]. In order to reduce workplace stressors and improve business efficiency and productivity, an agreement among various departments with respect to preparation for unexpected work and an understanding of task progress should be reached. White-collar workers exhibited significant effects in the case of organizational climate. Although not statistically significant, the subscales of job demands, insufficient job control, interpersonal conflicts, organizational system, and lack of rewards were improved. In the case of white-collar workers, work-related stress was induced by unreasonable communication and relationship conflicts. They felt the burden of close deadlines, work interruption due to other work, increased workload, and excessive responsibility. Work-related stress was reduced after carrying out the suggested improvements. These results were similar to those of training programs on social motivation and interpersonal conflict mediation [37]. A comparison of WSRI scores obtained through the pre- and post-stress surveys was used for evaluating the intervention effect. Although not statistically significant, the subscales of somatic symptoms, depressive symptoms, and work-related symptoms were improved. In a previous workplace-based participative intervention study, there was significant reduction in sleeping problems in hospital workers. Although not statistically significant, psychological distress, which includes anxiety, depression, aggressiveness, and cognitive problems, was also reduced after an intervention, as found in our study [39].

In the case of workplace health promotion, it is essential to promote voluntary initiatives and participation of workers throughout the entire intervention process: planning, implementation, and review [20]. In various sectors, the participatory approach has been proven to be effective in workplace stress management [33,34,38,39]. Encouragement and active participation of employees in risk assessment and control could be incorporated into the management system, followed by facilitating organizational change. In our study, most of the employees participated in the organizational level intervention. During workshops, inter- and intra-departmental communication was activated, and this effect was sustained throughout the execution of the improvement activities. Good communication helped to alleviate the problems caused by work-related stressors such as interpersonal conflicts, adverse effects to the organizational system, and deterioration of the organizational climate. These achievements would be impossible without good communication and cooperation among the departments. Assuming that the entire company was one organism made of a number of departments, it was not sufficient to enhance the individual's coping resources with a random selection for dealing with stressors that occurred in a relationship between departments or in an organizational context. Thus, primary prevention that emphasizes worker participation has attracted attention [18].

Individual level intervention included personal interviews and the dissemination of stress management information. The interviews began with a discussion of the interviewees' own work-related stressors and stress responses, and enhanced or supported their coping strategies against stress. Before the interview, the interviewer checked the good practices and practices to be improved for the department to which the interviewee belonged, through a team-based participatory workshop. This information helped the interviewer and the interviewee to communicate efficiently about stressors and coping methods. In addition, sensitive organizational level stressors that were difficult to describe in a public workshop were revealed in the personal interview, and feedback could be provided through improvement activity checks or SIC contest.

As this study did not apply blinding, a possible Hawthorne effect could have produced the favorable results, as workers already knew they were under the intervention. Further, this study did not include a control group; therefore, the interpretation of the results is limited. However, considering the characteristics of the workplace intervention study, the control group in the same workplace was likely to be affected by the intervention group, and the intervention effect could thereby decrease. In addition, a number of previous studies have already proven the effects of work-related stress interventions; thus, the need to select a control group is relatively low. In this study, the stress surveys relied on self-reported questionnaires; hence, an information bias could have originated from the subjective tendency to remember work-related stress. The KOSS and WSRI, as domestic evaluation scales, have certain limitations as compared to international evaluation scales. However, they provide a national reference level and have proven reliability to make an accurate assessment. Our study evaluated only the short-term effects of a comprehensive stress management program; a continuous assessment is required.

Despite these limitations, this study has great significance in terms of workplace stress intervention considering that previous stress studies in the workplace were confined to epidemiological observation in Korea. The comprehensive stress management program was conducted on the basis of stress surveys. Both organizational level interventions through participatory improvement activities and individual level interventions through interviews and information dissemination were performed. This study suggests that a comprehensive stress management program can improve the mental health of workers.

Authors declare that they have no competing interests.

SAK, CS, MHP, JTL, KHW, and HJ conceived of the study and participated its design. MHP, CS, KHW, KK, and HJ participated in the intervention and the acquisition of data. SAK, CS, KK, CKL, BCS, JHK, and JTL performed the statistical analysis and interpretation. SAK and MHP drafted and revised the manuscript. CS coordinated the study and helped to draft and revise the manuscript. All authors read and approved the final manuscript.