This study developed an mSMI for highly stressed workers and evaluated its effects. We found that mSMI effectively reduced perceived stress. This is consistent with previous findings that a mobile app-based stress management program (called Mind Healer) for nurses  and a mindfulness-based mHealth intervention for health care workers during the COVID-19 pandemic reduced perceived stress .
However, we found a small effect size of mSMI on perceived stress. A recent meta-review of seven meta-analyses on mobile app mental health interventions reported a small to medium effect size of mobile apps for stress management . Contrastingly, a mobile application administered for 4 weeks to nurses had a high effect size on perceived stress . Our observed small effect size could be attributed to the inadequate treatment dose. We instructed participants to use the mSMI for at least 10 minutes per session twice a week for 6 weeks. However, our logs showed that the participants accessed the app for an average of 10.4 minutes per week. Since we used a self-guided intervention, we delivered information regarding how-to instructions for each feature and personal information processing through the FAQ page and SMS. Additionally, we answered participants’ questions through a chat channel. Nevertheless, the participants did not adequately use the interventions. In the post-intervention satisfaction survey, participants mentioned that the periodic reminder text messages were stressful for them. There didn’t reinforce program engagement. Facilitating program engagement requires an approach that includes enhancing participants’ initial motivation, frequent and effective reminders, education on the importance of active participation, and financial and verbal incentives .
Also, as in the method of this study, the limitation of non-face-to-face interventions could have contributed to the failure to induce marked stress relief. A study  that administered a 6-week resilience training to health care workers with work-related stress reported that a smartphone-delivered intervention only improved well-being. Contrastingly, an in-person intervention reduced stress and emotional burnout as well as promoted well-being. Therefore, one or two face-to-face coaching sessions should be included to boost the effectiveness of mHealth interventions. If in-person interventions are not possible due to factors, including the recent COVID-19 pandemic, video conferences (e.g., Zoom, Meet, Teams, and Webex) should be conducted at the participants’ convenience to emphasize the importance of self-management and encourage steady participation.
In our study, mSMI was not effective for anxiety, depression, and work engagement. This is consistent with a previous report that a 4-week stress-management intervention for nurses using a mobile app did not significantly mitigate depression, anxiety, and emotional labor . However, meta analyses presented [26, 28] that mobile-app interventions significantly improved on depressive or anxiety symptoms with medium effect size. In particular, a 3-week intervention to reduce stress for university students using a cognitive behavioral therapy-based mobile app (called Feel Stress Free) changed anxiety and depression symptoms . The eHealth stress management for employee has already improved anxiety , insomnia [8, 9], burnout [8, 9], work engagement , and work experience . Digital interventions improved work and social functions as well as reduced depression and anxiety . Future studies on mHealth intervention should examine changes in mental health symptoms or job-related outcomes among workers. Anxiety and depression increase by 2.15 and 1.87 times, respectively, among manufacturing workers working >60 hours a week . Therefore, there is a need for intervention studies to examine mental health symptoms with respect to extended work hours.
In our study, participants were generally satisfied with the app; however, they suggested several improvements, including incorporating the latest IT such as automatic stress measurement using a sensor or voice control features. User acceptability and adherence rates are especially critical for mobile interventions . Specifically, emotionally relaxed, warm, and appealing designs should be applied to boost users’ adherence rates to ensure effective prevention and treatment of mental health conditions. Therefore, there is a need for customized mobile apps tailored to specific target populations by incorporating the latest technology to apps promoting mental health management.
This study has some limitations. First, the treatment dose was lower than planned, which could have compromised the internal validity. Second, the study was conducted during the COVID-19 pandemic; therefore, external factors, including COVID-19-related depression, may have influenced the intervention outcomes. However, this study is significant since we administered an individualized mHealth intervention on highly stressed workers for preventing mental health problems.