This study first examined the 24-week app-based walking program to strengthen socio-cognitive factors in female KC middle-aged migrant workers to improve their PA adherence and prevent CVD risk. The ET group, which received an enhanced app-based walking intervention and strategies for improving exercise-related self-efficacy and social support, showed a significant reduction in 10-year CVD risk compared to the ST group at week 12, which received only the app-based walking intervention. Our study highlighted that community-based PA interventions that reinforce socio-cognitive aspects using wearable devices could effectively prevent CVD risk in a minority population. Similar to previous studies of PA interventions for migrant workers that employed enhanced socio-cognitive strategies such as motivation, feedback, role modeling, and social support to improve participants' exercise-related self-efficacy and foster health behavior changes [26, 27], the present findings support the effectiveness of socio-cognitive interventions that enhance self-efficacy, social support, and a sense of community for PA improvement and ultimately CVD risk reduction in KC migrant women.
Previous studies of PA interventions for middle-aged KC women mainly working as housekeepers, restaurant workers, and caregivers have primarily used pedometer-based walking programs [9, 25]. However, a limitation of these studies was that data on PA were collected by self-report methods, such as maintaining a walking diary. In this study, using a wearable device made it possible to improve the accuracy of the collected data and reduce participants' burden and bias related to self-reported data collection. The wearable device's close contact with the body made it possible to measure PA level accurately and obtain quantitative data continuously and in real-time . In particular, considering the occupational characteristics of KC middle-aged women who are unable to allot time for exercise after work, Fitbit has the advantage of being able to monitor PA level during daily life activities, occupational activities in the home, and community environments, and housework. Similar to other studies that reported positive health outcomes for Filipino-Americans  and African-American women  using a mobile app and Fitbit, this trial was meaningful as the mobile app and wearable device were suited to the participants in this study.
In this study, the intervention was divided into an adaptation period, during which the researchers guided participants to perform PA (weeks 1–12), and a maintenance period, during which participants were encouraged to engage in PA by themselves (weeks 13–24). As a result, improvements in health outcomes for the ET group were only significant at week 12 compared to the ST group, and no significant effects were observed at week 24 between both groups. Studies that employed the same design to examine PA effectiveness for a Latino ethnic group  and African-American women  showed similar results.
In a study that reported modest improvements in PA levels in African-American women in the maintenance period after an active intervention phase, strategies based on a strong behavioral theory that integrated various socio-cognitive factors including self-efficacy, decisional balance, perceived enjoyment of PA, social support from friends and family, and self-regulation were applied [3. Additionally, incentives were provided to those who completed the monthly surveys even during the six-month maintenance period. It must be noted that the present study did not collect data on participants' health outcome expectations or provide financial or motivational incentives during the 12-week adaptation period. Studies indicate that health outcome expectations are also related to an individual's self-efficacy for overcoming the barriers to health behavior from the perspective of social cognitive theory . Moreover, health outcome expectations motivate practicing healthy behaviors and an incentive for achieving positive health outcomes [35, 36]. In particular, when providing culturally tailored interventions for minority groups, health outcome expectations, as well as health beliefs and values, should be considered . These factors may influence the interaction between the researcher providing the intervention, the participants receiving it, and the associated health outcomes . Thus, when conducting long-term walking intervention studies on migrants, challenges related to adherence to health behaviors can be expected; however, during the early intervention period, people are more likely to continue to participate in the program, especially if health outcome expectations and financial or motivational incentives are provided [39, 40].
This study has several limitations. For the convenience of recruiting migrant women, which is a hard-to-reach group in the community, KC migrant women who verbally expressed their intention to participate at the recruitment site were selected as participants and randomly assigned. After providing verbal informed consent at the baseline assessment, the women participated in the intervention. However, subsequently, a number of women refused to participate for various reasons in initial phase of the study. The researcher's physical presence in a face-to-face setting may also be more likely to consent to research participation as a perceived social pressure to conform . Therefore, it is important to form suitable conditions such as a comfortable place when recruiting participants and to provide ample time so that they can consider whether they can afford to participate in the research. A literature review of strategies for sampling, recruitment, and participation in health research on socially vulnerable groups recommends a sufficient period of time for recruiting planned targets, building partnerships with community institutions, strengthening networks, and using tailored individualized approaches for follow-up . Future health intervention research for socially inaccessible groups such as migrants warrants more sufficient recruitment periods and having a community leader in building networks.
On the contrary, although the systematic and meta-analysis shows that intervention strategies based on multiple socio-cognitive factors have a positive influence on PA and health outcomes [43–45], these findings are limited by the fact that differences in the effectiveness of PA for health outcomes according to the level of each socio-cognitive factor has not been confirmed. Therefore, there is a limit to generalizing the results of this study, and based on the results of this study, further studies are needed to confirm the direct and indirect effects of social cognitive theory-based strategies on PA and health outcomes.