Bus drivers are predisposed to work-related musculoskeletal disorders as they have to maintain the same driving posture continuously and sit for a long time at work during workdays [1]. Moreover, they are at high risk group for cardiovascular disease (CVD) due to long work hours of 52 or more hours per week and irregular shifts [2]. In particular, bus drivers are exposed to poor working environments, including insufficient breaks due to short bus dispatch intervals, irregular mealtimes, and exposure to noise and whole-body vibration while driving [1, 2, 3]. Work schedules of Korean bus drivers is 12-hour shifts or 8-hour shifts, and their dispatch times and break times vary from workplace [4]. A systematic review of health and wellness among long-haul truck and bus drivers in the US and Canada revealed vulnerability to risk factors, such as lack of physical activity, which may cause CVD and diabetes [5].

Because lack of physical activity is a significant factor in increasing health risks, such as coronary artery disease and CVD [6], it is essential to increase physical activity to prevent chronic diseases and promote wellness. According to the Korea National Health and Nutrition Examination Survey (KNAHES), the proportion of adults aged 19~64 who walked for at least 150 minutes over the previous week showed a decreasing trend from 58.3% in 2014 to 47.8% in 2019 [7]. Among men, in particular, the proportion decreased with age, with 68.4% of men between 19 and 29 indicating walking compared to 40.9% among men between 50 and 59, and the downward trend was clearer in men than in women of the same age ranges [7]. As a large number of bus drivers are middle-aged or older men who sit on the job for prolonged periods of driving and non-driving time [2], a program for bus drivers to increase physical activities should be developed.

As wearable tracking devices have been developed, which can influence health behaviors such as increasing physical activity with rapid advancements in information communication technology, research on mobile Health (mHealth) to promote physical activity is actively conducted [8]. Wearable tracking devices have been demonstrated to help study participants change health behaviors by providing daily steps and pulse rate data, thereby allowing people to self-monitor their health behavior [9]. However, a systematic review on the effectiveness of mHealth reported that positive effects of mHealth were not consistently observed, as it would be difficult to continue improving physical activity by using a wearable tracking device alone due to limitations of self-motivation [10]. Therefore, the mHealth program to improve physical activity for bus drivers should be considered by incorporating effective motivational strategies, such as text messages, photo messages, apps, and personal coaching [10, 11, 12]. Text messaging on phones is currently under investigation as a form of mHealth service owing to its ability to continuously motivate users by sending motivational messages in real-time without temporal or spatial restrictions [11]. Moreover, the effectiveness can be maximized by reinforcing individualized goal-setting and customized health coaching to promote physical activity custom fit each user's characteristics [12].

Specifically, bus drivers are considered a vulnerable population for participating in health promotion or wellness programs by institutions and public health centers due to unfavorable working environments with irregular shifts and long working hours [13]. Given that this population is more likely to develop various chronic diseases, customized interventions are required to promote physical activity provided at their workplaces or everyday lives. The mHealth program using mobile health technology might effectively engage the bus drivers in wellness programs [14]. To date, however, studies on mHealth programs for promoting physical activity among bus drivers are lacking, even though a large number of studies have examined the effectiveness of mHealth programs targeting adult men and women of various ages. Therefore, this study aimed to develop a mHealth program to promote physical activity using a wearable devices (Fitbit Charge HR, FB405, San Francisco, US) and health coaching, and then examine the effectiveness of the program on daily steps, exercise self-efficacy, autonomous motivation to exercise, and physiological indices, such as blood pressure and blood glucose level.

The mean age of the participants was 53.8, which aged drivers are required to accurately recognize their health status and establish health promoting behavior for the rest of their healthier working life [20]. Literature reviews on workers in transportation companies have demonstrated that drivers are a highly vulnerable working population with limited opportunities to access resources to improve their health and wellness due to poor working conditions [5, 20, 21]. Therefore, as it is necessary to develop a wellness program for bus drivers, the mHealth program using Fitbit and health coaching for promoting physical activity is developed to improve drivers' wellness.

Our findings indicated that daily steps in the experimental group significantly increased by over 3,000 steps after participation in the mHealth program, whereas daily steps in the control group did not change, with a significant between-group difference. These results were in line with those of previous studies using a smartphone app-based walking program and an exercise program using a pedometer among taxi drivers, which found that the daily steps increased by 600~2,000 steps in the experimental group, with significant differences between experimental and control group [22]. The reason for a significant increase of daily steps of drivers in the experimental group is due to the continuous motivation provided by the weekly face-to-face health coaching to monitor the seven-day physical activity level and check achievement of long-term and short-term goals on a weekly basis. In addition, motivational text messages and customized photo messages visualizing daily steps over the last seven days would influence the participants in achieving their short-term goals on daily steps.

Exercise self-efficacy in the experimental group greatly improved after the mHealth program, while the control group showed little change, with a statistically significant difference between the two groups. This finding was consistent with previous studies, which reported significant increases in exercise self-efficacy after participation in interventions using Fitbit or smartphone apps [22, 23, 24]. Exercise self-efficacy refers to confidence regarding one's own ability to continue performing exercise under any circumstances and is an important factor in self-initiating and maintaining exercise [25]. Bandura [26] argued that self-efficacy stems from the experience of mastering health behavior, verbal persuasion, vicarious experience, and physiological feedback. Exercise self-efficacy in the present study probably increased, as the mHealth program helped the participants gain the experience of goal achievement through setting short-term and long-term goals for daily walking steps and supporting them during individual health coaching. Moreover, it is possible that exercise self-efficacy probably increased due to vicarious experience, as the researcher made weekly visits to the transportation company to meet bus drivers and provided opportunities to seeing other similar drivers performing an exercise successfully.

Systolic and diastolic blood pressure significantly decreased in the experimental and control groups; however, the between-group difference was not statistically significant. As blood pressure decreased even in the control group, which received only Fitbits, the significant decrease in systolic and diastolic blood pressure in the experimental group cannot be considered an effect of the mHealth program. According to the systematic review on the relationships between blood pressure and cardiovascular disease, the risk for major CVD significantly decreases by reducing systolic and diastolic blood pressure by 10 mmHg [27]. The participants in this study were men in their 50s, and decreased risk for major CVD due to a reduction of blood pressure by 5~8mmHg in the experimental and control groups is of significance from the perspective of health promotion and disease prevention among middle-aged men.

This study was the first to examine the effectiveness of the mHealth program for wellness that could be applied at the workplace in transportation service companies by using Fitbit and health coaching to promote physical activity among bus drivers. In addition, the bus drivers' physical activity was objectively assessed using Fitbit to count the number of steps. However, this study had some limitations. First, as participants were conveniently sampled from workers in city bus transportation companies in a single small-to-medium city, the results may not be generalizable. A follow-up study should be conducted with workers across several companies providing various transportation services, considering city size and company characteristics. Second, participants were not randomly assigned to either the experimental or control group based on the bus company they worked for; therefore, intervention outcomes may have been influenced by exogenous variables. In the future, the effects of the mHealth program should be tested in a randomized control group study. Third, it is necessary to conduct a follow-up study with a larger number of participants to increase the effect on the research findings since statistical analysis was performed with a smaller number of data. Finally, this program can be performed only for those who can use wearable devices and smartphone.

This study aimed to develop a mHealth program for bus drivers using Fitbit and health coaching to improve physical activity and examine the effectiveness of the mHealth program on the daily steps, exercise self-efficacy, autonomous motivation to exercise, and physiological indices including blood pressure and blood glucose level. The findings demonstrated that the mHealth program was effectively increased the number of steps and exercise self-efficacy, including among male workers in their 50s who were not physically active and were difficult to visit public health centers due to their shiftwork. The mHealth program is expected to create healthy and happy workplaces if established as a workplace wellness program in the transportation companies.

These results suggest several implications. First, while the mHealth program was effective in increasing the number of steps and exercise self-efficacy in bus drivers, autonomous exercise motivation did not significantly improve. Autonomous motivation to exercise refers to a psychological need to self-initiate and maintain exercise [19]. Individuals with stronger autonomous motivation actively perform exercises based on personal beliefs and value systems rather than external pressure; therefore, autonomous motivation is critical in performing exercise persistently [28]. The effect of the mHealth program on autonomous motivation to exercise should be re-evaluated after the program is modified by adding a suitable strategy to reinforce it. Second, the mHealth program to improve bus drivers' wellness did not include a nutrition component. The mHealth program consisting of physical activity and other components, such as nutrition and stress management, could be added. Recently, Korean public health centers have provided various mobile health programs including physical activities and good nutrition for community residents with health risk factors. Such mobile health program by public health centers should be targeted vulnerable populations including bus drivers, homeless, etc.