The fourth intervention group (n= 30 professional drivers) will receive app-supported exercise therapy. The intervention will be based on principles of high-intensity training exercises that focus on the improvement of cardiorespiratory exercise capacity, as well as on the reduction of stress levels during work. Participants will receive instructions via the app to do some short, vigorous exercises adapted to their work environment at regular intervals, e.g., bending-and-stretching exercises with a weight in their hands, walking up and down the stairs of their vehicle for a few minutes, etc.

The active control group (n= 20 professional drivers) will get a conventional intervention to reduce stress, e.g., mindfulness.

The passive control group (n= 20 professional drivers) will get no intervention and will continue as normal without receiving any feedback.

The second intervention group (n= 30 professional drivers) will receive personalized tailored feedback to reduce chronic stress and sleepiness/fatigue. The advice involves personalized (semi-)automatic feedback to drivers about a reduced stress level via the mobile app with automatic reports, as well as post-intervention during the next work break or at the end of the workday, based on the preferences of the driver. The (semi-)automatic feedback is based on the theory of Stages of Change, by which a driver will only receive relevant feedback based on their attitude and willingness during daily life.

The third intervention group (n= 30 professional drivers) will receive both real-time feedback related to acute stress and sleepiness/fatigue, as well as personalized tailored feedback related to chronic stress and sleepiness/fatigue, similar as in the first and second intervention groups.

The fourth intervention group (n= 30 professional drivers) will receive app-supported exercise therapy. The intervention will be based on principles of high-intensity training exercises that focus on the improvement of cardiorespiratory exercise capacity, as well as on the reduction of stress levels during work. Participants will receive instructions via the app to do some short, vigorous exercises adapted to their work environment at regular intervals, e.g., bending-and-stretching exercises with a weight in their hands, walking up and down the stairs of their vehicle for a few minutes, etc.

The active control group (n= 20 professional drivers) will get a conventional intervention to reduce stress, e.g., mindfulness.

Measuring health-related quality of life, consisting of both a physical and mental component. The SF-36 consists of eight scaled scores, which are the weighted sums of the questions in their section. Each scale is directly transformed into a 0-100 scale. The higher the score the less disability i.e., a score of zero is equivalent to maximum disability and a score of 100 is equivalent to no disability.

Measuring perceived stress. The questions ask about feelings and thoughts during the last month. In each case, respondents are asked how often they felt a certain way on a five-point scale from 'never' to 'very often'. Answers are then scored as follow: Never = 0; Almost never = 1; Sometimes = 2; Fairly often = 3; Very often = 4. To calculate a total PSS score, responses to the four positively stated items (items 4, 5, 7 and 8) first need to be reversed (i.e. 0 => 4; 1 => 3; 2 => 2; 3 => 1; 4 => 0). The PSS score is then obtained by summing across all items. Higher scores indicate higher levels of perceived stress.

A 16-item instrument extracted from the Driver Behaviour Inventory that measures general driver stress. The DBI-Gen consists of 16 items that tap a general disposition, or "trait" susceptibility, to driver stress. Responses are made on a Likert scale ranging from 0 to 100, indicating the level of agreement with each statement. Scoring consisted of the mean response to the 16 tems, with higher scores indicating greater trait driver stress susceptibility.

Measuring a broad and stable sense of personal competence to deal effectively with a variety of stressful situations. The total score is calculated by finding the sum of all 10 items. For the GSE, the total score ranges between 10 and 40, with a higher score indicating more self-efficacy.

A 42-item self-report instrument designed to measure the related negative emotional states of depression, anxiety, tension/stress.The DASS assesses negative emotional symptoms by using a 4-point Likert scale, ranging from 0 to 3. It has 3 subscales (depression, anxiety, and stress) with 14 items in each subscale for the DASS 42. These subscales are scored by the addition of the total item scores, which can range from 0 to 42. Maximum score: 126 for the 42-item DASS. A higher score on the DASS indicates greater severity or frequency of these negative emotional symptoms.

A short, valid, reliable and easy to administer unidimensional fatigue questionnaire. The FAS is a 10-item general fatigue questionnaire to assess fatigue. Five questions reflect physical fatigue and 5 questions (questions 3 and 6-9) mental fatigue. An answer to every question has to be given, even if the person does not have any complaints at the moment. Scores on question 4 and 10 should be recoded (1=5, 2=4, 3=3, 4=2, 5=1). Subsequently, the total FAS score can be calculated by summing the scores on all questions (recoded scores for questions 4 and 10). The total score ranges from 10 to 50. A total FAS score < 22 indicates no fatigue, a score ≥ 22 indicates fatigue.

To measure daytime sleepiness, asking the subject how likely he/she is to doze off or fall asleep in different situations of everyday life. The test is a list of eight situations in which the respondents rates his/her tendency to become sleepy on a scale of 0, no chance of dozing, to 3, high chance of dozing. All answers to the questions need to be added.The total score is based on a scale of 0 to 24, with a higher score means a higher respondent's sleepiness.