Self-efficacy
We will use two indicators to measure self-efficacy. First, g
eneral self-efficacy will be assessed using a Dutch translation of the 12-item General Self-Efficacy Scale [
63]. An example item is: “If I made a decision to do something, I will do it” (1 =
strongly disagree, 5 =
strongly agree). Psychometric properties of this scale are good [
62]. Secondly, w
ork-related self-efficacy will be measured by means of the subscale ‘Competence’ of the Utrecht Burnout Scale [
59]. An example item is: “If I make plans, I am convinced I will succeed in executing them” (0 =
never, 6 =
every day). Validity and reliability of the scale are good [
60].
Sleep
To measure employees’
sleep quality, the 6-item sleep quality scale of the Dutch Questionnaire on the Experience and Evaluation of work will be used [
64]. The scale measures the three main components of insomnia (i.e. difficulties in: initiating sleep, maintaining sleep, and restorative sleep) and overall sleep. An example item is: ‘I often wake up several times during the night’ (0 =
no, 1 =
yes). Furthermore, participants report their average sleep duration (hours, minutes) as an indicator of
sleep quantity. Reliability and validity of the scale are found to be good [
60].
Work ability will be measured by means of a single item [
65], namely “Can you indicate how you rate your current work ability when you compare it with your life-time best?” (0 =
completely unable to work, 10 =
work ability at its best). This item has been shown to be a good alternative to more comprehensive measures of work ability [
65].
Cognitive functioning
Employees’ cognitive functioning will be measured by means of four indicators: one self-report measure and three cognitive performance tests.
Self-reported cognitive problems will be measured with a Dutch translation of the Cognitive Failure Questionnaire (CFQ [
66]). This questionnaire measures the frequency of every day cognitive failures and consists of 25 items. An example question is: “Do you read something and find you have not been thinking about it and must read it again?” (1 =
never, 5 =
very often). Previous research shows that the CFQ has excellent psychometric properties [
67].
Three types of executive functions (i.e. ‘updating’, ‘switching’, and ‘inhibition’), which are considered as basic executive functions and can be clearly and precisely described [
68], will be measured with three validated tests. These tests will only be conducted pre (T0) and post (T6) intervention and not at follow up, because of possible learning effects. The tests will be provided in a counterbalanced order to the participants. However, for each participant the order of tests is similar pre and post intervention. Individual appointments in the lab of the university will be planned. Completion of the three cognitive tests, including filling out the subjective costs, takes about 30 min.
Updating will be measured with the 2-Back Task [
69]
. Updating refers to the capability of actively manipulating relevant information in working memory [
68]. During the task, 284 stimuli (the letters: b, d, g, p, t, and v) are displayed one by one in the centre of the screen. Each letter will be displayed for 450 ms, and the time between the letters will be 750 ms. The letters are presented in a quasi-randomly order in both capital and small letters. When the displayed letter is similar to the letter that is shown two screens before, participants have to push a button on a button-box (target rate: 32.5 %). For a correct response, no distinction is made between capital and small letters. The number of correct responses will be taken as an indicator of updating.
Switching refers to the ability to shift between tasks [
68], and will be assessed by the Matching Task [
70,
71]. In this task, four different geometric figures (a circle, a hexagon, a square, and a triangle), presented in the colors blue, green, red, or yellow are used as stimuli. The task consists of 31 task runs, each consisting of on average six trials (range: 4–8 trials). During a trial, a colored reference figure is displayed in the upper half of the screen, and four colored match figures are shown in the lower half of the screen. Participants will be instructed to match the reference figure to one of the match figures according to shape or color. Whether participants have to match according to shape or color, will be randomly chosen and indicated by a cue that is displayed for 1000 ms. Participants can push one of four buttons on the keyboard which corresponds to one of the four match figures in the lower half of the screen. During one single task run, participants have to match either according to color or shape. The color-shape combinations are shown in a way that there is one ‘right’ option. Half of all task runs consisted of ‘switch’ runs, in which the type of cue differs from the previous run. The other half consists of ‘repetition’ runs, in which the type of cue is identical to the previous run. The duration of the test is approximately six minutes. Both the mean reaction time for switch runs and repetition runs will be used as an outcome measure for switching (for more detailed information about this task, see [
70]).
Inhibition addresses one’s capability to deliberately inhibit dominant and automatic responses to certain stressors [
68]. Inhibition will be measured with the Sustained-Attention-to-Response Test (SART [
72]). During this test, digits (ranging from 1–9) are displayed one-by-one in the centre of the screen. Participants are instructed to push a button on a button-box when a digit appears on the screen, except when the digit is a ‘3’, which occurs in 11.1 % of the cases. A total of 450 digits will be presented, each with a duration of 250 ms. The interval between digits is 850 ms. The number of inhibition errors (thus, when a participant presses the button when a ‘3’ appears on the screen), will be taken as a measure for inhibition.
To obtain more insight into cognitive functioning, we will additionally evaluate the
subjective costs (fatigue, motivation, demands, and effort) associated with doing these tests [
73,
74]. These
subjective costs will be measured using single item measures, answered on a scale from 1 (
not at all) to 10 (
very much). Before doing the cognitive tests, participants will rate how motivated they are to do the tests. Fatigue will be measured prior to and after the tests. In addition, after each cognitive test, participants will be asked to score how demanding the test had been. After completing all the tests, participants indicate how much effort they spent when doing the tests.
Aerobic fitness
We will measure aerobic fitness using the estimated maximal oxygen uptake (VO
2max), obtained from the UKK walk test [
75]. This test has found to be valid and feasible for a healthy adult population [
75]. During this test, participants have to walk 2 km as fast as possible. The test will take place on a 400 m outdoor track in groups of (maximum) ten participants. Participants start individually every 30s. The instruction is as follows: “Walk the distance as fast as you can, but do not risk your health”. Immediately after the walk, the heart rate and walking time will be measured. The variables used to calculate VO
2max are walking time, heart rate, body weight, height, and gender (see [
75] for exact equations).
We will also measure participants’ subjective costs of doing the UKK walk test. The questions used for this purpose are similar to those asked before and after the cognitive tasks, except that we add another question about how ‘short of breath’ participants are immediately after the test. Completion of the test, including filling out the items about subjective costs, takes about 25 min.