Table 1.

Overview of the protocol that was used in the study with durations of the activity and rest immediately after the activity indicated in square brackets

Heart rate at rest [5]
Indoor activities
1. Stacking groceries [3, 1]
2. Desk work [2, 1]
3. Vacuuming [3, 2]
4. Sitting resting [3, 1]
5. aCycling fitness test (60 W) [6, 5]
6. aWalking treadmill - 3 km/h – 0% incline [3, 2]
7. Standing resting [1, 1]
8. aWalking treadmill - 5 km/h - 0% incline [3, 2]
9. Folding towels [3, 1]
10.aWalking treadmill - 5 km/h - 0% incline - carrying 4 kg [3, 3]
11. Cooking or Washing dishes [3, 1]
12. aWalking treadmill - 3 km/h - 5% [3, 3]
13. Cleaning table [3, 1]
14. aCross trainer - 60 W [3, 5]
15. Yoga [3, 1]
Switch to self-paced/outdoor activities
16. Walking upstairs (indoors) [1, 2]
17. Walking downstairs (indoors) [1, 2]
18. Walking, hands free [2, 1]
19. Walking, hands in pockets [2, 1]
20. Walking, carrying a bag [2, 1]
21. Cycling [3, 2]

After step 15, a pause of 5–10 min was required to replace the battery of the K4b² and to prepare participants for doing the self-paced activities that were executed indoors and outdoors. Before the activities, all participants started with a 5-min measurement of heart rate at rest so all participants started at a similar steady state in rest. Note that, due to weather conditions, for some participants, the self-paced activities were performed indoors. Also note that cooking and dishwashing (11) were “role-playing” activities mimicking the actual activities. Activities marked with an 'a'  were fixed paced activities enforced by either setting a specific speed of the respective exercise machine or by monitoring by the study assistant