Figure 2.

The user journey of the app’s challenge function is depicted. Upon pressing the “start” button located at the lower part of the screen, the timer inside the green circle begins a countdown (initially set to 15 minutes). The numbers above the green circle indicate the remaining steps required to complete the challenge before the timer expires (initially set to 1500 steps). An example illustrating the progress of the challenge is presented in the middle of the figure (in this case, indicating the need to walk 1084 steps within 10 minutes and 22 seconds). Upon successful completion of the challenge, the app announces its accomplishment.