The InterWalk Application The IW App is a personal trainer as well as a monitor unit, which allows continuous and automatic transmission of physical activity data to a central data base in DD2. The IW app guides the user in IWT with repeated cycles of 3 minutes fast and slow walking. During IWT the app provides the patients with continuous feedback on the walking intensity (10). The feedback is personalized through a standardized eight-minute walking test, performed before engaging in IWT. The patients are able to track exercise history and receive historic feedback on the quality of the IWT sessions. The feedback system employs the on-board accelerometer and GPS system to assess intensity and geographical location.