The ACP will use the application as developed for patients with COPD and tested to be effective in this population (Demeyer et al., 2017). The program includes 1) one-to-one semi-structured interview (V1) with the coach discussing the importance of physical activity, motivation, self-efficacy, barriers, favorite activities and (coping) strategies to become more active resulting in an individual action plan; 2) step counter (Fitbit; wrist or waist worn) providing direct feedback which automatically sends data to the smartphone via blue-tooth. Patients will be asked to wear this step counter every day during the intervention; 3) smartphone coaching application, installed on a smartphone and linked to the step counter, will provide automated coaching by displaying an individual activity goal (expressed as daily step count) and daily and weekly feedback on the performance (steps) of the patient. 4) phone calls by the coaches initiated in pre-defined situations.

The MCP includes 1) one-to-one semi-structured interview (V1) with the coach discussing the importance of physical activity, motivation, self-efficacy, barriers, favorite activities and (coping) strategies to become more active resulting in an individual action plan; 2) step counter (Fitbit, wrist or waist worn), that will be linked with a smartphone using the Fitbit application providing direct feedback. Patients can access the Fitbit application if they want to, but they will not receive personal feedback; 3) weekly phone calls by the coaches, interviewing patients on their progress, performance (steps) and feedback. The first goal is based on the physical activity level at the beginning of the coaching intervention (median of 4 days). The individual activity goal (expressed as daily step count) will be revised based on the patient's willingness to increase.

A semiautomated tele coaching program (application installed on a smartphone device with real time feedback and motivational messages) and a step counter (Fitbit Charge 4) providing direct feedback on total daily number of steps, walking time, time in at least moderate PA and movement intensity during walking.

(i.e. to what extent patients receiving the intervention consider it as appropriate) Acceptability will be assessed through quantitative data (a project-tailored questionnaire) and qualitative data collection (patient interview with open questions).

Patients will be asked to fill in a self-administered, project-tailored, multiple choice questionnaire on their experiences with the intervention.

Patient interviews with open questions will be conducted by the local PA coach in each center.

(i.e. the degree to which patients use the components of the intervention as it was designed) Actual usage of the custom application by patients will be assessed objectively through the smartphone app log (for participants in the ACP group). This will include information about completion of the app tasks and step counter data on a day-by-day basis and will be automatically collected in the back-end of the application.

Actual usage of the step counter (for participants in both intervention groups) will be defined based on the presence of step count data (ie, ≥70 steps for that day). The frequency at which patients looked at their step counter will be assessed subjectively in the project-tailored questionnaire.

(i.e. the extent to which the treatment can be successfully used within a given setting). Feasibility will be assessed through quantitative data (a project-tailored questionnaire) and qualitative data collection (patient interview with open questions).

Patients will be asked to report the smartphone intervention and use of the step counter and indicate if it was not too much of a burden to work with when they are asked how they have experienced the technical aspects of the intervention. Coaches will collect contact time with patients and preparation time in a logbook in an Excel file. Also, how many times patients are contacted and the number of technical problems will be collected.

PA will be objectively measured using the Dynaport Movemonitor (DAM, McRoberts, The Hague, The Netherlands), a small (106.6 x 58 x 11.5mm), light-weight CE marked tri-axial accelerometer with a sampling frequency of 100Hz. The Dynaport Movemonitor analyzes and expresses digital data not only in terms of locomotion and movement parameters, but also in terms of body posture. Data will be processed with commercially available software (MoveMonitor; McRoberts B.V., The Hague, The Netherlands). The monitor will be worn at the waist level using a comfortable elastic strap.

Patients will wear the monitor during 1 week before and after the intervention. They will be asked to wear the device continuously, except during bathing/showering and sleeping. Days with less than 8 hours of wearing time will be excluded from the analysis. Patients will not be included in the analysis if they did not have at least 4 valid weekdays of measurement.