The level of physical activity (PA) has been shown to be an important predictor for morbidity and mortality in patients with chronic respiratory diseases such as COPD and more recently Idiopathic Pulmonary Fibrosis. Physical inactivity is a common feature of patients with chronic respiratory diseases. Whereas pulmonary rehabilitation is known to result in benefits in exercise capacity, symptoms and quality of life, these gains will not automatically translate into increases in physical activity. Therefore, the present study aims to investigate the effect of a physical activity coaching program on the physical activity level of patients with interstitial lung disease.

The present study aims to

1) primary objective: To explore the magnitude of the effect of a semi-automated tele coaching intervention to enhance physical activity in patients with interstitial lung disease, as measured at 12 weeks, expressed as mean daily step count.

2) Secondary objectives:

1. To test the magnitude of the effect of a 12 weeks coaching intervention on mean time in at least moderate intense activity, walking time, movement intensity, activity bout duration, exercise capacity, quadriceps force and health status.
2. To investigate the patient's experience with this intervention
3. To test the effect of a 12 weeks coaching intervention on the physical activity from a patient experience.
4. To explore the relation between physical activity and vitamin D

Therefore, the study will include stable patients with interstitial lung disease who will be randomized into an intervention (semi-automated coaching intervention) and control (usual care) group. The study consists of a total of 3 visits.

• visit 1: Screening visit
• visit 2: Randomization visits, scheduled 1-2 weeks after visit 1
• visit 3: Follow-up visit, schedules 12 weeks after visit 2

Patients will be randomized into the intervention and control group. In both groups patients will receive information about the importance of being physically active and the physical activity recommendations provided by the world health organization. This information will be provided in a leaflet that will be discussed in an education session (one-to-one) of 10-15 minutes.

1. The control group will receive usual care together with the educational information.
2. Patients in the intervention group will receive a multicomponent tele coaching intervention that consists of 1) education about the importance of physical activity and a one-to-one interview with the coach discussing motivation and barriers to be active, 2) a step counter providing direct feedback, 3) application installed on a smartphone providing an adaptive goal and daily and weekly feedback and 4) contact with the coach if the patient is not compliant with the intervention or not increasing physical activity. The patient is asked to have a daily interaction with the smartphone application.

Inclusion Criteria:

1. Stable patients, older than 18 year, with a diagnosis of interstitial lung disease
2. Understand and able to work with a smartphone application, as judged by the investigator
3. On stable pharmacotherapy
4. DLCO ≥30%predicted

Exclusion Criteria:

1. On the waiting list for a lung transplantation
2. Life expectancy below 3 months
3. Respiratory tract infection or an exacerbation or change in maintenance medication within 4 weeks before study enrolment
4. Extra pulmonary impairments, unrelated to the underlying lung disease, interfering with physical activity