Objectives: 1.- To compare the level of oxygenation achieved during muscular training with conventional oxygen systems (nasal cannulas) versus nasal High-flow oxygen therapy. 2.-To compare benefits achieved with both systems, in terms of: level of exercise during training; effort tolerance in the 6 minutes walking test (6MWT); improvement of dyspnoea and Health-related quality of life (HRQoL). And analyse the effects of nasal High-flow oxygen therapy on the acute exercise in a subgroup of patients.

Method: Multicentric randomized clinical trial. Patients with ILD in fibrotic phase who present oxygen desaturation during 6MWT (SpO2 mean ≤ 85%) will be included consecutively. Will be randomized in two groups: ILD patients with conventional oxygen (EPIDOC) and ILD patients with nasal High-Flow oxygen therapy (EPIDOAF). Both groups will perform a Pulmonary Rehabilitation Program. Oxygen will be titrated respectively to flow and FiO2 needed to maintain SpO2 ≥ 90% during training with both systems. Evaluation measures: SpO2 during training in both groups; dyspnoea (mMRC scale and CRQ dyspnoea); exercise capacity (6MWT) and HRQoL (self- administered KBILD questionnaire and SF36). In a subgroup of patients will be compared time of endurance exercise to evaluate the effects of nasal high-flow oxygen therapy in the acute exercise.

Inclusion Criteria:

• Age > 30 years old
• Diagnostic of ILD according to the national and international guidelines 23
• Being clinically stable the previous 4 weeks
• Acceptance to participate in the trial

Exclusion Criteria:

• Have been enrolled in a PR program in the last previous 6 months
• Respiratory Diseases other than ILD or severe comorbidities
• Osteoarticular diseases which don't allow training
• End-stage ILD, treatment with opiates or survival < 6 months
• Cognitive alterations that preclude colaboration