Methods: This will be a cross-sectional retrospective/prospective study population. The retrospective study will include data analysis of patients that preformed CPET as part of their clinical evaluation. In the prospective study, patients that are scheduled to perform CPET as part of their clinical evaluation will sign (or legal guardian) informed consent prior to participation. Patients will be recruited from the exercise clinic at the Pediatric Pulmonary Institute at the Rappaport Children's Hospital. Inclusion criteria: 1. Children and adults (age >7 years, height >125cm), with CF and non CF bronchiectasis. 2. Completed a maximal CPET test according to accepted criteria; (maximal VO2 > 80% predicted, maximal heart rate > 80% predicted, acceptable RER (RER > 1.0 in children (under 18 years), RER > 1.05 for adults) or reaching a VO2 plateau..3. Evidence of bronchiectasis in computed tomography (CT).