Experimental Overview: Participants with CF will report to the laboratory on four separate visits. Visit 1 and 2 will occur before the participants go on drug (Orkambi) and will be separated by a minimum of 2 days between visits. Visit 3 and 4 will occur at 1 month and 3 months after initiating full dose of drug, respectively. On visit 1, participants will complete medical history screening, anthropometric measurements, pulmonary function assessment, and a symptom limited incremental cycle exercise test to determine peak incremental work rate. On visit 2, participants will complete chronic activity-related dyspnea, quality of life, and physical activity questionnaires, perform pulmonary function testing followed by a constant-load cycle exercise test at 80% of peak incremental work rate. Visits 3 and 4 will include chronic activity-related dyspnea, quality of life, and physical activity questionnaires, pulmonary function testing, and a constant-load cycle exercise test at 80% of peak incremental work rate. Detailed physiological and sensory measurements will be obtained during the exercise test sessions. Data from the constant-load cycle exercise tests performed on visits 2, 3, and 4 will address our hypothesis.