Shortness of breath (dyspnea) during exercise is a major source of distress and is a commonly reported symptom in patients with cystic fibrosis (CF). A recent treatment option known as Orkambi, which combines the drugs lumacaftor and ivacaftor, may be used in patients with CF to help improve lung health. However, the effects of this combination therapy on dyspnea and exercise performance, a known predictor of survival in CF, are not clear. The investigators aim to understand the effects of Orkambi on these symptoms and to gain new insight into the potential health improvements in CF from using this treatment option.