RExA-CF is investing if results from exercise tests (the Chester Step Test and the One-Minute Sit-to-Stand test) completed face to face are comparable to results of the same tests completed via a virtual teleconferencing platform. The study involves two exercise testing sessions (one face-to-face and one via a video link), with participants being randomised to complete the two exercise tests (the 1-minute sit-to-stand test and the Chester Step test). The two testing sessions will be completed within three weeks of each other, the order of which will be randomly allocated. One session will be completed face-to-face during a pre-arranged visit to the hospital, the other test session will be completed through a video call at a time convenient to the participants. After the second testing session participants will be asked some questions about the face-to-face and video tests to get their views about the two formats.

Inclusion Criteria:

• Diagnosis of cystic fibrosis (as confirmed by standard criteria)
• Sixteen years of age or over
• Home internet access
• Stable CF disease as judged by the medical team
• Registered with the Royal Brompton Hospital adult CF team

Exclusion Criteria:

• Inability to give consent for treatment or measurement
• Current participation in another interventional study
• Current moderate haemoptysis (greater than streaking in the sputum)
• Pregnancy
• Forced expiratory volume in 1 second (FEV1) below 30% predicted
• Dependency upon oxygen therapy (with home oxygen concentrators or portable oxygen cylinders) or non-invasive ventilation (NIV)
• Current neurological or musculoskeletal injury which would prevent completion of exercise tests
• Inability to complete the second set of exercise tests within three weeks