NCT03109912.

Methods	Design: parallel RCT ("Do More, B'More, Live Fit"), duration 6 months; single‐centre study at Johns Hopkins University, Baltimore, US.
Participants	Enrollment goal: 60 participants with CF. Inclusion criteria: males and females aged 12 ‐ 21 years old with CF and cared for at Johns Hopkins; participants must have a smartphone and/or computer with universal serial bus (USB) to set‐up FitBit Flex. Exclusion criteria: FEV1 < 40% predicted; individuals already participating in vigorous physical activity (as assessed by the study team) in year‐round organised sports and/or aerobic exercise for longer than 30 minutes more than 5x per weeks may or may not be included in this study at the discretion of the principal investigator and study team.
Interventions	Intervention group: at baseline assessment participants given individualised exercise prescriptions with the aim of achieving 30‐minutes of an endurance‐style exercise (team sports, walking, jump roping, stair climbing or more complex Tabata‐style workouts) 5 times/week for 6 months. At 4‐6 weeks and 8‐10 weeks post‐enrolment, participants attend a follow‐up 30‐minute session which will vary based on initial assessment and previous exercise prescription success, but will include strength training for major muscles groups and/or flexibility exercises with yoga as well as reinforcement of previously learned techniques with additional individualised recommendations. Participants will also receive motivational messages starting 14 days after enrolment via preferred contact method (SMS, telephone call and/or email) every 3‐4 days over the 6‐month study period. Participants also given access to "Do More, B'More, Live Fit" web page which includes spotlighted exercises, instructional exercise photos and videos; also invited to join the "Do More, B'More, Live Fit" Activity Group via the FitBit Dashboard and to friend the study team members and other exercise‐intervention participants in order to take part in FitBit step‐goal challenges. Control group: at baseline assessment, the FitBit daily step goal is set at the manufacturer standard 10,000 steps. At routine clinic visits, baseline and follow‐up assessments (3 and 6 month clinic visits) participants given generic, non‐personalised encouragement and recommendations (if requested by the participant) for physical activity. At the 3‐ and 6‐month visits, exercise is reinforced with generic encouragement, export FitBit data and review any missing data concerning for equipment failure or user error.
Outcomes	Included in this study were: Primary outcomes: LCI (LCI 2.5 and LCI 5.0); daily activity via FitBit step count and daily step count (mean, median and highest daily) recorded through participant FitBit flex. Secondary outcomes: FEV1 % predicted; self‐reported physical activity (Habitual Activity estimation Scale); HRQoL (CFQ‐R); exercise capacity (modified shuttle walk test); acceptability and feasibility of the programme using semi‐structured interviews.
Notes	This study evaluates the "Do More, B'More, Live Fit", a 6‐month fitness programme designed to optimise exercise habits of participants with CF through structured exercises with personalised coaching, exercise equipment including the FitBit Flex, online support and motivational messages delivered electronically. The intervention incorporates fitness preferences and encompasses endurance, strength and flexibility exercises while adjusting to physical fitness needs. The hypothesis is that intervention participants will have increased and sustained engagement and better health outcomes compared to control group participants.