High-Intensity Interval Training Is Effective at Increasing Exercise Endurance Capacity and Is Well Tolerated by Adults with Cystic Fibrosis

Background: To optimize outcomes in people with cystic fibrosis (CF), guidelines recommend 30 to 60 min of moderate-intensity aerobic exercise on most days. Accumulating this volume of exercise contributes importantly to the substantial treatment burden associated with CF. Therefore, the main aim of this study was to investigate the effects of low-volume high-intensity interval training (HIIT) on exercise capacity in people with CF. Methods: This randomized controlled trial included people with CF aged ≥15 years, who were allocated to either eight weeks of thrice-weekly 10-min sessions of HIIT (experimental group) or eight weeks of weekly contact (control group). Before and after the intervention period, participants completed measurements of time to symptom limitation (Tlim) during a constant work rate cycle ergometry test (primary outcome), and maximal work rate (Wmax) during a ramp-based cycle ergometry test and health-related quality of life (HRQoL). Results: Fourteen participants (median (IQR) age 31 (28, 35) years, forced expiratory volume in 1 second (FEV1) 61 (45, 80) % predicted) were included (seven in each group). Compared to the control group, participants in the experimental group demonstrated a greater magnitude of change in Tlim, Wmax (p = 0.017 for both) and in the physical function domain of HRQoL (p = 0.03). No other between-group differences were demonstrated. Mild post-exercise muscle soreness was reported on a single occasion by four participants. Overall, participants attended 93% of all HIIT sessions. Discussion: Eight weeks of low-volume (i.e., 30-min/week) HIIT produced gains in exercise capacity and self-reported physical function and was well tolerated by people with CF.

. Behavior change techniques within high intensity interval training intervention.

Description of intervention component Behavior change techniques identified Confidence
When in attendance at the HIIT sessions, participants were asked to increase the intensity of exercise each week depending on what they were able to tolerate (based on their perceived level of leg muscle fatigue and breathlessness, as a proxy measure of increasing exercise capacity). Sessions commenced at 60% of the Wmax in week 1, with the aim of achieving 80% of the Wmax by the end of week 2 (lead-in phase), and as symptoms permit from week 3 to week 8 of the program.
Goal setting (behavior) Graded tasks 2 2 Participants were provided with detailed instructions to attend the physiotherapy department (at their preferred hospital location) two, and then three, times per week for 8 weeks to undertake each HIIT session. Information was also provided on parking options at the hospital location via a map (as required). The same physiotherapist was present for all HIIT sessions throughout the program. The participants were able to contact the physiotherapist by phone or email to discuss booking sessions, various aspects of the program and any issues encountered.

Action planning
Instruction on how to perform the behavior Social support (unspecified) 2 2 2 Participants were provided with verbal and written (an information sheet) instructions on post-exercise muscle soreness and how to manage potential symptoms prior to undertaking their first HIIT session. The verbal instructions were reiterated weekly and participants were advised to inform the physiotherapist of any delayed symptoms related to the HIIT.
Information about health consequences 2 Discussion occurred with participants prior to commencing each HIIT session regarding the previous intensity achieved (based on work rate, symptoms and heart rate) as well as the goal for this session. At the completion of each session, further discussion of the markers occurred in order to reflect on the intensity achieved during the session.

Review behavior goal(s)
Feedback on outcome(s) of behavior 2 2 The intensity of exercise (in Watts, as a percentage of the participant's baseline level of fitness), and achievements of other participants (who had already completed the intervention period) were discussed with current participants to reflect on the progress they had made, in comparison to the progress of others that had been made at similar time points.

Social comparison 1
Participants were provided with verbal (by the physiotherapist) and visual (Watt display on the computer on the cycle ergometer) cues regarding how far they were through each interval, the intensity achieved during the interval and the time left for HIIT session. Observations (HR, SpO2 and Borg scores, and Watts on the cycle ergometer) were monitored by the physiotherapist throughout each HIIT session and verbal feedback was provided by the physiotherapist to reassure the participant at regular time intervals on how they were responding to the session.

Biofeedback
Feedback on behavior 2 2 In order to convey the physiotherapist's confidence in the participant being able to achieve a specific intensity of exercise, participants were reminded about the intensity they were able to achieve in previous HIIT sessions, despite uncomfortable symptoms that may have been associated with the exercise. In addition, the physiotherapist provided positive reinforcement and encouragement when a particular intensity was achieved (i.e. based on Watts) despite the difficulty in achieving the behavior (i.e., onset of leg muscle fatigue and breathlessness).

Social reward
Verbal persuasion about capability Focus on past success 2 1 2 The participants were advised that to have 'completed' the intervention, they were required to attend at least 70% of sessions. The session count was discussed with the participant weekly in order to plan for the remaining sessions/weeks and set goals for the exercise intensity to aim for in the remaining weeks.

Review behavior goal(s)
Feedback on behavior 2 2 2 If a participant missed a session(s), they were permitted to extend the program by a maximum of 2 weeks. This was outlined to the participant at the start of the program, and if they had to cancel a session for any reason (life commitments, being medically unwell etc.) Restructuring the physical environment 1 Abbreviations: HR: heart rate, SpO2: oxygen saturation, Wmax: maximal work rate. A '2' in the confidence column of the table indicates that the authors confident 'beyond reasonable doubt' that the technique was present. A '1' in the confidence column indicates that the technique was present 'in all probability'.