Secondary outcome measures

The secondary outcome measures were those that had the potential to be primary or secondary outcomes in a definitive clinical trial. These were: exercise capacity (6 min walk test),¹⁷ functional performance (Short Physical Performance Battery),¹⁸ 4 m gait speed,¹⁹ rectus femoris size (ultrasound of rectus femoris cross-sectional area (Mindray DP-50, Caiyside Imaging, Scotland)), quadriceps strength (isometric QMVC),²⁰ health-related quality of life (King’s Brief Interstitial Lung Disease questionnaire),²¹ activities of daily living (London Chest Activities of Daily Living questionnaire)²² and physical activity parameters (daily step count, time spent sedentary, light and moderate-intensity activity (SenseWear, BodyMedia, USA)).²³

Following the 12-week assessment, purposively sampled participants were invited to take part in semistructured, topic-guided, telephone-based interviews. The audio-recorded interviews explored experiences of the intervention, how it impacted perceptions of outcome, acceptability of outcome measures and trial conduct in order to inform the rationale for and conduct of a definitive trial. The topic guides were updated inductively to reflect experiences and perceptions raised during previous interviews.