(271) Impact of habitual levels of moderate to vigorous physical activity on FEV₁ in children and young people with cystic fibrosis: Results from Project Fizzyo

Background: All children and young people (CYP) aged 5-18 years, including CYP with CF (CYPwCF) are recommended at least 60 minutes of moderate-to-vigorous intensity physical activity (MVPA) each day [1]. However, not all CYPwCF undertake regular MVPA and little is known about the impact of different habitual levels of MVPA on lung function over time.

Methods: Project Fizzyo was a longitudinal observational study which included objective measures of daily habitual MVPA over 16 months in CYPwCF aged 6-16 years [2]. All participants were given a Fitbit Alta HR activity tracker which continuously captured raw heartrate (HR) data. A personalized MVPA threshold for each CYPwCF was calculated using their own peak HR (PHR) and resting HR (RHR) data. Time in MVPA was defined as the sum of minutes per week (min/week) in which the average HR from any activity exceeded the personalized MVPA threshold: (PHR - RHR) x 0.4 + RHR [3].

MVPA data were reconciled with longitudinal clinical data for each CYPwCF and individualized polynomial regressions for FEV₁ %predicted were used to match the time intervals of MVPA data. A linear mixed effects model was used to estimate the effect of habitual MVPA in min/week on FEV₁, accounting for disease severity, age, number of intravenous antibiotics and use of modulator therapies.

Results: 145 CYPwCF contributed 30,926 days of HR data from 3 UK CF centres. Personalized HR thresholds for MVPA ranged between 110–130 beats per minute. Total MVPA < 25 min/week was not associated with any FEV₁ benefit. Total MVPA between 25-150 min/week produced significant but modest benefits in FEV₁ (< 3% predicted extrapolated over one year), whereas MVPA >150 min/week produced significant and clinically important benefits in FEV₁ ( >5% predicted extrapolated over one year). In our population, 32 CYPwCF (22%) produced no weeks with MVPA >150 mins, while 15 CYPwCF (10.3%) were responsible for 40% of the 1552 weeks recorded with MVPA >150 min/week (Fig 1A). This minority of very active individuals recorded MVPA >150min/week in at least half of the 64 weeks’ duration of the study

Conclusions: Results suggest that even after adjusting for disease severity, age, antibiotics and modulator therapies, habitual levels of MVPA can have an important impact on lung function in CYPwCF, who might expect to accrue significant gains in health from regular habitual MVPA exceeding 150mins/week. This threshold for benefit is much lower than the 60 min/day (420min/week) of exercise recommended. However, there are still too few CYPwCF achieving this threshold regularly and these findings may provide a focus for enabling more people to experience benefits from regular MVPA.

Acknowledgements: Supported by UCL Rosetrees Stoneygate prize (M712), CF Trust Award (CEA010), UCL Partners and HEFCE Higher Education Innovation Fund (KEI2017-01-04) and NIHR GOSH BRC.

References:

1. Chaput JP, Willumsen J, et al. 2020 WHO guidelines on physical activity and sedentary behaviour for children and adolescents aged 5-17 years: summary of the evidence. Int J Behav Nutr Phys Act. 2020;17(1):141. doi:10.1186/s12966-020-01037-z


2. Raywood, E., H. Douglas, E. Main.et al. 2020. 'Protocol for Project Fizzyo, an analytic longitudinal observational cohort study of physiotherapy for children and young people with cystic fibrosis, with interrupted time-series design', BMJ Open, 10: 10, e039587. doi:10.1136/bmjopen-2020-039587


3. AMERICAN COLLEGE OF SPORTS MEDICINE 2014. ACSM's Guidelines for exercise testing and prescription, Baltimore, Lippincott Williams & Wilkins.