WS03.05What factors influence heart rate reserve in evaluating and prescribing exercise intensity for children and young people with CF?

Objectives

Heart rate reserve (HRR), the difference between resting heart rate (RHR) and peak heart rate (PHR), is commonly used to evaluate and prescribe exercise intensity in adults (ACSM, 2021). HRR is less commonly used in children and young people (CYP), who are physiologically and metabolically different to adults. They have higher PHR and RHR during rest and exercise and both typically decline with age and fluctuate with changes in physical fitness. This study aimed to investigate the influence of age, fitness and illness on RHR, PHR and HRR in CYP with Cystic Fibrosis (CF).

Methods

Data from CYP with CF participating in Project Fizzyo (UK) were used. RHR was the average of 5 lowest HR values from daily Fitbit monitoring. PHR came from a Polar H10 ECG chest strap worn during a 25-level 10-metre modified shuttle test (MST‐25). Fitness was defined by distance achieved in the MST‐25, normalised for age. Severity of illness was represented by FEV₁ % predicted. Linear regression was used to investigate associations between HRR and age, RHR, PHR, illness and fitness.

Results

134 participants (48.5% male, average age 10.1 years, average FEV₁ 90% predicted) performed the MST‐25 at baseline. Significant associations: Age and fitness explained 41% and 5% of the variability in RHR respectively, with RHR decreasing in older CYP. Fitness and illness explained 14% and 8% of the variability in PHR respectively. The HRR interval ranged between 110 bpm at age 6 to 123 bpm at age 16, increasing by 1.27 bpm (95% CI 0.13 - 2.4) per year, as children got older. PHR explained 46% of the variability in HRR, and PHR, age, fitness and illness combined explained 73% of the variability in HRR.

Conclusion

HRR is strongly associated with age in CYP with CF, and to a lesser degree fitness and illness. While proportional contribution of these factors to HHR may differ in adults, the HRR approach remains appropriate for evaluating and prescribing exercise intensity in CYP with CF.