Response to letter to the editor re ‘Relationship between exercise test performance and lung function in CF’

We would like to sincerely thank Mosadeseh Sani and Erfan Ayubi for the interest in our paper [1]. The main aim of this study was to investigate the relationship between lung function and exercise performance in adults with CF. We feel that our study elegantly shows the non-linear relationship between lung function and distance walked after performing the incremental shuttle test (MST).

Our secondary aim was to develop a CF-specific equation to predict MST performance. The multivariate regression analysis showed that in patients with FEV1 <67%, males walked approximately 280 m further than females; with every additional year of age, patients walked 9 m less; and with every 1% decrease in lung function, patients walked 15 m less. We think this delivers important clinical and useful information for physiotherapists working with adults with CF. We acknowledge the comment of the authors about cross-validation and invite these and other researchers to cross-validate our regression equation in another sample of CF patients.