For CF, the ANCOVA revealed a significant interaction (P < .001), showing that CF was greater in quartile 4 than quartile 1 in the preintervention evaluation and increased significantly from preintervention to postintervention in both groups with a greater increase in quartile 1 than quartile 4 (an increase of mean [SD] of 22 [14] steps vs 6 [9] steps, P < .001) (Table 3). Here, CFTR is linked to cystic fibrosis.