Peripheral Muscle Function and Body Composition in People With Cystic Fibrosis on Elexacaftor/Tezacaftor/Ivacaftor: A Cross-Sectional Single-Centre Study.

Background: People with cystic fibrosis (pwCF) often have multifactorial peripheral muscle abnormalities attributed to, for example, malnutrition, steroid use, altered redox balance and, potentially, CF-specific intrinsic alterations. Malnutrition in CF now includes an increasing prevalence of overweight and obesity, particularly in those receiving CF transmembrane conductance regulator (CFTR) modulator therapy (CFTRm). We aimed to characterise peripheral muscle function and body composition in pwCF on Elexacaftor/Tezacaftor/Ivacaftor (ETI) CFTRm, compared to healthy controls.

Methods: Fifteen pwCF on ETI, and 15 healthy age- and sex-matched controls (CON), underwent whole-body dual-energy X-ray absorptiometry scans, and a comprehensive evaluation of peripheral muscle function. Tests included quadriceps maximal isometric force measurement, an intermittent isometric quadriceps fatiguing protocol, handgrip strength dynamometry, squat jump height assessment, and 1-min sit-to-stand testing.

Results: No significant differences in quadriceps maximal isometric force (CON: 181.60 ± 92.90 Nm vs. CF: 146.15 ± 52.48 Nm, p = 0.21, d = 0.47), handgrip strength (CON: 34 ± 15 kg vs. CF: 31 ± 11 kg, p = 0.62, d = 0.18), peripheral muscle endurance, fatigue, or power were observed between the groups. Moreover, no significant differences in whole-body, trunk or limb lean mass, fat-free mass, fat mass, or whole-body bone mineral density were evident.

Conclusion: Comparable peripheral muscle mass and function has been demonstrated in pwCF on ETI, albeit a group with good lung function. Research is needed to confirm these findings longitudinally in pwCF, including those with more severe lung disease, who are less physically active, and have less optimal nutrition and exercise support.