Background: The six-minute walk test (6MWT) is used to assess functional capacity in primary ciliary dyskinesia (PCD). We aimed to investigate the clinical determinants of the 6MWT in PCD.

Methods: Thirty-six PCD patients (mean age=13.46±3.33 years, 20F, forced expiratory volume in one second, FEV1=74.64±12.13%) were included. Respiratory muscle strength (maximal inspiratory pressure, MIP, and maximal expiratory pressure, MEP, respectively), quadriceps muscle strength, (QMS), dynamic balance (Y balance test, Y-BT), and functional capacity (6MWT) were assessed.

Results: 6MWD was significantly correlated with z score of height (r=0.376, p=0.024), FEV₁ (%) (r=0.334, p=0.046), MIP (r=0.502, p=0.002), QMS (r=0.416, p=0.012), anterior Y-BT score (r=0.479, p=0.003), and posterolateral Y-BT score (r=0.645, p<0.001). The MIP explained 38% of the variance in 6MWD distance (r=0.617, r²=0.380 F(1-34)=20.867, p<0.001).

Conclusion:  Exercise capacity is related to height, FEV₁, MIP, QMS, and balance in patients with PCD. Inspiratory muscle strength is an independent determinant of 6MWT distance in PCD. Considering that the MIP is independently associated with the 6MWT distance, it may substantially impact functional capacity in patients with PCD. These findings should be considered for comprehensive assessments and further interpretations of functional capacity in patients with PCD.