Clinical relevance of maximum phonation time in children and adolescents: Task-dependent roles of age, sex, and forced vital capacity.

This study examined whether spirometrically measured forced vital capacity (FVC) is associated with one-breath endurance in typically developing children and adolescents, and whether this association differs by task. A total of 971 participants aged 8-17 years completed sustained /a/ and repeated /ka/ to exhaustion after maximal inspiration. FVC was measured concurrently by spirometry. A unified long-format regression model showed that endurance was longer for sustained /a/ than for repeated /ka/, and that age and FVC significantly predicted performance in both tasks. However, the FVC - endurance association was stronger for sustained /a/ than for repeated /ka/, whereas age effects were larger for repeated /ka/. No adjusted sex difference was observed for sustained /a/, whereas females showed longer repeated /ka/ endurance despite smaller FVC. Age- and sex-stratified values and capacity-adjusted residual flags support task-specific interpretation of one-breath endurance and may improve clinical interpretation of paediatric speech-breathing function. By separating respiratory capacity from task-specific endurance, this approach may help clinicians distinguish predominantly capacity-limited from coordination-limited patterns of reduced speech-breathing endurance.