| Study design | Exploratory pilot study; mixed design with between-subjects factor (cheek condition) and within-subjects factor (time). Between-condition comparisons were interpreted as preliminary due to the small group size. |
| Participants | 11 healthy adults recruited; 8 participants with complete pre–post data included in final analysis |
| Inclusion criteria | Age ≥ 19 years; no self-reported voice disorders; ability to follow experimental instructions |
| Exclusion criteria | Voice disorder diagnosis or treatment within 6 months; respiratory illness or upper airway infection; neurological conditions affecting phonation or respiration; incomplete pre–post measurement data |
| Group allocation | Cheek Inflation group (n=4); No Cheek Inflation group (n=4) |
| Intervention task | Straw phonation tasks consisting of sustained /u/ phonation, pitch ascending and descending tasks, ascending and descending glissando tasks, and one set of the “Happy Birthday” melody; Cheek Inflation: cheeks maintained in an expanded state; No Cheek Inflation: cheeks kept unexpanded during the same tasks |
| Measurement timing | Pre, before straw phonation; Post, immediately after straw phonation |
| Outcome domains | Aerodynamic measures as primary exploratory outcomes; acoustic measures as secondary exploratory outcomes; GRBAS as a descriptive reference measure |
| Acoustic measures | RTP: habitual pitch (F0); MDVP: F0, jitter (%), shimmer (%), NHR; ADSV: CPP (dB), L/H ratio |
| Perceptual measures | GRBAS (G, R, B, A, S), used to characterize the auditory-perceptual status of healthy participants |
| Aerodynamic measures (primary) | PAS: AP, PAP, EAD, PEA, PT, MPAP, MADV, AE, MSDV, EV, MEA, AR |
| Statistical analysis | Nonparametric methods; Wilcoxon signed-rank test for pre–post comparisons; Mann–Whitney U test for between-group delta comparisons; effect sizes: rank-biserial correlation (r), Cliff’s delta; descriptive statistics: median (IQR); p-values interpreted descriptively due to the exploratory small-sample design; no correction for multiple comparisons |