Effects of Finger Kazoo Exercise With and Without Oropharyngeal Enlargement in the Operatic Singing Voice: A Randomized, Single-Blind, Crossover Controlled Clinical Trial

This clinical trial aimed to evaluate the effects of the semi-occluded vocal tract exercise Finger Kazoo (FK), with and without oropharyngeal expansion, on the singing voice. Fifteen classically trained singers, screened using the Singing Voice Handicap Index-10 (SVHI-10), participated in a randomized, single-blind, crossover trial with two experimental sessions separated by 48 hours. Participants were randomized via Sealed Envelope to start in Condition A (without oropharyngeal expansion) or Condition B (with oropharyngeal expansion). In each session, standardized recordings were obtained before and after the intervention, including maximum phonation time for the vowels /a/ and /i/, and an operatic aria excerpt. Acoustic analysis (PRAAT) extracted fundamental frequency (F0), jitter, and shimmer. Comparisons between baseline and experimental conditions were performed using paired-samples t-tests, Wilcoxon tests, robust paired t-tests, and Friedman ANOVA with Durbin-Conover, Tukey, Bonferroni, and Holm post hoc corrections, with a 95% confidence interval. Auditory-perceptual evaluation was conducted by 15 blinded experts using the EAI Scale Form, with balanced sample distribution among raters. Self-perceptual evaluation was also performed by participants using the same scale.