Immediate effects of a semi-occluded water resistance ventilation mask on objective and subjective vocal outcomes in musical theater students

Background: Traditional semi-occluded vocal tract exercises (SOVTEs) are restricted to single-phoneme tasks due to the semi-occlusion at the mouth, which hinders full articulation, continuous speech, and singing. Innovative SOVTEs should overcome this limitation by creating the semi-occlusion outside the oral cavity. Purpose: The purpose of this study was to investigate the immediate effects of a semi-occluded water resistance ventilation mask, which allows for continuous speech and singing, on objective (voice range, multiparametric voice quality indices) and subjective (auditory-perceptual, self-report) vocal outcomes in musical theater students. Method: A pre-/posttest randomized controlled trial was used. Twenty-four musical theater students (16 women and eight men, with a mean age of 21 years) were randomly assigned into a study group and a control group. The study group received a vocal warm-up session with the innovative water resistance ventilation mask (tube attached to the mask "outside" the mouth), whereas the control group received the traditional water resistance approach (tube "inside" the mouth). Both sessions lasted 30 min and were similar with respect to vocal demand tasks. A multidimensional voice assessment including objective and subjective outcomes was performed pre- and posttraining by an assessor blinded to group allocation. Results: The Dysphonia Severity Index significantly and similarly increased (improved) in both the study and control groups, whereas the Acoustic Voice Quality Index solely decreased (improved) in the control group. The intensity range significantly decreased (worsened) and the semitone range significantly increased (improved) in the study group, whereas no differences in voice range profile were found in the control group. Auditory-perceptually, a more strenuous speaking voice was noticed after the use of the traditional water resistance approach. The subjects perceived both SOVTEs as comfortable vocal warm-up exercises that decrease the amount of effort during speaking and singing, with a slight preference for the water resistance ventilation mask. Conclusions: Both the innovative water resistance ventilation mask and the traditional water resistance exercise seem effective vocal warm-up exercises for musical theater students. The additional articulatory freedom of the mask might increase the phonatory comfort and the practical implementation of SOVTEs in the daily vocal warm-up of (future) elite vocal performers. The hypothesis of a higher transfer to continuous speech or singing in the mask condition has not been supported by the current study. Larger scale investigation and longer term follow-up studies are needed to confirm these preliminary results