Does Water Resistance Therapy Influence Vocal Vibrato In Classically Trained Singers?

Water resistance therapy (WRT) exercises are a common tool that aims to relax and free the voice by increased impedance and the massage effects of pressure modulations of low-frequency bubbles. It has been hypothesized that such exercises could have a direct effect on vocal vibrato due to relaxation effects or sensorimotor feedback loops. Since the bubbling frequency is often slightly faster than vibrato in trained singers, it has been hypothesized that vibrato rate could be increased after WRT. To assess this topic, the phonations of eight Western-classically trained singers (three male, five female) with intended vocal non-vibrato and vibrato were recorded through simultaneous high-speed videolaryngoscopy (20,000 fps), electroglottography (EGG), audio recordings, and a Rothenberg mask. The task of sustained phonations on vowel [i] was performed before and after a 10-minute water resistance exercise, as well as 10 minutes later. Calculated outcome parameters were Vibrato Extent (VE), Vibrato Rate (VR), their Coefficients of Variation (CV), Sound Pressure Level (SPL), Cepstral Peak Prominence (CPP), Open Quotients, Closing Quotient and Nasalance. The level for statistical significance was set to α = 0.05 and adjusted to α_adj = 0.0167 due to Bonferroni correction for multiple comparisons. VE showed a tendency of decrease (P = 0.019), and CPP was found to be significantly raised (P = 0.003) directly after WRT. The other parameters did not reach statistical significance. In seven cases, nasalance varied at the same rate as the vibrato, possibly either due to an acoustic compliance of the soft palate during phonation or a physiological chain reaction to vertical larynx movements associated with vibrato. This observation was independent of the WRT. It is concluded that WRT does not influence vibrato parameters to a great amount in trained singers.