Video-Based Lessac-Madsen Resonant Voice Therapy: Short-Term Effects on Phonation in Japanese University Students

Background: Lessac-Madsen Resonant Voice Therapy (LMRVT) was originally developed for individuals with vocal disorders to promote phonation with reduced strain on articulation-related muscles and vocal cords by emphasizing resonance in the front of the face. This study hypothesizes that LMRVT can also enhance phonation efficiency in healthy individuals. Given the limited research on its applicability to non-disordered populations, we investigated the short-term effects of LMRVT on adults without vocal disorders using a single 30-minute instructional video session. Methods: 39 Japanese female university students participated in a body-relaxation exercise and phonation practice involving humming on /m/ while watching the instructional video. The therapeutic effect was assessed by measuring the difference in maximum phonation time (MPT) before and after the session. Additionally, we examined the relationship between MPT outcomes and acoustic characteristics of five sustained vowel phonations. Acoustic parameters included vocal space area (VSA) and the difference between the first and second harmonic amplitude (H1-H2). Results: MPT significantly increased post-intervention (Wilcoxon test, p<0.05). MPT improvement was positively correlated with VSA (Spearman`s ρ=0.58, p<0.001) and negatively correlated with H1-H2 for vowels /u/, /o/, and /e/ (ρ=-0.50, ρ=-0.47, ρ=-0.39, p<0.05, respectively). These results suggest that even a single short session can facilitate easier phonation, leading to prolonged phonation time. However, 14 out of 39 participants did not exhibit MPT improvement, indicating that repeated exercises may be necessary for those struggling to adopt a new phonation style. The observed VSA expansion suggests enhanced articulatory relaxation, potentially increasing tongue movement range and altering formant frequencies. The reduction in H1-H2 post-therapy implies a shift toward relaxed phoation, characterized by a steeper spectral tilt in the laryngeal source spectrum. Conclusion: The findings suggest that short-term LMRVT intervention can improve phonation efficiency, potentially contributing to the prevention of vocal fold overuse and disorders while maintaining vowel intelligibility through increased VSA. These results highlight the potential benefits of LMRVT for healthy individuals as a preventative and training tool. Further research is needed to explore the long-term effects, efficacy of repeated LMRVT training, and its impact on speakers with varying vocal demands.