RESUMO
Importance: External vibration therapy (EVT) has been widely used in chronic pain conditions, musculoskeletal rehabilitation, and athletic training. Vibration therapy has been suggested to enhance vocal performance and has been popularized in social media. However, there is no evidence to support its effect on vocal function. Objective: To evaluate the immediate effects of EVT in trained singers using acoustic and self-assessment parameters. Design, Setting, and Participants: Prospective, randomized, placebo-controlled interventional study at St Michael's Hospital Voice Clinic, affiliated with the University of Toronto. Data collection and analysis were performed by investigators who were blinded to the group assignment of the participants. Study participants were randomized to EVT or a placebo (control) group. The study dates were September 2015 to December 2016. Interventions: Participants attended the voice laboratory at St Michael's Hospital, where a standardized data collection protocol was performed, including acoustic parameters, voice range profile, and soft voice tasks, followed by subjective rating of vocal effort or discomfort. The EVT group underwent EVT to 5 neck sites bilaterally. The placebo group underwent the same protocol with a modified device. After the intervention, the participants repeated the standardized data collection. Main Outcomes and Measures: The primary outcome in this study was acoustic analysis (jitter, shimmer, and pitch range) compared before and after treatment. In addition, secondary outcomes included perceived effort or discomfort evaluated by participants after 4 voice tasks proposed to investigate more subtle voice properties. Within and between groups, data sets were statistically analyzed for potential treatment effect. Results: Among 27 participants (age range, 18-50 years; all female), 14 were randomized to the intervention group and 13 to the placebo group. Comparison of the treatment effect on the vowel token acoustic parameters evaluated showed that, after EVT, participants had a more cohesive change with a restricted 95% CI compared with placebo. The mean change in fundamental frequency after intervention was 5.00 Hz in both groups but the 95% CI was much wider after placebo (-30.30 to 19.20) than after EVT (-18.10 to 7.50). After EVT, the effect size was notable in the vowel (0.83) and SVT3 (0.79) task. Conclusions and Relevance: In this study, EVT demonstrated a more predictable change in acoustic metrics compared with the placebo treatment. Effort ratings for 6 voice tasks evaluated in this study were not found to be different after EVT compared with the placebo treatment. Trial Registration: clinicaltrials.gov Identifier: NCT02083341.