Vocal change patterns during a teaching day: Inter- and intra-subject variability

Objectives: To describe the mean voice changes of 22 female teachers during a typical workday, examine the inter- and intra-subject variability, and establish a typology of different voice patterns during the workday.
Methods: For each participant, fundamental frequency (F0), harmonics-to-noise ratio (HNR), jitter, and shimmer were measured on sustained vowels at the beginning and at the end of the workday, at three different times during the school year.
Results: The group mean pattern showed significant increases in F0 and HNR during the workday and significant decreases in jitter and shimmer. However, considerable inter- and intra-subject variability was observed. Based on the variation in the acoustic parameters during the workday, three different voice patterns were identified. The first is characterized by a greater F0 increase during the day, interpreted as a common, appropriate adaptation to vocal load. The second is characterized by a greater increase in HNR during the day and greater decreases in jitter and shimmer, interpreted as hyperfunctional voice production. The third is characterized by greater decreases in F0 and HNR and greater increases in jitter and shimmer, suggesting acute inflammation or muscle fatigue following the workday.
Conclusions: The observed variety of vocal patterns during the workday emphasizes the need to study this phenomenon individually and target different types of behaviors in order to develop tailored prevention and treatment methods.