Vocal loading

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Vocal loading is the stress inflicted on the speech organs when speaking for long periods.[1][2][3][4][5]



Of the working population, about 15% have professions where their voice is their primary tool.[6] That includes professions such as teachers, sales personnel, actors and singers, and TV and radio reporters. Many of them, especially teachers, suffer from voice-related medical problems. In a larger scope, this involves millions of sick-leave days every year, for example, both in the US and the European Union. Still, research in vocal loading has often been treated as a minor subject.

Voice organ

Voiced speech is produced by air streaming from the lungs through the vocal cords, setting them into an oscillating movement.[7][8] In every oscillation, the vocal folds are closed for a short period of time. When the folds reopen the pressure under the folds is released. These changes in pressure form the waves called (voiced) speech.

Loading on tissue in vocal folds

The fundamental frequency of speech for an average male is around 110 Hz and for an average female around 220 Hz. That means that for voiced sounds the vocal folds will hit together 110 or 220 times a second, respectively. Suppose then that a female is speaking continuously for an hour. Of this time perhaps five minutes is voiced speech. The folds will then hit together more than 30 thousand times an hour. It is intuitively clear that the vocal fold tissue will experience some tiring due to this large number of hits.

Vocal loading also includes other kinds of strain on the speech organs. These include all kinds of muscular strain in the speech organs, similarly as usage of any other muscles will experience strain if used for an extended period of time. However, researchers' largest interest lies in stress exerted on the vocal folds.

Effect of speaking environment

Several studies in vocal loading show that the speaking environment does have a significant impact on vocal loading. Still, the exact details are debated. Most scientists agree on the effect of the following environmental properties:

  • air humidity - dry air increases stress experienced in the vocal folds
  • hydration - dehydration increases effects of stress inflicted on the vocal folds
  • background noise - people tend to speak louder when background noise is present, even when it isn't necessary. Increasing speaking volume increases stress inflicted on the vocal folds
  • pitch - the "normal" speaking style has close to optimal pitch. Using a higher or lower pitch than normal will also increase stress in the speech organs.

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