Consider someone who is speaking in a loud voice or who is speaking continuously for a long period of time. First, in preparation for speaking, the person takes a deep breath using thoracic or abdominal breathing. When speaking, breath is exhaled through the narrow opening of the glottis while causing the vocal cords to vibrate. At this time, the exhalation force is mainly supplied by the contraction of the abdominal muscles. Why is abdominal breathing recommended for speaking? Abdominal breathing is the natural choice, first because it is possible to inhale and exhale a larger amount of air with abdominal breathing than with thoracic breathing, and second because it is primarily the abdominal muscles that control the force with which breath is exhaled while talking.
- T. Arai and T. Arai, “Virtual lung model for education in phonetics and speech science,” Acoust. Sci. Tech., 37(4), 173–174, 2016.