Speech is nothing but a controlled outward Breath.
Diaphragm controls how the breath and how the voice flows. Under stress and anxiety, the Hypothalamus of our brain triggers and activates the pituitary gland to release ACTH. ACTH hormone stimulates the Adrenal glands and this initiates flow of Adrenalin (a hormone) to blood.
Enhanced levels of Adrenalin, can trigger the fight-flight mechanism; shallow chest breathing, increased heart rate and can make a person feel suffocated in the ‘gut’ (the diaphragm) resulting in voice coming out weak.
Controlling the breath for public purposes is similar to performing breathing exercises and speech is nothing but controlled outward breath.
Breath is language. Every thought and every emotion can be detected in the breath. When you get agitated, mentally or physically, feel fear, anger or sadness, rhythm of the breath synergises with the emotion.
Ideally, Breath comes back to its natural state but due to gating; energy, both emotional and physical, stays locked-in in the system and gets accumulated over a period of time.
Unless processed, this energy manifests as aura and is visible to people around.
The diaphragm is known to store all of this ‘gated’ energy. Sine Wave Breathing helps ungating the energy.