How does your posture affect voice and speaking? How does breathing affect voice and speaking? Do they have an impact?
I can’t think of any things that breathing and posture don’t affect!
Your breath is what causes your vocal cords to vibrate; your ability to pace a fine, continuous stream of air through the cords as you exhale determines the quality of the vibration, the amount of pressure on the voice, and the energetic impact of your voice on yourself and others.
If your posture is not aligned, your ability to manage the breath, vibrate the vocal cords precisely, resonate fully and articulate will all be compromised.
That being said, people with physical handicaps that cause postural and breathing limitations still manage to develop effective and beautiful vocal expression. In these cases it is the soul’s deep desire to express that triumphs.