It is not the lung capacity, the force and the volume of air that is important in speech and singing. Rather it is the control of the air. It is air passing over the vocal cords on the out-breath that makes the ‘voice’ and only a little air is needed to set them vibrating. The less breath you use, the better the tone. The key then is to be an efficient breather.
Australian opera singer Dame Nellie Melba wrote in her book The Melba Method, “if only a little breath is necessary, it is obviously wise not to take too much air into the lungs”. The American singer Frank Sinatra had breath control that was legendary. You could not hear him take a breath, and it was hard to see it happen.
I have worked with many professional speakers, actors and singers and invariably if they were having stage fright, voice projection or vocal strain and vocal fatigue issues, they were dysfunctional breathers.
With breathing retraining improvement is usually evident within 24 hours. As it was with Madeline. She was a museum guide, and used to cough constantly throughout her tours. Not only did her cough stop as soon as she started breathing retraining but she found she no longer got exhausted from talking all day, did not have to clear mucous from her throat and did not get dehydrated like she used to.
The best strategy to adopt right now to take the strain off your voice is to treat your airways gently. Breathe gently, speak gently. Learn to breathe correctly.
(And cease practice of full-lung volume and forceful exhalation exercises unless a health practitioner has a scientific explanation for why you should do so.)