I have spoken for 55 minutes straight and if I had spoken 10 more minutes, I would have lost my voice. My mouth had started to produce a lot of saliva, my lips were desiccating and my brain got tired of processing the numbers and words on the pages. This can only be improved by training my brain and my mouth to speak and bear the test of time and pressure. I shall work on my cardio and overall physical health to improve my vocal skills. Joe Rogan speaks enthusiastically for 3-4 hours without breaking a sweat, I want to reach that state of performance.