Exhaling/inhaling?

Normal cardio-respiratory system will produce 35 to 45 mmhg per breath. Your minute volume will adapt to excrete the carbon dioxide. Think about CO2 as the stimulus to breathe, when you exercise you do produce more, so you have to breath either more deeply or more frequently or both to exhale CO2 from your body. That is why it is harder to " hold" or stop your breathing.