During exercise, approximately 25% of inhaled oxygen is consumed, with the remaining 75% exhaled.

“while you are now running and you're breathing you obviously breathing in a certain amount of oxygen into your lungs and then you're consuming some of no or or let's say air into your lungs which contains basically 20.9% oxygen when that comes into your lungs parts of that oxygen far from all of it actually only closer to 25% of that oxygen you are actually actually taking up in your lungs and it's being now transported through your body and you're exhaling actually 75% roughly speaking 75% oxygen you actually exhale out again”