The goal of a VO2 session is... well I'm not quite sure what the goal of the session is. That's why I have a coach.
How it goes, is that you go flat out for a specified time. Then recover for a specified time. Then go flat out for a specified time, then recover, and repeat for the desired effect.
There are many theories on what the optimal intervals are. Actually, I don't really know, but my coach told me there was. He also told me that the intervals he gave me were the magic numbers, according to research. But I don't really know. That's why I have a coach.
What I do know is how a VO2 interval session goes.
You start your flat out bit. Your legs start hurting. Then your chest starts heaving, to try and get blood to your legs. Then you start gasping for breath, to get try to oxygen into your blood, which is pumping around your body at a frenetic speed.
You try not to think about how hard it is to suck in the breath. Breath, after all, is life. You want breathing to be easy, not hard. Best concentrate on something else.
But what? The possibility that your heart might beat through your chest; or the searing pain coursing through your quadriceps?
After what seems like the longest time, the interval is over and you can recover. For a surprisingly short time.
Then you start again. And that's how VO2 goes.