I don't know when people will realize this, but having excellent cardio is part hard work, and MOSTLY A GIFT.
You can train something all you want, but it only comes out if you actually have it in you.
I would bet there are a thousand fighters in the USA who train cardio as hard as Frankie Edgar does, but nearly every single one of them will never be able to keep Frankie's pace for 25 minutes. That is because Frankie is more gifted.
Since Overeem doesn't have that gift, his best bet is to try to take care of business in the first 3 minutes. That was a major blunder to fight Bigfoot the way he did; I had a bad feeling for him when the horn sounded signaling the end of R2.
He wouldn't admit it, but he gassed against Werdum and almost got caught in a heel hook at the end. He might have lost that fight if there was another round, even though Werdum's cardio is nothing special.