Doing short bursts of intense exercise a few times a week for 12 weeks makes people with excess body fat able to exercise longer before getting tired, but doesn't significantly improve their maximum oxygen capacity.

Doing short bursts of intense exercise for 12 weeks doesn't improve the maximum oxygen your body can use during exercise in people with excess body fat, even though they can exercise longer before getting tired.

Eating very few carbs and more fats for 12 weeks doesn't improve the maximum oxygen your body can use during exercise in people with excess body fat when measured in absolute terms.