You sometimes hear you should do cardio on empty stomach, because it supposedly burns more fat. Why is this wrong and especially harmful for athletes?
When you do it in fasted stated, more of the energy you use during cardio will indeed have to come from fat. But you will burn fewer calories - and therefore also less fat - in total!
This is because to perform well during cardio, you need some carbohydrates in your system, as carbohydrates allow you to put out a lot of power at once. Fat in comparison takes ages. Less performance = fewer calories burned.
Less Training Effect
And because you most likely won't be able to perform very well, you will also receive less training effect from your cardio sessions. That is very bad for athletes who rely on putting out their best performance in competitions: