The common idea in pre-contest training and dieting is that aerobic activity (traditional cardio) is added to enhance fat burning and increase or raise metabolism. What aerobic training does is make a person more “efficient” at using fat as an energy source. While that sounds great on the surface, it’s actually opposite of what you are trying to do. To be more efficient means it starts using fat slower and better to fuel the activity. To be more “efficient” at using fat as an energy source means it burns less of it, not more of it! Other than the calories burned during activity, there is no up regulation benefits of metabolism from aerobic activity!
So all these physique athletes doing all this excess aerobic volume of up to 2 hours per day are actually programming their bodies to not only use less fat, but to store it better as well. There is also a huge down regulation mechanism of metabolism with aerobic work. The dieting body responds to a lack of calories and excess aerobic training by slowing metabolism and signaling for more enhanced fat storage. At the same time there is also muscle loss because of the need for fuel from muscle. For those individuals doing extreme diets on top of their training, this enhances the metabolic shutdown. The result is devastating to competitors during contest prep by trainers who end up prescribing more of the same when weight loss plateaus, thereby practically guaranteeing a post-contest fat rebound, Because you programmed your body to do so.
So if you are doing 2+ hours of cardio per day to get ready for a contest you may want to think twice if you want to avoid possible metabolic issues. Will it happen to everyone, No. Can it happen to most, Absolutely. If you are doing 2 hours of cardio a day to lose fat then you are either getting bad advice, over-dieting, or you just are not made to compete and get your body down to the required body fat levels. This sport isn’t for everyone, but that doesn’t mean you can’t develop a great physique in a healthy manner.
One last thing is that some aerobic cardio is fine and maybe needed, I even it prescribe it to some clients, but we only use it when needed and never do more than 45 min at a time. It’s a good tool if applied properly and in this case more isn’t always better.