Cardio vs. fat burning

[foxriver]

Ok, my mother is a science teacher for middle school. And she had the nerve to ask this question, and then she started to use all sorts of scientific reasoning why one was better than the other. Then I did a google search to find an easy answer and still got two conflicting answers. Apparently this is a debatable subject, and I'd like to know, scientifically, why a 26 year old doing cardio at about 160 bpm rather than 130 bpm assuming consistant effort and same duration will not burn more fat than someone at the 130 bpm heartrate. One of the '"personal trainers" at the gym said that the simple answer is that higher heartrate burns muscle, which is bad. And if that is true, I agree, but it doesn't explain why cardio doesn't burn more fat than the "fat burning" heartrates.

Basically from all that I have read, it seems the simple answer that doing fat burning range for heartrate for people that want to lose fat, is the lesser of two evils since you will still burn fat, but not at the risk of losing muscle mass.

Then again, I've also read people disagreeing that cario catabolizes muscle at all.

Can anyone shed some medical light on this subject? If you could explain why you think that way as well, such as having a PHD in something, or work in a fitness lab or whatever your credentials, that will help me convince my mother that the answer I have come up with is the general consensus. We both agree though that the subject is controversial and that there is no exact answer. ( I don't want you to think that it is just an argument about who is right.)

 

[Protobuilder]

If I understand your question, it's pretty simple really. The body burns different fuels at different heart rates. While you're sitting here surfing the internet, your body is using glycogen (I believe, don't quote me) to run its organs. Your brain uses a lot of energy. And your muscles aren't using much energy at all. As your heart rate increases, into the "fat burning zone" (which is a whole diff't debate), your body draws on its adipose stores (fat . . .process is lipolysis, i think). As you go higher up the scale, into higher intensity cardio (think, fast jog or hard sprints), your body starts burning glycogen from the muscles and liver. If you push really really hard, or your body runs out of other fuels, your body will convert proteins into energy. This doesn't happen easily, as I understand it. Overall though, that's it. Now, it's not that clean: you probably burn fat & glycogen at the same time to some extent, but at different ends of the spectrum, you'll burn more of one fuel than the other.

So, that's why lower intensity cardio burns more fat than high intensity cardio.

The bigger debate though is, does it matter for fat loss? I say no. But that's a diff't debate.

If you enjoy this type of egghead wanking, you might read the articles at abcbodybuilding.com

Also, just a little bit on what I mentioned above: http://www.unu.edu/unupress/food2/UID07E/uid07e0x.htm#4. substrate metabolism in exercise

My credentials? I've read lots & lots of smart people, PhDs and all. LoL