The relationship between exercise intensity (% of your Maximum Heart Rate) and the energy source (carbohydrate and fat) is as follows:

% MHR__% Carbo__% Fat
65 to 70____40______60
70 to 75____50______50
75 to 80____65______35
80 to 85____80______20
85 to 90____90______10
90 to 95____95______5
100_______100______0


I didn't realise at low heart rates that the body was burning 40% carbs. I always thought at low heart rates the body was burning fat almost entirely. This suggests in ketosis, where the body has no glycogen stores, that the body cannot function at upper heart rates. It explains why my ability to run suffers if I don't have carbohydrates on board.

When in college I studied 'Feeds & Feeding'. Since I was a weightlifter, swimmer and long distance cyclist at the time I easily translated the information I got in that class into what I was trying to accomplish in my exercising.

I was also raising out a batch of yearling ewe lambs at the time and in my inexperience bred them too early in their lives. It was the biggest lesson in protein catabolism I ever got...

The trick to all of this is 2 fold:

1) The body needs to be trained to burn fat for it's NRG needs. For the average everyday person just doing some form of exercise, their bodies need to be trained starting in the 'Fat Burning' zone (60-70%) and slowly brought up to the 'Aerobic' and possibly 'Anaerobic' zones. (Just like a cyclist that is coming back from an extended break. The first thing they need to do is work on rebuilding the capaillaries in their legs for maximum muscle oxygenation during riding. That's best done by simple walking exercises.)

2) Replace the protein used for NRG within the first half hour after training, which is when the body is most able to rebuild that type of damage. The caveat to this is that it needs to be a bioavaiable protein to be of most value.

Tables are nice, but sometimes the data does not apply.

The percentage of energy from fat varies not only with intensity of exercise but with amount of training and diet composition.

Get a copy of "The regulation of carbohydrate and fat metabolism during and after exercise." by John O. Holloszy, Wendy M. Kohrt and Polly A. Hansen of the Department of Medicine, Washington University School of Medicine; abstract here.

Figure 1 in the paper shows the difference in fat burning percentage between untrained individuals and endurance trained people. The trained peoples glucose percentage is 10 to 15% lower at any given intensity.

Figure 2 shows the difference in fat burning percentage between those on a high carb diet and those on a high fat diet. The high carbers show increasing glucose requirement as the intensity of exercise increases. (approximately 70% carb oxidation at 70% V02Max). The high fat dieters shows a constant carb oxidation percentage at all levels of exercise. That level is only 40%.

According to the paper

In the paper "Fat utilization during exercise: adaptation to a fat-rich diet increases utilization of plasma fatty acids and very low density lipoprotein-triacylglycerol in humans" the conclusion is

As most exercise data has been taken on high carb eaters, it is misleading to apply the results to low carbers.

This appears to be the only real difference in what we're each saying...But, once again, the body needs to be trained for it...

The "burning a higher percentage of fat" = "burning more fat overall" equivalence seems to be a pretty persistent fallacy. While it is certainly true and amply demonstrated that our bodies burn more fat (as a percentage of total calories) at a lower intensity than at a very high intensity, people don't seem to take into account the fact that you just plain burn more calories at higher intensities. Essentially, it comes down to exercising in the most efficient manner.

For example (and I'm not trying to pick on you, locarbbarb, this is a topic that trips up tons of people):



If you spent that sixty minutes at a high intensity, you would burn 400 calories; 50 percent of that would be bodyfat, so you would burn 200 calories' worth of body fat.

In other words, you could get the same benefit of the low-intensity 60 minutes in about 45 minutes -- except not only would you have burned the same amount of fat, you would also have burned about 1.5 times the calories.

Now, in terms of effectivity, cardio interval training seems to be the best: Tremblay's 1994 study on interval training (Tremblay et al; Metabolism 43: 814-818 (1994)), showed that small amounts of interval training were greatly superior in terms of fat loss to much longer periods of low-intensity cardio — up to nine times more effective at reducing subcutaneous body fat. Cardio interval training is basically just running (or whatever) at a very high intensity for a short period of time (anywhere from ten seconds to a minute), then walking for a couple of minutes until you're pretty close to fully recovered, then running again.

Unfortunately, I don't have any information on how any of this changes with a fat-burning metabolism; I will leave that up to the other amply capable hands in this thread.

My guess is the short bouts of extreme exercise stimulates Growth Hormone, which acts like an anabolic steroid. Another theory is that myglobin, which stores oxygen, is depleted rapidly and oxidizes fat to replenish. I got that from Body For Life.

What is a bioavaiable protien? Do you have examples?

I like the advice I read in the book "younger next year", something along these lines:

level one (beginners) work up to 45 minutes a day, six days a week, low intensity aerobic exercise

level two (after a few months of level one, how long depends on your condition, age, inclination, etc) - , low intensity aerobics 4 days a week, weight training, two days a week.

level three - do low intensity aerobics 2 days a week, mix in high intensity anaerobic tranining 2 days a week (working at a higher effort level, 70 to 80% of your max I think, adding some sprint work in there as well - hitting it all out for some short spurts. Wt. training 2 - 3 days a week.

the most important thing, btw, probably far more important than your effort level, is that you do it six days a week, without fail.

the big idea behind all of this is to reverse your bodies natural inclination to decay (after a certain age) with various chemicals that send growth signals to your body... the book goes way more into detail, of course, that's just my quickie thumbnail version...

Do interval workouts 2-3 times a week (get around your 85% MHR threshold) and do a medium intesty level workout 2-3 time a week.