Fat Burning Zone?

Stoshew71

Sorry to the OP for hyjacking his thread. This new stuff interests me.


So I think I kind of understand this RER thing. I guess I didn't realize that oxidation of glucose is done at different ratios on the oxidation of fatty acids.

Oxidation of a molecule of Carbohydrate 6 O2 + C6H12O6=>6 CO2 + 6 H2O + 38 ATP RER = VCO2/VO2 = 6 CO2/6 O2 = 1.0

Oxidation of a molecule of Fatty Acid 23 O2 + C16H32O2=>16 CO2 + 16 H2O + 129 ATP RER = VCO2/VO2 = 16 CO2/23 O2 = 0.7


So you can measure the amount of O2 in the air and compare it to the amount of O2 breathed out to measure the amount of O2 consumed. You can also do the same thing with CO2 to measure the amount of CO2 produced.

Since oxidation of fatty acids has an uneven ratio of O2 consumed to CO2 produced (which I never knew before) and oxidation of glucose has an even ratio of O2 consumed to CO2 produced (as shown by the 2 equations above), then you can estimate the percentage of fatty acids oxidized verses glucose. The closer to a more even ratio suggests more glucose used for energy. The more O2 consumed verses CO2 produced suggests more fatty acids were oxidized.

This would all hold true if we considered complete oxidation of glucose was only used by Krebs and ETC.
However, when intensity levels of exercise being performed that over tax our aerobic system, the equations above are not the only factors involved. In this case, the higher intensity requires more energy that can be supplied by our aerobic system alone. As glycolysis causes at this point only a partial oxidation upon glucose which requires the transformation of pyruvate to lacate and H-ions, glucose is consumed with no additional O2 consumed nor CO2 produced. This alone messes up the equation. Also, since lots of H-ions are being produced due to the anaerobic nature of the fermination of pyruvate, this acidizes the muscle cells which the body initially handles by bicarbonate buffering. This in turn effects the amount of CO2 being produced which further messes up the equation above. The more anaerobic your intensity, the more messed up the equation gets and the RER loses accuracy.

So the moral of the story is around 60-65% maxHR, you can get a very good estimate of what percentage of carbs vs fat is being used as the energy source. But the higher the % of maxHR you go, the less accurate you can estimate fuel source based upon RER alone.

AnvilHead

sijomial wrote: »

...Pet peeve!
Wish people would focus on exercise performance and not the type of fuel used during exercise which is pretty much irrelevant for weight loss/fat loss.

Good point. Some of the science in subsequent posts is interesting from a sports performance standpoint, but the fact remains that substrate utilization/partitioning is not something to be concerned about when considering weight/fat loss. It may be more important to a very lean (say, sub 10%) person trying to become leaner, but for the vast majority of us it's irrelevant.

rontafoya

Since you mention body fat percentage, I'm assuming a lower body fat percentage (leaner body) is your ultimate goal. That said, you will get much better results much quicker--as a male with presumably a typical amount of testosterone for your age--by focusing on heavy compound weight lifting and eating at a 20% caloric deficit. This alone will get you down to about 12-15% body fat pretty quickly. At which point you will likely hit a wall and need to take a break and eat break even for a bit then do the work you need to get down at below 10%. I am 46 and this is working well for me--even easier for you at 22 if you work hard and watch your calories. I won't trash cardio, but I will say it should go from the front of your mind to the back of your mind.

Hornsby

rontafoya wrote: »

Since you mention body fat percentage, I'm assuming a lower body fat percentage (leaner body) is your ultimate goal. That said, you will get much better results much quicker--as a male with presumably a typical amount of testosterone for your age--by focusing on heavy compound weight lifting and eating at a 20% caloric deficit. This alone will get you down to about 12-15% body fat pretty quickly. At which point you will likely hit a wall and need to take a break and eat break even for a bit then do the work you need to get down at below 10%. I am 46 and this is working well for me--even easier for you at 22 if you work hard and watch your calories. I won't trash cardio, but I will say it should go from the front of your mind to the back of your mind.

What does this have to do with the OPs question?

ninerbuff

OP your best bet is to exercise at a level that you can sustain to burn the most calories possible within a given duration.

A.C.E. Certified Personal and Group Fitness Trainer
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Been in fitness for 30 years and have studied kinesiology and nutrition

Stoshew71

Hornsby wrote: »

rontafoya wrote: »

Since you mention body fat percentage, I'm assuming a lower body fat percentage (leaner body) is your ultimate goal. That said, you will get much better results much quicker--as a male with presumably a typical amount of testosterone for your age--by focusing on heavy compound weight lifting and eating at a 20% caloric deficit. This alone will get you down to about 12-15% body fat pretty quickly. At which point you will likely hit a wall and need to take a break and eat break even for a bit then do the work you need to get down at below 10%. I am 46 and this is working well for me--even easier for you at 22 if you work hard and watch your calories. I won't trash cardio, but I will say it should go from the front of your mind to the back of your mind.

What does this have to do with the OPs question?

It doesn't directly. But with all the discussion here, I assume the OP can now realize the myth that these equipment manufacturers create that there is this "fat burning zone" when you perform cardio at a certain intensity (i.e. 60-75% of HRmax) does not equate to, I am going to burn more fat than carbs.

You exercise, you burn calories, period. Those calories can come from carbs, fats, and maybe even proteins. You burn carbs means you are depleting glycogen stores which the body will eventually utilize the food you eat to restore those glycogen stores. (unless you have an extreme low carb diet i.e. Keto or Atkins). I believe the OP stated that they are following a low carb diet but not sure if they are following an extreme low carb.

But the body can produce glycogen from other food sources other than carbs. I do not follow a low carb diet, but from my reading, I understand that performance in your workout drops when you are not fully carb loaded. However, I heard many individuals on low carb swear they feel better on low carb after the flu stage subsides.

But all of that doesn't matter unless you factor in net calories comsumed through your diet.

At 23.4% body fat, I would consider that normal or moderate level (the OP is not extremely obese or overweight).
I assume they are considering ways to use cardio in addition to his strength training to drop an even lower BF% and he came accross this "fat burning zone" on the treadmill and wanted to get everytone's take on it.

I haven't seen one person on this thread actually suggest that "fat burning zone" was a positive thing and suggested other alternative ways to drop to a lower BF%. For example, compound exercises, eat at a calorie deficit.
Bottom line, (to quote a couple of people on this thread) eat at a calorie deficit and focus on exercise performance and not the type of fuel used during exercise.

I personally am no longer worried about my BF% and I stopped trying to lose weight over a year ago. I am now at the stage where I am trying to improve my performance in running. That is where my focus on a lot of these discussions are. But when i was loosing weight, I did a mixture of weights and running combined with using mfp to track my calories very carefully and used the calorie deficit that mfp suggested. I dropped about 45 pounds in about 6 months from Oct 2013 to March 2014. I lost maybe another 5 pounds since then by increasing my running mileage for marathon training. I am trying to just maintain as I don't want to gain or lose anymore. Performace and improving my marathon pace is where I am at now.