Fat oxidization (burn) vs. Muscle glycogen & triglyceride burn

[studen77]

http://www.bioscience.org/1998/v3/d/holloszy/4.htm



Maybe some of you have already read this, but I found it a VERY good research publication by Washington University School of Medicine on the rate of fat burn vs. muscle glycogen & muscle triglyceride (muscle burn) in relation to the intensity and duration of exercise.



Here's some quotes:

While the absolute work rate determines the total quantity of fuel required by the muscles during exercise, the relative exercise intensity is a major factor in determining the fuel mixture, i.e. the proportions of carbohydrate and fat, oxidized by the working muscles (27,68). During exercise performed after an overnight fast, 70-90% of the energy required at low exercise intensities in the range of ~25-30% of VO2max is supplied by the oxidation of fat. As shown in figure 1, as relative exercise intensity is increased from ~40% to ~85% of VO2max, there is a decrease in the percentage of the total energy requirement derived from fat oxidation and a reciprocal increase in carbohydrate oxidation.

Here's a chart they composed to illustrate the studies:

So basically what they found is that after an overnight fast, excercise done immediately before any food intake at low intensity (25-30% of VO2max (and I think VO2max is related to MHR??)

the majority of energy burned will come from fat and fatty acids, versus high intensity where most of the energy will come from carbohydrates.



THey also state that:

During moderate intensity exercise, in the range of 55% to 75% of VO2max, that can be maintained for 90 minutes or longer, there is a progressive decline in the proportion of energy derived from muscle glycogen and muscle triglycerides, and a progressive increase in plasma fatty acid oxidation (27). During the first 30 minutes or so of moderate intensity exercise in the fasting state, plasma fatty acids and muscle triglycerides provide roughly equal amounts of the fat that is oxidized. When the exercise is continued beyond 30 minutes, oxidation of plasma fatty acids provides progressively more of the total energy requirements, compensating for the decreased utilization not only of muscle triglycerides but also of muscle glycogen (27).

So after 30 min of exercise the rate of "muscle burn" decreases and a higher reliance of fat and fatty acids was documented.





So in summary, I guess if I wake up and do low intensity "morning cardio" for say, 45 min, I will be sparring the most muscle while burning the most fat?

 

[drbenroth]

its not percentage of energy from fat that we are worried about, it is total amount of fat.
overnight, you are burning a very high percentage of fat. a very high percentage of a very low number.
more intense cardio, although burning a lower percentage of fat, still generally burns a much greater total number of calories from fat, and also keeps the metabolism raised for much longe, as well as not being completely boring.

fat burning zones are for fat women who want to stay fat.

 

[studen77]

fat burning zones are for fat women who want to stay fat.

Ok, but look has anyone tried this approach? I'm always worried about muscle loss in my 45min-1hr HIIT cardio sessions..and this research they did (I think) addresses some of my worries...I just wanna know if anyone has done low intensity cardio for AT LEAST 45min and the results they achieved..

I may try this for a week and see what happens

 

[CowPimp]

In my opinion, you always want to push it as hard as you can for the set duration you plan on doing cardio. You burn more calories this way and promote a greater EPOC (Excess post-exercise oxygen consumption), which means an elevated metabolism for hours after the session ends.

Think about it like this. Example:

The number of calories you burn in a day is 2000. You will perform a cardio session at low to moderate intensity lasting 45 minutes and burning 300 calories first thing in the morning. Total for the day, you will burn 2300 calories. That day, you are going to eat 2300 calories. So, first thing in the AM you burn those 300 calories of almost pure fat. Awesome! Well, guess what? Since you only burn 2000 calories the rest of the day and consume 2300 calories, you have created a positive energy balance for the remainder of the day. Those 300 calories will get stored as fat again. You are back where you started.

Take the same scenario, but this time you will perform a 20 minute cardio session at high intensity in the middle of the day which will also burn 300 calories. You consume your 2300 calories, and you use 2000 calories + the cardio session's 300. Guess what? No difference.

Calories in vs. calories out. Good game, thanks for playing.

 

[drbenroth]

i think the answer to your question is no.
not that it wont work.
but probably nobody has tried it

 

[wilwn]

its not percentage of energy from fat that we are worried about, it is total amount of fat.
overnight, you are burning a very high percentage of fat. a very high percentage of a very low number.
more intense cardio, although burning a lower percentage of fat, still generally burns a much greater total number of calories from fat, and also keeps the metabolism raised for much longe, as well as not being completely boring.

exactly.