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

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?

Originally Posted by 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.

exactly.