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Precise mechanism of fat burning?



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MPLANE37
SparkPoints: (64,464)
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Posts: 2,166
12/16/11 4:09 A

Thank you, SP_COACH_DEAN. I got it.



SP_COACH_DEAN
SparkPoints: (90,394)
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12/15/11 10:30 A

Hi, M

The issue of muscle loss isn't really about the use of muscle protein to fuel exercise. Your body can't break down muscle tissue and turn it into ATP fast enough to use it as a significant fuel source for aerobic exercise. Your body is constantly in the process of breaking down "old" muscle protein and synthesizing "new" protein to replace it and/or build additional muscle as needed. You will lose muscle mass when protein breakdown exceeds protein synthesis, and gain muscle mass when the opposite is true.

Both of these states happen at multiple times during a typical day, and whether you end up gaining or losing muscle mass is influenced by two main factors. For practical purposes you'll lose muscle mass when your calorie intake is less than you need for energy balance and you aren't stimulating your body to replace the muscle protein that is naturally being broken down all the time. When that happens, some of the protein stored in your muscles will be used to provide fuel for whever your body needs it for at the time, but that isn't typically caused directly by exercise itself (unless you're talking about really extreme exercise that goes on for hours without adequate hydration and fueling). During weight loss, the lower weight will mean that less muscle is needed to move your lighter body around, and the calorie deficit will mean that you can't add new (additional) muscle mass, so some part of the weight you lose will inevitably be muscle. You can minimize that amount by keeping your calorie deficit reasonable (250-1000, depending on your current weight), and by using exercise and resistance training to give your body a reason to replace lost muscle protein--it's pretty much a "use it or lose it" deal. A large calorie deficit and lack of resistance training has the opposite effect--you lose more muscle as a percentage of total weight lost.

There are other things you can do to minimize muscle loss during weight loss or heavy exercise. Probably the most important are to make sure you have adequate protein in your diet, and to have a "recovery" meal/snack that includes protein within 1-2 hours after an exercise session.

Hope this helps.

Coach Dean

Edited by: SP_COACH_DEAN at: 12/15/2011 (10:41)


MPLANE37
SparkPoints: (64,464)
Fitness Minutes: (34,077)
Posts: 2,166
12/15/11 7:19 A

Thank you both, MOTIVATED@LAST and SP_COACH_DEAN. I know more now. In the article it is mentioned that the preferred fuel for the body is carbohydrates and fat... Still I have no idea how does burning muscle for fuel kicks in... Should you be really energy depleted for a looong time? Or is it that the muscle mass is lost because the muscles have less weight to move around for losing fat, and thus a smaller muscle mass is sufficient for the new lower weight, and the difference is burned just because it is not needed (when, of course, there is no strength training involved)?



SP_COACH_DEAN
SparkPoints: (90,394)
Fitness Minutes: (140,433)
Posts: 15,057
12/14/11 10:18 A

Hi, M

If you want a more detailed explanation of when, why and how your body uses fat and glucose (carbs) to fuel exercise, here's an exercise physiology article that gets into all that. It's a little dense, but not super technical (it leaves out the details of cellular metabolism, at least):

www.unm.edu/~lkravitz/Article%20folder/cal
oricexp.html


Hope this helps.

Coach Dean



SKYWATCHERRS
Posts: 6,315
12/14/11 9:18 A

I just have to say that M@L's response was awesome. emoticon



MOTIVATED@LAST
Posts: 13,914
12/14/11 9:14 A

Fat is not directly usable by muscles as fuel. It needs to be converted into something called ATP by the liver first before it is usable.

But the body can convert fat to energy only slowly. For a less intense workout, the majority of the energy may well come from fat. But for more intense workouts, the body simply cannot convert fat to energy fast enough, and the energy has to come from somewhere else. Carbs are the body's preferred fuel, and carbs are readily usable by the muscles. If there aren't carbs available, the body can also metabolize muscle to make energy available. But this is also a slow process, and in the absence of carbs, the rate at which the body can supply energy to the muscles, and thus the intensity of your workout is limited.

Many people try to work out less intensely, believing that burning fat in their workout will help them lose weight. But this ignores how the body works in reality. After your workout (when energy demands are much lower) the body will convert fat to energy, to rebuild your stores of usable energy. Most of the fat burn comes AFTER your workout, not during. You are better off fueling your body so that you can work out intensely (and thus burn more calories overall), than trying to force your body to burn fat during a workout.

Does that answer your question?

M@L



MPLANE37
SparkPoints: (64,464)
Fitness Minutes: (34,077)
Posts: 2,166
12/14/11 4:28 A

I am curious as to what the precise interplay between carbohydrates and fat in fueling a workout is. How does taking in sufficient amount of carbohydrates increase the fat consumption? Is it by making the exercise more vigorous? Is it by protecting the muscle loss for fueling part of the exercise? Is it by mobilizing the fat stores somehow?



 
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