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Suppose I do the following exercise:

As many body weight squats as possible in 1 minute without stopping with a 10 second rest. Repeat 15 times.

Would this deplete the muscle glycogen in my legs? What impact would this have on overall fat burning?

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    Your question is very broad without a stated purpose. – rrirower Dec 21 '14 at 2:44
  • Not only broad, but it is a speculative "What if" question which is off topic on every SE site. – JohnP Dec 21 '14 at 13:46
  • It's not a "what if", it's "How much? This much?" I agree that it's broad enough to be two questions -- one is about what it takes to deplete muscle glycogen, one is about what depleting glycogen does for fat loss. The first question's interesting and has a factual answer, the second I would edit out. – Noumenon Jan 3 '15 at 2:08
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Here's a study (http://link.springer.com/article/10.1007/BF00422734) on intense and prolonged, heavy-resistance exercise of leg muscles (so with weights, not just body weight), and after repeating intense sets of different leg muscle exercises - the glycogen levels in the muscles weren't even halved - so while this study doesn't directly prove it - I don't think it's impossible to deplete your glycogen reserves in any muscle group under the conditions you described.

And as far as the effect of this kind of exercise on overall fat burn goes, I have found two studies that can provide some insight...

According to this study (http://ajpendo.physiology.org/content/292/2/E394) exercising a particular muscle can increase the breakdown of fats in that particular area, but the increase of the breakdown rate is relatively small and it only happens during exercise, which is confirmed by...

...the second study (annals.org/article.aspx?articleid=685223), that suggests that even if you train a particular muscle group more than other groups, the sub-skin body fat will remain unchanged - confirming that in the long run, your body has a way of evening things out...so you can probably rule out any extra body fat burns on account of this.

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Back of the envelope calculation:

I assume your weight is 75kg, you workout intensely for 16 min and 30 secs, this would amount to about 190 kcal (compared to running which is about 10*BW kcal/hour)

"A well-nourished adult can store approximately 500 grams or 2000 kcal of carbohydrates. Of this, approximately 400 grams are stored as muscle glycogen, 90-110 grams as liver glycogen, and 25 grams circulate in the blood as glucose." [1]

Each leg is about 10% of your body weight [2], this should mean that about 2*0.1*400*4 kcal = 320 kcal are stored in the legs. This is probably a relatively low number considering the fact that legs are dense in terms of muscle, compared to the torso which is filled with organs and other non-muscle tissue.

So my conclusion is that you will deplete your leg muscles to about 50%, but you don't have to completely deplete your muscle glycogen to have lipolysis (fat release) due to the exercise. There is no definite connection between temporary lipolysis and total fat level changes though. So the "total effect on fat burning" will as always, completely depend on your diet, if you eat enough, fat storage will be higher than fat burning, and you will have a net gain.

[1] http://www.extension.iastate.edu/humansciences/content/carbohydrate

[2] http://www.askabiologist.org.uk/answers/viewtopic.php?id=1477

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