Teach me about glycogen

I tried to scan the wiki for a general overview, but it's way sciencey. Pretty sure I'd be the one asking you to explain it.

Glycogen is a starch produced mostly in the liver and muscles by chaining molecules of glucose together. When blood sugar rises, the pancreas secretes insulin, and insulin stimulates the movement of blood-sugar (glucose) into the liver, muscles, and other cells, to be used as glucose or stored as glycogen. When blood sugar drops, glucagon is released by the pancreas, and glucagon stimulates the break-down of glycogen and the production of glucose. This glucose is released back into the blood stream to be used as energy.

In terms of exercise... I can only talk about basic human physiology. I just don't know all the ins and outs of human nutrition and exercise science, so... I could be preaching something that's not quite accurate. But anyway

When you exercise, you burn up the glucose that's in your blood stream, triggering the break-down of glycogen and release of glucose from the liver and muscles, which raises your blood glucose and helps you continue on with your exercise. Eventually, you can deplete your glycogen stores. Marathon runners talk about 'hitting the wall' and from what I've read, that wall is the depletion of glycogen and is rather painful (not pain "ouch", but pain as in muscles burn and you're really tired) because your body has to scramble for an alternative energy source to keep you on your feet.

So glycogen is good, especially if you are doing something that requires endurance.

But there's another side to all this- and that's the insulin/glucagon side of things. And this is where things get a little murky for me, because the science isn't cut-and-dry. Prevailing theories change and I'm just not sure what's 'new' and most accurate. What I do know is this: Insulin stimulates the conversion of glucose to glycogen, but it also stimulates the synthesis of fat, which is stored in adipose tissues. You hear a lot about low glycemic diets, and the logic there is that you want a slow release of glucose from the gut into the blood-stream. The slow release avoids spikes in blood glucose levels, which keeps insulin levels from spiking, which promotes glycogen storage but not fat storage.

The other thing I know is that exercise makes your body more sensitive to insulin and glucose levels. You become more efficient at using them, better at storing that glycogen. This is one of the reasons exercise is soooooo important for the type II diabetic. Type II diabetics are insulin resistant... their bodies can't move glucose from the blood to their cells, so blood sugar levels rise. But muscle contraction causes sugar-absorbing proteins to move to the surface of the cell with or without insulin, and those proteins move the sugar from your blood into your cells so that you can actually use it.

And that's about all I know about that

Oh... except brain glucose.

If you really want to learn about sports nutrition, I have a great site for you:

http://btc.montana.edu/olympics/default.htm

http://www.youtube.com/watch?v=h0Qqer8rFkA

Glycogen is stored energy. When you work out it's used as fuel for your workout. Carbs are important to restore glycogen.

Hey there-- what is it that you were wanting to know about glycogen, anything specific? In general, glycogen is stored in several places and is basically how your body stores sugar to use as energy. You have muscle glycogen, glycogen in the liver, etc. When exercising... let's say you're doing strength training and you're doing a set of... 25 chest presses at a light weight (near failure @ 22-24), which is a good rep range for muscle endurance / fat loss, then your body burns energy in this way:

First 5-10 seconds, your body uses ATP for energy
Approx 10-15 seconds, your body uses ADP + Creatine for energy,
After that, glycogen is used, then after glycogen is depleted, fat stores are used for energy

Numbers may be slightly off, but in general that's how it works. Your body stores about 300-400 calories worth of glycogen in your liver, something to keep in mind when thinking about duration of cardio / exercise.

Hope that helps! I'm a trainer so I reference this stuff almost daily

Whatever glucose(sugars and carbs) you have consumed that your body doesn't need gets converted into glycogen and stored in the liver for later use, but if there is too much it can get stored as fat. It is a form of energy. Your body needs sugars and carbs to run.