ATP vs. Glycogen

[health0507]

Would like more clarification between the two--in simple terms (aka dumbed down version please). Do I understand correctly that both store/supply your muscles with energy? I know there is a difference though. Please don't repeat wikipedia, because that's why I came here in the first place. Peace!

[RealMenDeadLift]

Glycogen is used as substrate for ATP synthesis during intense exercise.

You have a very small storage of ATP in your muscle cells. Within the first few seconds of exercise that is quickly used up, followed by your stores of phosphocreatine for another few seconds, and then you begin using glycogen.

During your rest periods those short-burst energy stores(ATP and PCr) are replenished for your next set.

[health0507]

RMD, thanks for the quick reply. If say during my first set, I get to glycogen stores and then rest, will my next set go back to using ATP, PCr before going back to glycogen? ATP/PCr must replenish pretty fast if it happens between sets.

[Opies]

RMD, thanks for the quick reply. If say during my first set, I get to glycogen stores and then rest, will my next set go back to using ATP, PCr before going back to glycogen? ATP/PCr must replenish pretty fast if it happens between sets.

Everything moves fast on the cellular level.

[in10city]

RMD, thanks for the quick reply. If say during my first set, I get to glycogen stores and then rest, will my next set go back to using ATP, PCr before going back to glycogen? ATP/PCr must replenish pretty fast if it happens between sets.

For the vast majority of the duration of a bout of anaerobic exercise lasting over a few seconds, ATP is not being provided by one exclusive source. The ATP is supplied by ATP/PCr hydrolysis, and anaerobic and aerobic ATP production from carbohydrates [glycolysis and oxidative phosphorylation]. In fact, glycogenolysis in muscle speeds up within seconds of the onset of muscle contraction and begins to pick up the slack to maintain energy production as PCr's output falls. Furthermore, the energy source distribution changes as successive bouts of exercise are performed.

[health0507]

in10, not quite the dumbed down version (for me at least) but I think I get it. So how exactly does "the energy source distribution change as successive bouts of exercise are performed"? Now, I'm just curious. Thanks.

[RealMenDeadLift]

in10, not quite the dumbed down version (for me at least) but I think I get it. So how exactly does "the energy source distribution change as successive bouts of exercise are performed"? Now, I'm just curious. Thanks.

There is a shift towards glycogen being the primary source of ATP production as your initial ATP stores and PCr stores are used up after several sets.

At first, the first few seconds of ATP production comes primarily from existing ATP and PCr stores, but as those become used up after several sets, Glycogen becomes the primary source of ATP.

[in10city]

in10, not quite the dumbed down version (for me at least) but I think I get it. So how exactly does "the energy source distribution change as successive bouts of exercise are performed"? Now, I'm just curious. Thanks.

Here is an example of the 1st and 3rd bouts of 30 sec maximal execise with 4 minutes rest between to allow for near full PCr resynthesis so it could contribute ATP again.


http://ajpendo.physiology.org/cgi/co...ull/277/5/E890

The ATP concentration in muscle is strongly defended and even after the most intense bout of exercise, it may decrease 20-50% which means that metabolic pathways that provide ATP nearly match the rate of ATP consumption during exercise. If ATP were to be totally used up, you would experience rigor mortis since the ATP-dependant detachment of myosin heads from actin wouldn't occur. Since PCr is resynthesized rapidly, in 60-90 seconds, it is the first line of defense assuming intermittent exercise bouts are being performed. However its provision wanes over time and in the case of shorter rest periods and incomplete PCr resynthesis its provision and duration of contribution would also tail off. So other metabolic pathways of ATP have to pick up the slack [glycogen being the primary substrate and extracellular glucose can contribute a small amount depending upon the conditions at hand]. The aerobic/oxidative phosphorylation ATP provision becomes increasingly important during repeated bouts.

[RealMenDeadLift]

If ATP were to be totally used up, you would experience rigor mortis since the ATP-dependant detachment of myosin heads from actin wouldn't occur.

That would be fun to see happen

[health0507]

in10, thanks for the graph. Do I presume correctly that glycolysis and oxidative phosphorylation is the process in which glycogen is used?

[RealMenDeadLift]

in10, thanks for the graph. Do I presume correctly that glycolysis and oxidative phosphorylation is the process in which glycogen is used?

Glucose is metabolized via glycolysis with the chief product being pyruvate. That pyruvate then fuels the TCA Cycle which supplies the necessary coenzymes for oxidative phosphorylation.

[in10city]

in10, thanks for the graph. Do I presume correctly that glycolysis and oxidative phosphorylation is the process in which glycogen is used?

Almost. Being more specific with how the two relate to each other... glycolysis is the formation of pyruvate + ATP by substrate-level phosphorylation [and some other stuff] from a common starting point of glucose-6-phosphate which comes from the breakdown of glycogen [glycogenolysis] or the phosphorylation of glucose. Depending upon the biochemical and redox state, some pyruvate can be reduced to lactate and that's a terminal pathway [actually the lactate can be taken up by consuming tissue, converted to pyruvate and then Acetyl CoA for catabolism in the tricarboxylic acid cycle or converted to glucose by the liver so it's really not a dead end metabolite]. The other primary pathway for pyruvate to continue on would be the conversion to Acetyl CoA and catabolism in the tricarboxylic acid cycle to produce ATP or GTP by substrate-level phosphorylation and the reducing equivalents NADH and FADH2 - which are then transferred to the electron transport chain to generate more ATP by oxidative phosphorylation - the process by which the free energy created from the flow of electons through the electron transport chain is used to form ATP.

Or more simply:
a) Glycogen/glucose -> glucose-6-phosphate -> glycolysis -> pyruvate -> lactate
b) Glycogen/glucose -> glucose-6-phosphate -> glycolysis -> pyruvate -> Acetyl CoA -> tricarboxylic acid cycle -> reducing equivalents -> oxidative phosphorylation

Keep in mind that glycolysis isn't exclusive to glycogen since glucose can be catabolized too, nor is the tricarboxylic acid and oxidative phosphorylation exclusive to just carbohydrate metabolism.

[health0507]

Thanks in10 and RMD! Sure I don't understand all the details, but I now have a general concept of it all. Peace!