PWO : Split - Muscle Glycogen and Liver Glycogen

[kp1512]

Ok, so I was thinking about the breakdown of glycogen replishment, and it being done (or required) via two mechanisms.....Simple carbs (non-fructose) and thus for Muslce Glycogen, and then Liver Glycogen.

Now, assuming you are working out on pretty much in a okay state (glycogen) is there a need to replenish Liver Glycogen? I am assuming not?..As its actual muscle glycogen thats been used up?...Similar to how when we sleep, one of the first things that may need addressing in the morning is a slight dip in liver glycogen?.......

If some of the above is true, then drinking fruit juices PWO and consuming fruit generally as part of PWO is pretty much useless as the carbs cant be used for muscle glycogen replenishment.......? and the only time there really needed are in the morning (if you wanted to choose a more efficient energy source)

KP

[mxd]

I take around 10g glutamine in the morning and around 30 g around workout
I've all ways thought that sufficient to cover liver glycogen.?

[Dtlv74]

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Ok, so I was thinking about the breakdown of glycogen replishment, and it being done (or required) via two mechanisms.....Simple carbs (non-fructose) and thus for Muslce Glycogen, and then Liver Glycogen.

Now, assuming you are working out on pretty much in a okay state (glycogen) is there a need to replenish Liver Glycogen? I am assuming not?..As its actual muscle glycogen thats been used up?...Similar to how when we sleep, one of the first things that may need addressing in the morning is a slight dip in liver glycogen?.......

If some of the above is true, then drinking fruit juices PWO and consuming fruit generally as part of PWO is pretty much useless as the carbs cant be used for muscle glycogen replenishment.......? and the only time there really needed are in the morning (if you wanted to choose a more efficient energy source)

KP

This is an assumption I've been working on for a while. Most days I normally eat one or two pieces of (different) fructose containing fruit immediately upon waking for the purpose of replacing liver glycogen. A spoonful of honey is also a good choice. I then lay in for 15, get up, dressed etc, and then start my main breakfast feed.

[NU_nutrition_TS]

Yes, serum glucose is kept stable overnight [or during fasting] by the liver reconverting some of its glycogen into glucose and releasing it into the bloodstream. So any carbohydrate consumed first thing will likely be converted into liver glycogen to top up its stores. It may be that a degree of gluconeogenesis also contributes to the overnight blood glucose balance and, maybe, replacement of liver glycogen - though this is an intuitive thought on my part and I have not researched that specific point!

During physical activity it is obviously muscle glycogen [among other substrates] that is used to fuel muscles but, as I have previously posted elsewhere, it is thought that muscle glycogen acts as a buffer for serum glucose to flow into and out off while indirectly fuelling the muscle cells. So, as serum glucose falls, the liver will breakdown some of its glycogen to keep the serum glucose level topped up. In which case any refeeding after a workout may be diverted to the liver before the muscles - or simultaneously replenish both!

[kp1512]

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During physical activity it is obviously muscle glycogen [among other substrates] that is used to fuel muscles but, as I have previously posted elsewhere, it is thought that muscle glycogen acts as a buffer for serum glucose to flow into and out off while indirectly fuelling the muscle cells. So, as serum glucose falls, the liver will breakdown some of its glycogen to keep the serum glucose level topped up. In which case any refeeding after a workout may be diverted to the liver before the muscles - or simultaneously replenish both!

So is there anything to suggest it is chronological?....I havent found anything to suggest that, but the reason why this question came about is that, in my opinion, a very well respected US based supplement company is trialing out this new Pre and Pwo mix, and its using handful of BBs and its mix comprises of various including crystalline fructose at no more then 8-10g per drink mix...and it appears that those taking this supplement seem to be reporting faster fullness in muscle...and to them, recovery.....so it just made me think........MAYBE liver glycogen IS important?.....PWO?...Or PWO?

KP

[cleaver]

taken from

Quote

Regulation of Blood Glucose Homeostasis during Prolonged Exercise
Sang-Hoon Suh*, Il-Young Paik, and Kevin A. Jacobs

Laboratory of Sports Physiology and Medicine, Department of Physical Education, Yonsei University, Seoul 120-749, Korea;
Department of Exercise and Sport Sciences, University of Miami, 5202 University Drive, FL 33146, USA.

Yes it does refer to prolonged exercise but here are some interesting points which must apply to all exercise

Quote

Regulation of hepatic glucose production during exercise

Maintaining adequate blood glucose supply is critical during exercise because it constitutes an appreciable fraction of the fuel for the working muscle and, as is the case at rest, supplies virtually all the fuel for the central nervous system.

During the early stages of exercise, muscle glycogen is the chief source of energy for contraction, whereas circulating glucose and non-esterified fatty acids become essential with increasing exercise duration.

An increase in exercise intensity amplifies the need for carbohydrates,and intra- and extra-muscular sources of glucose are utilized at greater rates (Brooks and Mercier,1994). Despite the reliance of the working muscle on glucose,arterial levels are generally constant.

The liver plays an important regulatory role in maintaining blood glucose homeostasis by matching the increased rate of muscular glucose utilization with a quantitatively equal rate of glucose production.

Thus, to maintain glucose homeostasis and sustain glucose delivery to muscle under these conditions, the liver must conserve carbon-based compounds, such as lactate, glycerol, and certain amino acids by channeling them into the gluconeogenic pathway.

During moderate intensity exercise, the blood glucose level remains relatively constant, despite a marked exercise-induced rise in peripheral uptake of glucose in contracting muscle uptake (Kjaer et al., 1991), and a major drop in blood glucose is not observed unless exercise is prolonged for several hours (Ahlborg et al., 1974). Thisindicates that the exercise-induced rise in hepatic glucose output matches the increased glucose uptake by contracting skeletal muscle as long as sufficient stores of glycogen are present in the liver.

In contrast, if exercise becomes more intense, blood glucose is usually found to increase in humans, indicating that the hepatic glucose output exceeds the peripheral glucose uptake (Kjaer et al.,1991).

This confirms the hypothesis that mechanisms other than feedback regulation to maintain euglycemia are involved in the mobilization of glucose from the liver
during exercise.

[NU_nutrition_TS]

I think liver glycogen probably is important during training [for the reasons already given] and another reason is that the body seems to preferentially work in this way: a series of storage media all feeding into each other. As another example, take the bile duct. Bile is synthesized in the liver but stored in the bile duct. There it becomes more concentrated. When a fatty meal is ingested the concentrated bile released from the bile duct into the gut to help emulsify the fats in the meal. More bile is synthesized in the liver and stored in the bile duct ready for the next fatty meal. Similarly with the appendix, now thought to be a storage depot for the beneficial bacteria that populate the gut and form part of the immune system. When the good gut flora get wiped out due to infection and/or treatment with antibiotics, the flora living in the appendix are able to repopulate the gut and restore immune function. it is not such a great leap to imagine that liver glycogen, muscle glycogen and adipose tissue serve the same 'storage' function for glucose. As glucose can only be tolerated in the blood stream in very small amounts at any one time point, it seems logical that the body would develop multiple interlinked storage sites and mechanisms to keep blood glucose maintained at very tightly controlled levels at all times and still have sufficient in reserve for extreme energetic demands - like physical exercise.

As you begin to exercise intramuscular fatty acids, then increasingly, muscle glycogen derived glucose fuel the muscle cells, as muscle glycogen is broken down serum glucose is drawn into the cells to begin reconstituting the glycogen [hence serum glucose flows into and out of glycogen]. As the serum glucose levels fall the liver converts some of it glycogen back into glucose to top up serum levels so that everything remains in balance. If the exercise continues for a lengthy period like a workout or sporting event [something the body hasn't really evolved to to do on a regular basis] then a degree of gluconeogenesis probably kicks in to take the glycerol left over from the fat used as an energy substrate, the lactic acid produced as a by product of glucose use as an energy substrate and carbon skeletons left over from amino acid deamination to make endogenous glucose to help balance serum levels. When the activity is finally over and the body is at rest these mechanisms will continue to tick over [esp. gluconeogenesis] along with PWO refeeding to replenish liver and muscle glycogen. Since we rely on liver glycogen to keep serum levels stable [for the brain to operate mainly] it makes sense that it would take priority [so, chronologically, would be topped up first].

Maybe that is the logic of including a small amount of fructose in the formula you mention, as it tends to preferentially [I think I read!] top up liver glycogen, thus leaving the other carbs in the formula to go directly to muscles?

Ha! Cleaver got there first...well done, matey!

[kp1512]

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taken from



Yes it does refer to prolonged exercise but here are some interesting points which must apply to all exercise

Thats very interesting...and may possibly address why this supplement may be working..?.....So, from that, did you; like me, read that the more intense the exercise the more potent the chance of liver glycogen being called upon?

KP

[kp1512]

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As you begin to exercise intramuscular fatty acids, then increasingly, muscle glycogen derived glucose fuel the muscle cells, as muscle glycogen is broken down serum glucose is drawn into the cells to begin reconstituting the glycogen [hence serum glucose flows into and out of glycogen]. As the serum glucose levels fall the liver converts some of it glycogen back into glucose to top up serum levels so that everything remains in balance. If the exercise continues for a lengthy period like a workout or sporting event [something the body hasn't really evolved to to do on a regular basis] then a degree of gluconeogenesis probably kicks in to take the glycerol left over from the fat used as an energy substrate, the lactic acid produced as a by product of glucose use as an energy substrate and carbon skeletons left over from amino acid deamination to make endogenous glucose to help balance serum levels. When the activity is finally over and the body is at rest these mechanisms will continue to tick over [esp. gluconeogenesis] along with PWO refeeding to replenish liver and muscle glycogen. Since we rely on liver glycogen to keep serum levels stable [for the brain to operate mainly] it makes sense that it would take priority [so, chronologically, would be topped up first].

Maybe that is the logic of including a small amount of fructose in the formula you mention, as it tends to preferentially [I think I read!] top up liver glycogen, thus leaving the other carbs in the formula to go directly to muscles?

Ha! Cleaver got there first...well done, matey!

There definately seems to be something to this I think....but I just didnt beleive adding crystalline fructose or, even maybe a few apples at worse, would make that much of a difference.....but its seeming to.....for the efforts of 5-10g seems unbeleivable...but in reality its providing good feedback.....

KP

[cleaver]

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Thats very interesting...and may possibly address why this supplement may be working..?.....So, from that, did you; like me, read that the more intense the exercise the more potent the chance of liver glycogen being called upon?

KP

Yes

But it also says that the liver conserves various aminos ready for gluconeogenis. I have a funny feeling that by the time you consumed frutose your liver will have done the biz and converted aminos to replenish any lost glycogen.