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Total Depletion and Replenishment of Glycogen Stores

Total Depletion and Replenishment of Glycogen Stores

This is the very first step bodybuilders commonly use during the pre-contest period. Glycogen is the glucose polymer stored either in the skeletal muscles or liver. It serves as fuel for energy, but its release from the skeletal muscles occurs under different stimulus compared to its release from the liver depots.

Liver glycogenolysis (the glycogen breakdown process) occurs in order to maintain an adequate blood level of glucose to satisfy brain requirements; instead muscle glycogenolysis occurs only during emotional and/or physical efforts in order to satisfy the need for energy.

Glucose is a molecule that consists of Carbon, Hydrogen and Oxygen... in fact its chemical structure is: C6 H12 O6. It contains water!

Let's see why that is so important!

In normal conditions the skeletal muscle glycogen concentration ranges from 1.5 grams to 2 grams per 100 grams of skeletal muscle tissue. A Swedish researcher BERGSTROM (1969) has shown that after a low carbohydrate diet that lasts for a period of 3 days accompanied with prolonged physical exercises/efforts one's skeletal muscle glycogen depots fall to a concentration of about 0.6 grams! After this limited 3 day period of carbohydrate depletion, a carbohydrate-rich diet was followed causing a new higher level of muscle glycogen content.

As you may see from figure number 1 above, marathon contestants also use the method of downloading and reloading the glycogen through diet manipulation before the marathon. As shown in the figure, exercise is gradually reduced during the week and the carbohydrate intake of the diet is increased for the last three days. (From Sherman, W.M., et al.: Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. Int. J. Sports Med., 2:114, 1981).

The consequences of this study have been of great utility for those endurance athletes whose performance is high and who need larger amounts of ready-to-use energy stored as glycogen. Furthermore, these results apply very well to bodybuilders too. You may be wondering why an increase in glycogen depots should be an aid for a bodybuilder during the show.

Here's the reason:

If the "depleting glycogen phase" has been done correctly, inducing a dramatic lowering of glycogen depots, it creates a "hunger state" for your muscles so that during the next "super compensation" phase they will store more glycogen than in normal conditions. In other words, they could store from 3.5 grams of glycogen to even 4 grams per 100 grams of skeletal muscle tissue. Don't forget that 1 gram of glycogen is linked with 2.7 grams of water. This means that if a bodybuilder has 45 kg (99 pounds) of Lean Muscular Tissue, (don't confuse Lean Muscular Tissue with Fat Free Mass; Lean muscular tissue is in other words "MUSCLE", instead Fat Free Mass consists of Lean Muscular Tissue + Bones + Water) he can increase his bodyweight about 4.86 kg (10.69 pounds) with glycogen and water during the carbohydrate loading phase.

The calculation goes like this:

1) Kg 45 x 10 = 450 hg

(Kg of skeletal muscle converted into hg; 1 kg equal 1000grams, 1 hg equal 100grams)

2) hg 450 x 4 = 1800 grams (total muscular glycogen content)

(the number 4 stands for the maximum glycogen content per 100 grams of muscle tissue)

3) 1800 grams x 2.7 = 4860 grams (final bodyweight achieved)

(2.7 is the grams of water linked to 1 gram of glycogen)

All this weight gained comes from glycogen and water. It's not water retention! Water retention means that water is being kept between the cells (in this case between the muscle cells) giving the muscles that smooth look that won't give you that ripped look that is so hard to reach after all the sacrifices that you made while preparing for competition. The water gained is all carried into the muscle cells because glycogen depots are located only inside and not outside the muscle and liver cells. That's why this loading phase makes the muscles appear bigger and fuller!

To cause this "supercompensation" it is very important to reload the right amount of carbs. The consumption of fewer carbohydrates than those needed won't lead to the desired effect and you may even notice that your muscles feel empty and become smaller. This is what usually happens to competitive bodybuilders! If this does happen, it would have been better NOT to have done the "depleting carb phase" at all.

If the consumption of carbs exceeds the amount needed to refill all your glycogen depots completely, that surplus will be converted into subcutaneous bodyfat. NOT GOOD.

Now you probably want to know how many carbs you should be eating in order to refill all your glycogen depots while avoiding the risk of reducing your muscle size or gaining bodyfat.

The recommended carbs consumption has been estimated at 400 to 600 grams per day for a period of 3 days after the depleting phase. There are also other very reliable experts on bodybuilding that instead of suggesting the 3 day depleting formula, they opt for 2 days for depleting and 2 days for reloading. My opinion on this is that the difference between the number of days for depleting and reloading is strictly personal and not applicable to everybody; and this is for many different reasons. Even the good results obtained with different schedules on different individuals cannot be simply applied directly to everyone else.

The factors that contribute to the different responses that people get are mainly due to either genetics and/or their personal training schedule during the depleting phase.

(A) Genetic factors

  • Personal ratio of FTF (Fast Twitch Fibers) to STF (Slow Twitch Fibers)

Personal Ratio Of FTF To STF

During evolution, the human being developed its muscular structure as well as its muscular functions to adapt himself to the environment. In fact, the muscular skeletal ratio of FTF to STF has been set to satisfy that same purpose: SURVIVING!

Since the STF muscle fibers are characterized by a "resistance" quality and low fatigability, they developed on the body within those areas that are involved in continuous movements (such as walking, long running etc.) and efforts that require (of course) resistance: lower limb, abdominal wall, and so on!

The upper limbs instead are mostly composed of FTF to match different purposes from the other fibers, like rapid movements (such as throwing, fighting), and strength etc., but not resistance. Even though this is the general distribution, each of us has a different ratio of these fibers in our bodies. This is an important factor because the capacity to use glycogen varies enormously in these two types of fibers.

FTF are the glycolitic fibers, meaning that they use primarily glycogen for energy production. STF are the oxidative fibers, meaning that they need oxygen to produce energy and they need oxygen to completely oxidise the organic substrates.

FTF generate energy even when oxygen is not available to them, during pure anaerobic efforts like when weight training with a max rep range of 12 (while using a weight that is heavy enough to only allow you to get 12 reps).

STF are mostly recruited during aerobic efforts, like running, jogging, etc., but also during weight training where the number of reps goes beyond 12.

Returning to our purpose, we aim to deplete our glycogen stores as much as possible and this depends on your genetic predisposition to the fiber ratio as well as the kind of workout you follow. If you do have a favourable ratio of FTF to STF in your muscles, you would hold more glycogen depots than if you had the contrary, and this in turn translates to more glycogen that can be stored during the replenishment phase.

Training Schedule During The Carbohydrate Depletion Phase

The training schedule that should be followed during the carb depletion phase has to aim to cause drastic skeletal muscle glycogen depletion.

(B) Type Of Training

During the 3 days of "Carb Depletion", weight training should be performed on every one of these 3 days. All the muscle group should be trained. Usually a whole body circuit is followed, consisting of one set per muscle group. After the whole body has been hit, a new circuit starts and so on, until exhaustion won't allow you to go on. Usually the circuit is followed 3 to 4 times in a row.


Chest 1 x 8-12
Latissimus dorsi 1 x 8-12
Deltoids 1 x 8-12
Biceps 1 x 8-12
Triceps 1 x 8-12
Abdominals 1 x 12

To be repeated another 2 to 3 times.

As you may notice there's no exercise for the legs! This is because the quadriceps need at least 7 days to get deep cuts and look defined after the last workout.

Other experts work each muscle group with 3 to 4 sets in a row instead of doing one set and moving on to the next exercise. Even though this practice will allow you to feel much more of a pump, it could exhaust you before you hit all your muscle groups.

Number of Reps per Set

The muscle fibers that need to be stimulated are of course the FTF, the Glycolytic ones, since these are the only fibers that show a high affinity for anaerobic glucose catabolism (anaerobic glycolysis) and are then able to breakdown glycogen into glucose for energy production during high intensity lactacid anaerobic training.

This has been shown because the enzyme Phosphofructo kinase (PFK) is highly active when these kinds of fibers are stimulated. This enzyme plays a dominant role in regulating the glycolytic process. In fact this enzyme operates in the isomerization catalysis process of Glucose-6-phosphate into Fructose-6-fosphate.

This is a process that occurs in the cytosol only when glucose has to be used for energy production. This shows that the stimulation of FTF is highly connected to the catabolism of glucose. Most of this glucose derives directly from muscle glycogen breakdown therefore ultimately causing its depletion.

The STF instead have oxidative metabolic properties and very poor glycolytic ones. This has been shown by the observation of the activity of the enzyme "Succinic Dehydrogenase" (SDH) that plays a crucial role in the oxidative metabolism.

This enzyme permits both the conversion of the Succinic Acid into the Fumaric Acid (this happens in the Krebs Cycle inside the mitochondria) that is important for continuing the Krebs Cycle and the Reduction of the Co-Enzyme FADH2 which in turn is involved in the production of ATP inside the "Transport Chain of Electrons" on the inner membrane of the mitochondria. Even though this chemical reaction is very important in the energy production process, it has no impact on glycogen stores as much as PFK does when FTF are properly stimulated.

All this is to clarify that the stimulation of STF is useless for promoting the muscle glycogen depletion in the best way possible.

Remember that your goal is to create that "hunger muscle state" that will allow you to increase the glycogen depots as much as 4 grams per 100 grams of muscle tissue during the "Carb Replenishment Phase". To cause this, the best kind of training should consist of a "Lactacid hypertrophic" workout with reps in the 8 to 12 range per set. This range of reps stimulates the FTF at their maximum, in fact the High Lactic Acid production that this causes is the natural proof of their stimulation, because lactate is the last step of anaerobic glycolysis when Pyruvate goes under reduction because of the absence of Oxygen availability.

In this case lactic acid is derived from glucose catabolism (glycolysis), and glucose is derived (in this case during weight training) from glycogen catabolism (glycogenolysis).

A lower number of reps (with a heavier weight) involves the FTF much more than a moderate weight lifted for 12 reps but the energy substrates to which the FTF rely on to produce energy is not glucose deriving from glycogenolysis, but ATP CP. A range of reps that goes beyond 12 begins to stimulate more STF than FTF.

To sum this all up, stay in a range of 8 to 12 reps during the depleting carb phase in order to assure glycogenolysis as much as possible for energy production.

Time Of Recovery Between Sets

During the first reps of the first set, the muscle burning effect is absent because the Lactate has not yet been produced. In fact, in the very first reps the molecule used to produce energy is ATP that is stored in the muscles. The degradation for energy purposes of only molecules of ATP and CP (Creatine Phosphate) that are stored into the muscles is called "Anaerobic Non-Lactacid Metabolism" because it doesn't produce any lactate.

It is important that you know this to understand the right time for recovery between sets.

Once the set is over ATP depots get replenished through different mechanisms and it takes about 3 to 5 minutes. If the set is restarted before the ATP molecules have been re-synthesised and are ready to be used, the ATP for energy production needed for the next set will come from glycolysis that in turn comes from glycogenolysis.

The less you rest between sets the more glycogen you use for energy production and the more glycogen you use the higher its depletion in your body. Try not to exceed 1 to 1 1/2 minutes between sets.


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