October 19, 2014

Everything You Need To Know About mTOR, And How To Maximally Stimulate Protein Synthesis

Protein Synthesis Is Activated By mTOR
Activation of protein synthesis is controlled by a series of phosphorylation events orchestrated by a protein called ‘mammalian target of rapamycin’ (mTOR) – which is the master-controller of protein synthesis in the cell, and thus the most important cell signaling complex for muscle growth. Muscle growth is directly related to mTOR activation – greater mTOR activation equals greater protein synthesis, meaning more new proteins are sent out for muscle growth and repair

mTOR Is Activated 3 Ways
·        Mechanical stress (from training)
·        Growth factors (IGF, growth hormone, insulin, etc.)
·        Amino acids (particularly leucine)
Mechanical tension triggers protein synthesis, but the response is limited unless the right nutrition is there to support it, indicating the significance of ‘the anabolic window’ – pre-/intra-/post-workout nutrition.
To provide your body with the opportunity to build maximal muscle, you must exploit the anabolic window because what happens at the cellular level in the hours after training is predictive of long-term gains.

The 3 Most Important Times To Consume Amino Acids
The three most important times for increasing amino acid availability, to facilitate the acute increase in protein synthesis caused by training are:
·        Pre-workout: Within an hour before training.
·        Intra-workout: During training.
·        Post-workout: Within two hours after training.
Nutrition after the workout magnifies the acute, exercise induced increase in protein synthesis the most, but there is still a great deal of value in proper nutrition before, and during the workout.

ATP is burned to fuel muscle contractions during training, which activates and increases levels of a protein called AMP kinase (AMPK), which inhibits mTOR and thus blunts the protein synthetic response. mTOR turns on protein synthesis, AMPK turns it off.
While pre-workout nutrition doesn't improve the post-workout increase in protein synthesis more than exercise alone, amino acid intake before training blunts AMPK mediated inhibition of mTOR, preventing protein synthesis form being turned off during the workout, setting the stage for a more pronounced effect after the workout.

The effect of intra-workout nutrition is similar to that of pre-workout in that protein intake during a workout does increase protein synthesis, but not as much compared to when protein is delivered post-workout, but the main benefit that comes from intra-workout amino acids is the insulin response which powerfully inhibits protein degradation.
Including intra-workout carbs not only inhibit protein degradation, but also blunts AMPK mediated inhibition of mTOR, keeping protein synthesis turned on during the workout, further setting the stage for a pronounced effect after the workout.

Post-workout nutrition is the most important in regards to upping protein synthesis after a workout because that’s when muscle cells are primed for protein synthesis.
The type and timing of protein intake in the post-workout period controls the overall increase in the protein synthetic response that occurs immediately after a workout, and this acute response can determine the long term response to training, which is why training combined with nutrition at precisely the right time is needed to maximally activate protein synthesis.
The amount of potential muscle that can be built is limited if protein intake is delayed for more than two hours after a workout.

The Quality, And Quantity Of Amino’s Needed
The essential amino acids (EAAs) are the only ones that activate protein synthesis, with leucine in particular having the greatest effect, and it's likely that more than 20 grams of protein is needed to maximize this response.

The Role, And Importance Of Including Carbs
Insulin is a potent activator of protein synthesis because it activates mTOR by way of PI3K/akt signaling, a parallel pathway to that used by amino acids and mechanically induced stress activation of mTOR, but the purpose of carbs is not to activate protein synthesis after training since insulin signaling isn't needed to turn on training-induced protein synthesis.
Because insulin signaling isn’t needed to spike protein synthesis in the hours following a workout, the purpose of consuming carbs is because local hyperinsulinemia has a powerful inhibiting effect on protein degradation.

The Duration Of The Protein Synthetic Response
Muscles are primed for increased protein synthesis for over 24 hours after training, but the acute spike in the protein synthetic response to training or amino acid intake, only lasts for a few hours, which is why it’s so crucial to optimize nutrition during this small window. Therefore, each factor contributing the mTOR activation (mechanical tension, amino acid intake, and insulin/growth factors) must be maximized since they all activate mTOR through different, but complimentary pathways, and the more mTOR activating pathways are turned on at the same time, the more synergistic effect there may be.

Combining All 3 Factors To Maximize Protein Synthesis
Because mechanical tension and leucine/EAAs synergistically magnify protein synthesis, and insulin contributes to turning on mTOR through the PI3K/akt pathway, combining insulin with amino acids can synergistically cause the greatest effect on mTOR activation.
Even though insulin doesn't increase exercise-induced protein synthesis, it may act to extend the duration for the protein synthetic response following training, and extending or magnifying the protein synthetic response post-workout is reason enough to consume carbs post-workout, as they can provide a huge muscle building advantage.

Cell Volume Is The Main Driver Of Amino Acid Transport
While getting the right macronutrients at the right times is key, another important yet often unknown/misunderstood aspect of muscle protein synthesis is cell volume, which is the main driver of amino acid transport.

A Volumized Muscle Is An Anabolic Muscle
Cell volume is also linked to protein synthesis, meaning a volumized (full) muscle is an anabolic muscle, as cell swelling inhibits/suppresses protein degradation/breakdown and stimulates protein synthesis (in certain cells – skeletal muscle cells being of greatest importance here).
Protein synthesis is controlled by the enzyme mTOR, which is not only activated by mechanical stress, growth factors, and leucine, but mTOR signaling is also dependent on cell volume. This is especially important in skeletal muscle, where cell volumization activates protein and glycogen synthesis, and inhibits protein breakdown.

Glutamine is considered a ‘conditionally essential’ amino acid, and limits protein breakdown during severe trauma or stress, but is also linked to mTOR activation because glutamine is necessary for cell volumization, and to get leucine into the cell, both of which turn on protein synthesis.
Therefore, cellular glutamine depletion results in both a reduction of cell volume, and reduced ability for leucine to activate protein synthesis.

Cell Volume + Glutamine = Protein Synthesis
There’s a direct link between, cell volumization, glutamine, and protein synthesis because glutamine is what enables leucine to get into the cell to activate mTOR, and turn on protein synthesis, and glutamine induced cell volumization is also turns on mTOR, and thus protein synthesis.
Cell volume (before, during, and after training) is critical for getting amino acids inside the cell, to turn on protein synthesis, and suppress protein breakdown during the workout.

Glutamine Export Is Coupled To Leucine Import, And mTOR Activation
Before leucine can get into the cell, there's an initial period of ‘glutamine loading’, which also pulls in water, increasing cell volume. After the glutamine is loaded, it is exported out of the cell in exchange for the import of leucine.
Cellular glutamine levels are rate limiting for leucine activation of protein synthesis, meaning there is a lag time (roughly 60 minutes) for the activation of protein synthesis by leucine when glutamine is consumed simultaneously with an essential amino acid (EAA) mixture containing leucine, but when cells are ’pre-loaded’ with glutamine, protein synthesis is turned on almost instantly (within 1-2 minutes) after leucine is consumed.

Amino Acid Transport Is Coupled To The Control Of Protein Synthesis
Muscle cells are capable of making glutamine as needed from other amino acids, but protein synthesis in muscle tissue can't remain indefinitely elevated, with or without glutamine supplementation. Glutamine however, can be used to strategically support protein synthesis by optimizing cell volumization during the post-workout period.

The Tertiary Active Transport (TAT) System Is What Gets Leucine Gets Into The Cell
The System ‘A’, and System ‘L’ transport systems are the two classes of amino acid transporters (transport proteins regulate what gets in and out of the cell) that are most closely linked to mTOR signaling and protein synthesis. Their coupled activity is what enables leucine and the other BCAAs to be absorbed into the cell.
System A transporters bring glutamine and sodium into the cell, along with water which causes cell swelling.
System L transporters bring leucine and the other BCAAs into the cell in exchange for the glutamine brought in by System A.
The coupling between sodium uptake and System A / System L amino acid transporters is called Tertiary Active Transport (TAT), and it's TAT which ultimately drives leucine inside the cell leading to mTOR activation and protein synthesis.

First, a membrane bound pump called the sodium-potassium ATPase pump (Na+/K+ ATPase) uses energy from ATP to move sodium outside of the cell (against its concentration gradient).
The increased concentration of sodium outside of the cell is coupled to the import of glutamine by the System A transporter. The influx of glutamine and sodium, along with extra water pulled in, causes the cell to swell, putting the cell in an anabolic state, priming the protein synthetic response.
When glutamine builds to sufficiently high levels inside the cell, the System L transporters are activated which shuttles glutamine outside of the cell in exchange for leucine, and this is what triggers protein synthesis!
Knowing how cell volume is coupled to amino acid transport and protein synthesis enables several nutritional strategies to be designed to maximize the process when it counts most, during the critical post-training period.

The Difference Between The ‘Pump’, And Cell Volume
A ‘pump’ (reactive hyperemia) results in increased volume in the areas in-between, and surrounding muscle cells, also called the ‘interstitial space’, whereas increased muscle cell volume refers to the actual volume of water inside muscle cells (and is what drives muscle growth). While the two are not the same, one (a pump) facilitates the other (increased cell volume).

How The Pump Facilitates Cell Volume
The vasodilation, which occurs in response to training, locally increases blood flow to the working muscles, enhancing the delivery of oxygen and nutrients, as well as removing waste products. This reaction of increased blood flow (reactive hyperemia – the pump), results in increased blood plasma in the areas in-between and surrounding working muscle cells (the interstitial space).
The increased blood plasma combined with the accumulation of lactate and other metabolites increases the osmolarity of the interstitial fluid, which creates a concentration gradient that pulls in additional water from the blood stream, creating a pump.
The osmotic forces that conspire to induce the pump actually encourage cell shrinkage rather than swelling, because if there’s an increase the concentration of solute on one side of a semi-permeable membrane, water will diffuse down its concentration gradient until the system reaches equilibrium. In muscle tissue experiencing a pump, increased osmolarity of the interstitial fluid encourages water to diffuse out of muscle cells and down its concentration gradient, which would actually decrease cell volume.
Thanks to a process known as regulatory volume increase (RVI), muscle cells are able to maintain, or even increase cell volume, in spite of the increase in extracellular osmolarity that occurs during a pump which would logically decrease cell volume.
Because of the coordinated activity of the System A and System L transporter proteins located in the cell membrane, cell volume increases during a muscle pump.
First, the sodium-potassium ATPase pump moves three sodium ions out of the cell, in exchange for two potassium ions. Because the concentration of sodium is typically 10-20 times higher outside the cells compared to inside, energy is required in the form of ATP to pump sodium outside the cell, against its concentration gradient.
Second, another membrane-associated pump called the sodium-potassium-chloride co-transporter pump (NKCC), simultaneously transports one sodium, one potassium, and two chloride ions from outside the cell to inside the cell.
The net result of these pumps (Na+/K+ ATPase and NKCC) results in a net increase of charged ions in the cell, which increases intracellular osmolarity. As intracellular osmolarity increases relative to the interstitial fluid (facilitated by a muscle pump), extra water is pulled into the muscle, increasing cell volume.
The increased cell volume generated by the NKCC pump is driven by the sodium gradient created by the Na+/K+ ATPase pump.
As stated above, the extracellular sodium gradient created by the sodium-potassium ATPase pump not only increases cell volume, it also drives amino acid uptake inside the cell, turning on protein synthesis and repairing damaged muscle. Once again, while all of the essential amino acids activate protein synthesis to a certain extent, leucine is the most potent trigger, which is transported through this TAT mechanism.

Training turns on protein synthesis and protein degradation, and the amount of new size and strength there is to gain is based on the ability to consistently shift the balance toward protein synthesis and away from protein breakdown after every single workout. Because protein turnover increases substantially in the minutes to hours after training, maximizing cell volume with optimal workout nutrition is critical to long-term progress.
To kick-start the muscle growth/repair process after training, we need to get leucine inside the cell, which is driven by cell volume, dependent on the sodium gradient induced by the sodium-potassium ATPase pump.
At the most basic level, both increased cell volume and amino acid uptake are dependent on sodium, potassium, ATP, and water.

Practical Application

Properly Timed Workout Nutrition
By this point it’s obvious that nutrient timing around the workout period can make or break your ability to recover and improve.
Amino acids are osmolytes that pull in additional water when transported into cells increasing cell volume.
Insulin activates amino acid transport, and also increases cell volume by inducing glucose uptake. While macronutrient timing is important, there are additional considerations to be made in order to maximize intra-workout cell volume potential:

Pre-Workout (~45 minutes before)
Functional carbs such as highly-branched cyclic dextrin will keep insulin levels steady along with fast-acting protein hydrolysates.
To maximize cell volume, sodium, water, and to a lesser extent, potassium, magnesium, and calcium are all important here as well.
The sodium-potassium ATPase pump creates the extracellular sodium gradient that makes cell volumization, amino acid uptake, and even glucose uptake possible. Although you should be properly hydrated well in-advance of the workout, water intake should be further increased during this time.
Protein: 30-50g of any medium to fast-acting protein source (ex. mixtures of whey and casein isolates/hydrolysates and concentrates). Whole-food protein is okay an hour before training, no less than a half hour before though (an hour being ideal).
Carbs: 25-75g of low to medium GI carbs (ex. a cup of oatmeal with a cup of blueberries). Carbs are optional, but should be included if you plan to train hard.

Pre-Workout (15 minutes before) and intra-workout
Functional carbs and fast-acting protein hydrolysates in liquid-form.
During this period, as well as during the actual workout, water and electrolyte intake (sodium, potassium, magnesium, and calcium) are crucial to promote maximal nutrient uptake and cell volume.
A product specifically designed for this purpose can take the guesswork out of it, one that contains functional carbs, and quick-acting peptides from casein hydrolysate, and is loaded with all the electrolytes required in the correct ratios to promote maximal increases in cell volume.
Creatine use is ideal here, because creatine uptake efficiency may increase in response to the increased interstitial osmolarity that causes a muscle pump during training.
Protein: 10-20g of BCAA or 20-30g of isolates/hydrolysates from casein, or whey
Carbs: 35-50g of high GI carbs, drank throughout the workout. Carbs are optional, but the insulin response from carbs may synergistically amplify protein synthesis in the presence of amino acids, while also a powerfully inhibiting protein degradation.
There's a fat-burning advantage to keeping insulin low for those who are pre-contest or are insulin resistant, in which case it may be best to omit carbs here, however, the insulin response can be very helpful for those strictly looking to put on size.

Post-workout (within 60 minutes after)
Protein hydrolysates to promote continued protein synthesis, and from a cell volume standpoint continued water and electrolytes consumption, followed by rest.
EAA intake during the pre-and intra-workout periods pays off bigtime in the post-workout period by increasing the expression of amino acid transporters (System A and System L – which happens at the ‘post-transcriptional level’, where existing mRNA’s are translated into proteins), priming the cell for maximum amino acid uptake and activation of protein synthesis, allowing cells to rapidly increase the level of particular proteins when needed.
This is why fast-absorbing protein isolates or hydrolysates during the pre-and intra-workout periods are ideal.
Protein: 30-50g fast-acting protein, whey isolates/hydrolysates, or casein hydrolysate
Carbs: 25-75g of medium-to low GI carbs, depending on the individual, their goals, and phase of training. Off-season lifters or hard-gainers can get away with 50-100g of a mixture of medium to high GI carbs. Carbs are optional, but highly advised unless drastic fat reduction is needed.
True hard-gainers can really benefit from the protein degradation inhibiting effects of insulin here. The big spike in insulin from the high GI carbs and more sustained elevation from medium GI carbs may sustain the protein synthetic response longer.
It’ ok to occasionally omit carbs altogether here for those who are pre-contest or insulin resistant people, but don't make it a habit.

Optimal cell volume, activation of protein synthesis, and inhibition of protein breakdown are all dependent on proper hydration. Even slight dehydration can impair performance, and compromise the ability to recover from intense training.

Optimize Electrolytes – Water Alone Isn't Enough
Maintaining optimal levels of osmotically active molecules (electrolytes, which function as osmolytes) such as sodium, potassium, magnesium, and to a lesser extent chloride, calcium, phosphorous, are needed to draw water into the cell and increase cell volume.
Potassium, and especially sodium, in particular are required for cell volumization and amino acid uptake (since sodium is necessary for glutamine uptake), both before and after the workout, because blood volume is highly dependent on sodium levels, meaning the ability to get, and sustain a pump while training, will be almost non-existent if you're sodium-depleted.
Regularly consuming potassium-rich foods is ideal as well – potatoes, broccoli, bananas, squash, are all excellent potassium sources.
Function of the Na+/K+ ATPase and NKCC pumps are also dependent on magnesium, meaning a deficiency will compromise cell volumization.
Water, amino acids, and electrolytes are all needed post-workout to maximize the cell volumization process that drives protein synthesis.

Creatine Monohydrate – The Original Cell Volumizer
Creatine is an important osmolyte which supports cell volumization both directly, and indirectly. Creatine is stored in muscle cells as phospho-creatine which directly increases cell volume by pulling additional water into the cell when it's absorbed, and also supplies a high-energy phosphate group to regenerate ATP during high intensity contractions, and provide the sodium-potassium ATPase pump with the energy needed (in the form of ATP) to move sodium outside the cell against its concentration gradient which facilitates cell volume indirectly. This function is so important for life itself that upwards of 30% of total cellular ATP is used just to keep the sodium-potassium ATPase pump running.
5 grams a day is all that is needed.

Glutamine Loading
Glutamine increases glycogen synthesis and inhibits protein breakdown, and glutamine uptake into the cell causes cell volumization, which primes muscle cells for protein synthesis because a full/volumized muscle is an anabolic muscle.
Protein synthesis is limited by glutamine depletion. After an intense training session, an inflammatory response is mounted, which allows immune cells to traffic into thrashed muscle tissue to begin the repair/rebuilding process.
Glutamine is rapidly taken up by immune cells, which is why it's considered the ‘fuel of the immune system’, and is also why plasma glutamine is depleted following intensive training.
Since glutamine requirements are elevated in the post-workout period, and the local immune response may be competing for the availability of glutamine to prime muscle cells for amino acid uptake and protein synthesis, pre-loading cells with glutamine may reduce the ‘lag-time’ associated with leucine-activation of protein synthesis.
10-15g of glutamine or glutamine peptides immediately post-workout, along with BCAA’s since they increase muscle glutamine production (BCAAs and leucine are also useful during the pre-workout period to help maximize endogenous glutamine production), is all that is needed.

The Insulin Connection
Along with directly activating protein synthesis, insulin also increases translocation of the System A amino acid transporters to the cell membrane, meaning that insulin causes more System A transporters to be displayed on the cell membrane, ready to drive more glutamine into the cell, which leads to more cell volume, which drives more leucine into the cell, and ultimately contributes to greater protein synthesis.
While EAAs increase the expression of amino acid transporters, it's the insulin signal that allows them to be displayed on the cell surface, ready to shuttle new amino acids into the cell.
This is yet another reason why pre-and intra-workout carbs are a good idea unless you're in extreme fat loss mode, as insulin increases the capacity for cellular amino acid transport.

Insulin–Potentiating Amino Acids
Certain amino acids (ex. glutamine) can be used to potentiate insulin release. Glutamine is a powerful activator of ‘incretin’ hormones, which make insulin-producing cells in the pancreas more sensitive to glucose. Glycine is another that potentiates insulin release, but through a different mechanism.
Although post-workout carbs alone will increase insulin levels, combining these insulin-potentiating amino acids with carbs will supercharge the pancreas for a greater insulin release. While it's best to keep insulin levels on the lower side most of the time, increased insulin levels in the intra-workout period maximizes amino acid transport, cell volume, and protein synthesis, while also suppressing protein breakdown.

Beta-Alanine To Buffer Lactate Production
The type of training geared towards building muscle produces considerable amounts of lactate, which lowers muscle pH, results in early muscle fatigue and weakness, reduced amino acid uptake (which suppresses mTOR activation of protein synthesis), and inhibits certain amino acid transporters, including System A, increasing protein breakdown.
Beta-alanine increases muscle carnosine levels and acts as a natural acid buffer, extending anaerobic threshold by limiting the reduction in muscle pH from training, and also helps maintain, and kick-start protein synthesis after intense training by preventing the attenuation of amino acid transport.

Maximize Mechanical Tension To Create A Highly Anabolic State
While cell volumization is a fundamental driver of muscle growth and recovery, the volumized muscle still needs to be placed under a great deal of mechanical tension because part of the mechanism by which cell swelling activates protein synthesis is through increased tension on the cytoskeleton which directly increases protein synthesis by enhancing mRNA translational efficiency. High-intensity muscle contractions directly activates/increases amino acid uptake and protein synthesis, in part by activating the sodium-potassium ATPase pump.

Nutrient Wrap-Up
Nutrients have a potent effect on the protein synthetic response, and timing them right can make or break your training progress.
During intense training sessions, protein synthesis is reduced and protein degradation is activated. The extent to which we can minimize the catabolic effects of training and the quicker we can return to ‘anabolic mode’ during the post- training period ultimately determines how efficiently we'll recover and grow.
Macronutrient timing is important, but it is a means to an end. Cell volume is the main driver of amino acid transport and protein synthesis. By understanding how amino acid transport happens and how it's regulated by cell volume we can get more leucine into trashed muscle cells faster, thereby stoking the anabolic fire and ultimately leading to better gains.

If you have any questions about any of the strategies presented in this article, feel free to contact me at ben@paramounttraining.ca. I'm available for online consulting and personalized program design, as well as one on one training if you are located in the Greater Toronto Area (GTA).

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