Muscle Protein Synthesis – What You NEED to Know

Within in the fitness community, there are a few topics that everyone loves to talk almost endlessly about; training frequency, muscle damage, macronutrient numbers and muscle protein synthesis…

Everyday it seems that I am answering questions regarding these topics, either in person or online.

Today I’m here to focus on one of those topics in particular… Muscle Protein Synthesis!

Rather than consistently saying the same thing over and over again, I have compiled this article in order to 1) direct my clients to for further information if they want to know some of the details, as opposed to the more general knowledge I can pass on during a training-session, and 2) help spread some sound information to those who aren’t fortunate to train with the walls of a JPS facility.

Here is a graph I created in order to try help people visualise these concepts, and understand the balance between Muscle Protein Synthesis and Muscle Protein Breakdown over a period of time. Which is important to understand, the first lesson is, don’t think of things in an acute sense. Think broadly and long term.


Before I dive in, it’s important to know that ALL the protein you eat does in fact, get “absorbed” by your body. There is no 30g limit or something like that, where your body stops absorbing protein after a certain point. However, where this idea/myth comes from, is that not all protein is utilized by your skeletal muscles for the purpose of anabolism (growth). An important point to remember is that your body’s primary purpose, its number one priority, at all times and at any cost: STAY ALIVE! Not build slap of muscle… And as such, a large portion of the protein you eat, is directed towards your internal organs (gut, liver etc) after digestion.

In saying this, eating in between 1.6-2.2g of protein per kg of bodyweight per day without even worrying about the following factors/information, will get you close to maximising muscle growth. But, if you are someone who wants optimization – either for yourself or for your clients – then the details must also be taken care of. Either way, it is good to have at least a basic understanding about the following.

The anabolic or catabolic actions and outcomes of any cell, is dependent upon net protein balance, (NPB) and muscle cells (fibres) are no different. NPB is the outcome of two factors; the processes of muscle protein synthesis and muscle protein breakdown. The difference between both processes (MPS minus MPB) results in NPB. For example, when MPS is elevated, MPB is still present but on the net balance a greater amount of MPS is occurring – positive NPB.

Both of these processes are sensitive and will respond to aminoacidemia (a high level of amino acids in the blood) which occurs after a protein containing meal is ingested, as well as high levels of muscular tension, which we impose through the means of resistance training. Both these factors increase the anabolic activity within a muscle cell and down regulate catabolic activity. The result is a shift in NPB towards a positive state; resulting in growth of the muscle cell over time, provided both nutritional and exercise factors are applied consistently.

Regarding nutrition, a minimum of 20g high quality protein that consists of all essential amino acids must be consumed to maximise MPS. Low quality protein sources will fail to stimulate MPS to the same degree as higher quality sources, either in magnitude of stimulation or duration. This is because the stimulation of MPS from protein consumption is driven by the presence of all the essential amino acids, but primarily leucine. If the protein bolus does not contain 2-3g of leucine, MPS will not be maximally stimulated. It is also worth knowing that further leucine consumption above this threshold does not provide any further stimulation of MPS.


The elevation in MPS is transient (lasts for typically 2-3 hours but is dependent on total calorie and macronutrient consumption of the meal) and will reach its highest point around 100min into the postprandial period (time after the meal). Any additional protein beyond what is needed for maximisation will only have diminishing returns on MPS due to the decreasing sensitivity of skeletal muscle – this is referred to as the muscle full effect.

Muscle full effect: Skeletal muscle will enter a refractory state and become insensitive to additional protein consumption once MPS has been “turned on”. The level of insensitivity is dose dependent, meaning that the more protein you consume, the more insensitive your muscles will become. Even if additional protein is consumed during this time, MPS will still return to baseline at its usual rate of 2-3 hours (likely to be an evolutionary trait, as high levels of MPS is energetically costly to the body and it makes sense for the body to try to shut down energy costly processes quickly. This is what helped prevent us from starving as cave men all those years ago).

From an exercise standpoint, Resistance training results in an increase in localized (muscle group specific) MPB due to the microscopic tears that occur in the fibres, as a result of hard training. However, a more important by-product of resistance training is the elevation in MPS that is independent of nutrition, which lasts 24-48 hours (depending on a few factors, such as the training age of the individual and the difficulty of the session). However, if protein is not consumed at any time during the post workout period, NPB will remain at a negative due to the default activation of MPB.

If protein IS consumed within the post workout period, then there will be a ‘double whammy’ impact on MPS (combination of resistance training and aminoacidemia) resulting in an elongated state of positive NPB. This is due to the fact that resistance training sensitizes skeletal muscle to hyper-aminoacidemia. This means that the capacity for amino acids to be used for the synthesis of muscle tissue is increased, resulting in a higher intake of protein that is required in order to maximise MPS (the ceiling moves up and protein consumption should move up).

However, studies show that MPS only rises a further 20% when double the protein is consumed after a full body workout (20g vs 40g). Even though 20% isn’t an overly large increase, additional protein consumption up to 40g post workout is recommended, if maximising growth is a concern. Do remember though, the muscle full effect still appears to exist in the post workout period (approximately 40g).

Consuming carbohydrates immediately post workout is also a highly popularized method, which is done so for the purpose of ‘spiking insulin’ to increase the anabolic response through greater MPS rates. However, in the grand scheme of things, the importance of an insulin spike via immediate carbohydrate consumption post workout becomes greatly diminished when sufficient protein is consumed.

The co-ingestion of carbohydrates during the post workout state does not further stimulate MPS if adequate protein is ingested (approximately 40g or 0.4g per kg of bodyweight). Insulin needs to be injected to supraphysiological levels (beyond natural limits) in order for it to result in an increase in MPS. The amount of insulin that is produced from a standard carbohydrate serving (15-30mU/l) is not mandatory for MPS stimulation and only has a minor impact on muscle anabolism, via its role in in reducing muscle catabolism and inhibiting MPB – not increasing MPS.

In saying this, when a mixed meal including carbohydrates is consumed, insulins suppression effect on MPB occurs within 2 hours postprandially and insulin levels stay elevated for 3-6 hours depending on the size of the meal. With this information we can conclude that carbohydrate consumption 1-2 hours pre workout will negate the need for an immediate insulin spike in the post workout state. Overall, the consumption of carbohydrates in the post workout state should depend on timing of the pre workout meal followed by preference and convenience.

It is also worth knowing that protein itself is insulinogenic, due to insulin’s job being to transport glucose AND amino acids into cells. Whey protein in particular is highly insulinogenic and has the potential to both stimulate MPS and suppress MPB due to the presence of all essential amino acids. Thus we can see that adding carbohydrates to a whey protein shake is unnecessary.

The need for a post workout insulin spike becomes relevant in the absence of a pre workout meal or more importantly in a fasted state. Training fasted, without paying any attention to nutrient consumption and timing won’t matter if you only do it occasionally. However, if fasted training with a poor nutrition intervention is of regular occurrence, then muscle growth will likely be impaired.

During fasted training, NPB is negative because MPB exceeds MPS. This is due to several reasons:

  1. The direct micro damage of muscle fibres leading to MPB.
  2. If muscle glycogen levels are low, endogenous (internally stored) amino acids may be oxidised to form glucose (through gluconeogenesis) for glycogen resynthesis and optimal muscle contractions.
  3. If muscle glycogen levels are low, intracellular anabolic signalling can be negatively impacted…AMPK (cells energy sensor) will inhibit energy consuming processes including mTOR (muscles anabolic signal) and will amplify catabolic processes like protein breakdown.

For the above reasons, resistance training in a fasted state is acutely catabolic which makes nutrient consumption increasingly important if optimal muscle growth is the goal. When training fasted, consuming a mixed meal of protein and carbohydrate in the post workout state is definitely recommended to reverse catabolic signals and activate MPS. With this being said, the best option would be to consume 20-30g of whey protein in the pre workout state to decrease the urgency and need of a post workout meal.

That, is a slightly more in-depth look at protein synthesis and how you can learn to maximise it over the day. I hope you found this interesting or useful and if you’d like more content like this, then feel free to leave a comment or send me a message so I can try answer any questions you may have!





author: Martin Refalo

Martin Refalo is a competitive bodybuilder and body composition coach at JPS Airport West. With a bachelor of exercise science and passion for knowing the in's and out's of fat loss and muscle gain, Martin is fast becoming one of Melbourne's leading physique coaches.