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ISSA, International Sports Sciences Association, Certified Personal Trainer, ISSAonline, Muscle Protein Synthesis: What It Is and How to Maximize It

Muscle Protein Synthesis: What It Is and How to Maximize It

Reading Time: 5 minutes 30 seconds


DATE: 2022-12-20

If your client wants maximum muscle growth, resistance exercise is a must. Yet, creating a training program that effectively increases muscle strength and size requires that you fully understand these soft tissues. This enables you to develop a regimen that works with the body’s natural processes. In turn, it leads to better results. 

One of these bodily processes is called muscle protein synthesis. To appreciate what effect protein synthesis rates can have on muscle growth first requires that you know a little bit about protein itself.

It All Starts with Protein

Skeletal muscle cannot function without protein. One reason is because it wouldn’t have the energy it needs. Each gram of dietary protein supplies the body four kilocalories of energy. Yes, energy can also be derived from carbohydrates and fat. But protein has something that both of these other macronutrients lack. It has amino acids. 

What do you get when you connect one amino acid to another amino acid? You get a peptide, also sometimes referred to as a peptide chain. This amino acid chain is the primary structure of protein. And if you break muscle fiber down, you find two protein filaments: actin and myosin. Thus, protein is the structural foundation of muscle. As such, muscle also cannot grow without it. 

Typically, we think of keeping our muscle protein stores full via our diet. But what many people fail to realize is that our bodies can create protein as well. When this process occurs in the muscle, it is called muscle protein synthesis.

What is Muscle Protein Synthesis?

In simple terms, muscle protein synthesis is the way in which the body turns amino acid chains into muscle protein. This is important because we are always experiencing some level of protein turnover. 

Protein turnover is similar to how our body is constantly replacing our skin cells. If you pay attention, you will notice that old skin cells are continuously flaking off. We are then left with healthier-looking skin as the newer cells are exposed. 

In the case of muscle protein, this protein in the muscle is either breaking down or building up. So, protein turnover refers to muscle protein breakdown and muscle protein synthesis (protein production) rates.

Research reveals that active people have a skeletal muscle protein turnover rate of around 1.2 percent per day. If the body breaks down more muscle protein than it creates, muscle size will shrink versus grow. What factors can lead to a breakdown in muscle protein?

Causes of Muscle Protein Breakdown

One factor that can cause muscle protein breakdown to speed up is when the body is in a fasted state. According to a 2012 study, fasting reduces protein synthesis and increases protein breakdown. In short, the muscle breaks down at a faster rate when you’re not taking in any calories. This results in a slower protein production (muscle protein synthesis) rate.

Studies also show that protein degradation increases with exercise. As the muscle protein breaks down, more protein is needed to repair the damage. When protein breakdown occurs faster than protein synthesis, muscle size and strength can decline. The net result is muscle loss.

If muscle mass is negatively impacted by protein breakdown occurring faster than protein synthesis, can you achieve muscle growth by reversing these two factors? The answer is yes.

The Connection Between Strength Training, Protein Synthesis, and Muscle Growth

When muscle protein synthesis occurs at a faster rate than protein breakdown, muscle is able to grow. Muscle cell growth is referred to as muscle hypertrophy.

Muscle hypertrophy is commonly achieved with resistance training. The more weight you lift, the bigger your muscles become. But doesn’t this directly contradict the fact that skeletal muscle protein synthesis slows with exercise? Not exactly.

Interestingly, some pieces of research have found that resistance exercise boosts muscle protein levels. And these levels remain elevated up to 48 hours post-workout. This study further noted that effect was even greater if 10 grams of protein were consumed immediately after the exercise session.

This supports the notion that strength training stimulates protein synthesis. It also suggests that it stimulates it even more when protein ingestion occurs directly after the workout has ended.

Recommended Protein Intake for Boosting Muscle Mass

The amount of protein a client should consume depends on a variety of factors. These include:

  • activity level – engaging in vigorous cardio and resistance exercise require more protein

  • body weight – the more you weigh, the more protein you need 

  • fitness goals – protein assists with both weight loss and increased muscle mass

The Academy of Nutrition and Dietetics recommend that protein intake be between 1.2 and 2 grams per kilogram of body weight per day. If engaging in intense physical exercise, a higher intake is likely required. Higher intake is also recommended when an injury exists to help prevent muscle loss.  

The Academy further stresses that protein intake should be spread out over the course of the day. This provides the muscle the protein it needs in a steady supply. That said, 0.3 grams of protein per kilogram of body weight should be consumed immediately after working out.

High Protein Foods vs Protein Supplement: Which Is Best?

There are two ways to increase protein intake. One option is to eat more protein-rich foods. The other is to take a protein supplement, such as a protein powder. Which protein source is better for building lean muscle? It’s easy to make an argument for both. 

Consuming more food-based protein sources helps satisfy hunger while supporting skeletal muscle growth. Clients often feel less hungry when eating a high protein diet. Unhealthy cravings are reduced. This makes it easier to make better food choices. They also typically feel more energetic.

That said, some people struggle with getting their recommended protein intake. This is especially true for clients who’ve cut meat, eggs, and dairy from their diet. People following a plant-based diet may need a protein supplement to ensure they get enough.

Either way, it’s important to choose high-quality protein sources. Foods that fall into this category include lean meat, poultry, eggs, Greek yogurt, and cottage cheese. In the case of supplements, whey protein is usually a better choice. This is partially because whey protein is digested quickly. It gives the muscle an immediate protein boost post-workout. 

Another supplement to consider is a branched chain amino acid (BCAA) supplement. Studies have found that BCAAs increase the muscle protein synthesis rate. Thus, this is one more way to increase the growth of skeletal muscle tissue.

Check out this ISSA blog on the role of amino acids in fitness. Learn about essential amino acids and branched chain amino acids such as valine, leucine, and isoleucine. 

A Final Word About Muscle Protein Synthesis

It’s important to note that muscle protein synthesis rates have a genetic component as well. One way to better understand how a client’s genes could be impacting their workout results is with genetic testing. 

For example, a person with a “normal” protein utilization genotype will likely get more benefit from eating a diet that is 15 to 30 percent protein. A client with an “enhanced” genotype may get better results aiming for a protein intake around 25 to 35 percent.

The ISSA offers DNA-Based Fitness Coach certification. This course teaches you how to interpret clients’ genetic tests as they relate to diet and exercise. This enables you to create a program that works with their genetic tendencies, allowing them to achieve the results they want faster and with less frustration.


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  2. Vendelbo, M., Jorgensen, J., Jessen, N., & Moller, N. (2012, May 1). Protein metabolism in human skeletal muscle after 72 h fasting; increased muscle protein breakdown and impaired insulin signaling. Endocrine Abstracts. Retrieved December 2, 2022, from https://www.endocrine-abstracts.org/ea/0029/ea0029p1163 

  3. Tipton, K. D., Hamilton, D. L., & Gallagher, I. J. (2018). Assessing the Role of Muscle Protein Breakdown in Response to Nutrition and Exercise in Humans. Sports Medicine (Auckland, N.Z.), 48(Suppl 1), 53–64. https://doi.org/10.1007/s40279-017-0845-5

  4. Weinert D. J. (2009). Nutrition and muscle protein synthesis: a descriptive review. The Journal of the Canadian Chiropractic Association, 53(3), 186–193.

  5. Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Position of the Academy of Nutrition and Dietetics, dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528. https://doi.org/10.1016/j.jand.2015.12.006 

  6. Jackman, S. R., Witard, O. C., Philp, A., Wallis, G. A., Baar, K., & Tipton, K. D. (2017). Branched-chain amino acid ingestion stimulates muscle myofibrillar protein synthesis following resistance exercise in humans. Frontiers in Physiology, 8. https://doi.org/10.3389/fphys.2017.00390 

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