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The Link Between Genetics and Muscle Growth

Reading Time: 6 minutes 32 seconds


DATE: 2023-09-05

Science is opening new doors to understanding how our genes impact all areas of our lives. It has long been known that genetics impacts health, and it seemed safe to assume it also determines some of our fitness abilities. Not all of us are destined to be elite athletes, no matter how hard we train.

Now researchers know for sure certain genes impact how far we can go in fitness, endurance, athletics, and strength. Genetics impacts all areas of fitness and performance, including muscles and strength.

From sprinters who have genes allowing them to develop more fast-twitch muscle fiber to endurance runners with genetics dictating muscle contraction speeds, genes determine our abilities to some degree.

As a personal trainer, you will encounter clients who struggle to develop muscle strength and size and those who excel at it. You may also be increasingly expected to turn to genetic test results to help clients maximize their potential. With a better understanding of how genes impact muscle growth and development, you can improve client workouts and results.

Yes, There Are Genes That Impact Muscle Growth

In fact, there are several genes that affect muscle development and growth. Scientists have discovered many genes involved in muscle growth. How they are involved is complicated and not yet fully understood. And more genes that affect muscle growth are likely to be discovered in the future.

A big list of genes is known now to trigger muscle growth. For instance, in one study researchers looked at, the manipulation of over 40 genes in laboratory mice and found that they all increased hypertrophy in skeletal muscle. They found that three genes in particular—Asb15, Klf10, and Tpt1—were most highly expressed in muscle tissue (1).

Can Genetics Affect Muscle Growth and Decline as Well?

Genes can also be involved in the decline of muscle tissue and strength. For example, the gene MSTN codes for a protein known as myostatin. Found mostly in muscle tissue, this protein is responsible for restraining muscle growth. A rare condition caused by a mutation in MSTN causes an overgrowth of muscle and abnormal hypertrophy (2).

Testosterone and Muscle Decline

One of the most important genetic factors that trigger declines in muscle tissue is the one regulating testosterone. When this hormone decreases, muscle mass becomes more difficult to develop and loss of tissue and strength can result. Low testosterone can be caused by medical conditions but is also a natural part of aging. Genes that regulate testosterone indirectly impact muscle tissue.

Can Genetics Affect Muscle Growth to the Extent that It is Impossible to Make Gains?

Unless you have a client with a rare and serious genetic disorder, it will always be possible to help them make muscle gains. The differences between most individuals in good health are not that great. Some of your clients will gain strength easily with a couple of sessions per week, while others will need to train harder and watch their diets more to see the same results.

Genetic Measures That Inform Strength Training

For clients who have undergone genetic testing, you can use the results to design better workouts, to set more appropriate fitness goals, and to motivate your clients to work toward them. For health and fitness, genetic tests provide a few pieces of information that are important for muscle growth and strength training:

Enhanced Weight Loss Genotype

For weight loss, fitness and health DNA tests give results ranging from low to enhanced. This rating gives you a lot of information about how a client gains or loses weight, responds to macronutrients, and changes body composition.

With respect to muscle mass, an enhanced genotype means strength training is essential. A client with this genotype and weight loss goals runs the risk of losing muscle mass without weightlifting or other strength exercises.

These clients also need to watch protein in the diet and eat enough to minimize muscle loss. For anyone doing strength training, it is important to plan diet and exercise to maximize fat loss and reduce the risk of losing muscle tissue. For clients with an enhanced genotype, adding protein to the diet in the right amounts is especially important.

Body Composition Genes

For these genes, your client will get a rating of below average, normal, or enhanced. The body composition test looks at a long list of genes related to how the ratio of fat to muscle tissue responds to strength training. Your enhanced clients will have the greatest response and find it easier to build muscle mass with proper training. Most people fall into the normal category.

Testosterone Levels

Testosterone is a hormone that plays a role in muscle growth. Men have much more of this hormone than women, which is why they develop strength and build muscle mass more easily. A genetic test of fitness and health will rate an individual as more likely, normal, or less likely.

The clients you should be concerned about are those rated as more likely. This means they are more likely to experience low testosterone levels.

Developing Strength Goals Based on Genetics

Whether or not your client undergoes a DNA test, you may be able to determine some of their genetic tendencies relative to strength training, and that can help you set better goals together. If they have gotten a test and you have some of the results, this will make goal setting a little easier.

Discuss genetic results with your client and what their specific measures mean for strength training. This helps set realistic expectations and informs the goals they can reasonably achieve.

For example, if you have a client with a below average rating for body composition, they will struggle with building muscle and losing fat. With this information, you can set a body composition goal that makes sense for them and that may be less ambitious than what you would set for another client.

Designing Training Sessions and Motivating Clients

Once you have goals in place, use the genetic information to design more effective, appropriate workouts for your client. Understanding a client's genetic factors and predispositions can also help with motivation. Expectations are important. If a client wants to look like a bodybuilder but has genes that make muscle building difficult, you need to help them adjust their expectations. Focus on health and making progress for motivation rather than an impossible goal.

Training Based on Weight Loss Genotypes

Whether your clients are interested in weight loss or not, their genotype can help you plan more successful training sessions. For instance, people with a low or below average genotype may not respond well to intense exercise. Using resistance training for both strength and cardio is a good strategy for these individuals.

Clients in the normal or enhanced range will see more results from higher-intensity workouts, both cardio and strength training. With these clients, you can really focus on strength development and hypertrophy.

Training by Body Composition Type

In considering clients with varying abilities to achieve and maintain a healthy body composition, you'll see results ranging from enhanced to below average, but most will be normal. Enhanced clients benefit from a focus on strength training. Two to three days per week is recommended. You will need to mix up exercises and challenge these clients in new ways.

For clients with a normal body composition type, two days per week of strength training is usually adequate. They will need more cardio than the enhanced group to lose fat. For below average clients, do strength training two to three times per week. Focus on heavier weights to help boost metabolism and burn fat. Both normal and below average clients benefit from one powerlifting session per week.

Regardless of the genotype of your client, everyone should be doing strength training at least twice per week. Once a week is not enough to get the benefits.

Working with Clients with Lower Testosterone

Clients with results that indicate they are more likely to have low testosterone levels are going to struggle more with muscle building. Testosterone also declines with age, so your male clients over 45 will naturally have this limitation as well.

If you have a client with low testosterone on a genetic test, consider recommending they see their doctor for further testing. Some underlying health conditions can cause low testosterone, and they should be addressed and managed.

Whether your client has a condition or just tends to have lower testosterone, you can include certain types of training and make lifestyle recommendations that support healthy levels. For instance, doing total body strength training is the best type of strength work for improving testosterone production. For cardio, high-intensity interval workouts are best.

Lifestyle habits especially important for these clients include getting adequate sleep. The body produces many of its hormones during sleep. Furthermore, lack of sleep can deplete testosterone levels. Excessive alcohol consumption also interferes with testosterone production, so encourage these clients to cut back on drinking.

Genetic-Based Fitness Training

Genetic-based training will become more common as research continues to unlock the secrets of our DNA. With testing more accessible than ever before, individuals have a greater opportunity to learn about their own strengths and weaknesses. As a trainer, you can use this information to make goals, training, and motivation more personalized and more effective for your clients.

Interested in learning more about training based on genetics? Become a DNA-Based Fitness Coach with the ISSA's newest certification course.


  1. Verbrugge, S.A., Schonfelder, M., Becker, L., Fakhreddin, Y.N., de Angelis, M.H., and Wackerhage, H. (2018). Genes Whose Gain or Loss-of-Function Increases Skeletal Muscle Mass in Mice: A Systematic Literature Review. Front. Physiol.9:553. doi: 10.3389/fphys.2018.00553. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5992403/

  2. National Institutes of Health. U.S. National Library of Medicine. (2020, January 7). MSTN Gene. Retrieved from https://ghr.nlm.nih.gov/gene/MSTN#conditions

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