Tyler Robbins Fitness

B.Sc. Biochemistry, Certified Strength and Conditioning Specialist (CSCS), Certified CrossFit Trainer (CCFT/CF-L3), USA Weightlifting Level 1

Filtering by Tag: Genetics Series

Genetics Series: Muscular Size

Being in the fitness industry, I hear the same goals and aspirations all the time:

Females: "I don't want to get too bulky!"

Males: "I want bigger muscles!"

Obviously this is a generalization, because I am sure there are plenty of women whose goal is to increase the size of their muscles, and plenty of men who wish to stay lean rather than get "bulky." What this blog will hopefully inform you is that regardless of your goals, much of your size and strength is already genetically pre-determined and you won't be able to do much about changing that.

I'll explain.

I'm sure I could write many blogs on the social significance of how we are raised, about what an ideal man or woman looks like. How entertainment, the media, professional athletes, etc. all shape the way we perceive the ideal physique should look like. Truth is, many of the professionals you see - whether they are athletes, actors, or models, are either genetically prone to look the way they look, or have had some *ahem* pharmaceutical help to assist their transformation.

I know, I know, this sounds like a whiny cop-out excuse to success. Don't get me wrong, I know that hard work pays off. I advocate hard work and effort to my clients and followers every single day. That is not what I'm saying here. But just as stretching yourself every single day isn't going to make you any taller, training a certain way because someone told you to isn't necessarily going to get your the big huge muscles you think you want. That is the primary focus of this Genetics Series.

Going beyond the hormonal differences between men and women, and the difficulty for most men, let alone women, to grow any measurable amounts of muscle, there are vast differences in the determination and makeup of our muscles. Case in point:

Genetic determinism of fiber type proportion in human skeletal muscle.


Skeletal muscle fiber type distribution is quite heterogeneous, with about 25% of North American Caucasian men and women having either less than 35% or more than 65% of type I fiber in their vastus lateralis muscle. To what extent human skeletal muscle fiber type proportion is under the control of genetic factors is examined in this paper. The results summarized here suggest that about 15% of the total variance in the proportion of type I muscle fibers in human is explained by the error component related to muscle sampling and technical variance, that about 40% of the phenotype variance is influenced by environmental factors, and the remaining variance (about 45%) is associated with inherited factors. These estimates suggest that a difference of about 30% in type I fibers among individuals could be explained exclusively by differences in the local environment and level of muscular contractile activity. However, unidentified genetic factors would have to be invoked to account for the observation that the skeletal muscle of about 25% of the North American Caucasian population have either less than 35% or more than 65% of type I fibers.

This study found a 45% variance in muscle fiber distribution from genetic factors. For those of you unaware, type-I muscle fibers are considered "slow-twitch." They don't generate as much force as type-II fibers, tend to be more "aerobic" in nature, or in other words, they can contract for longer periods of time since they don't generate as much force. Elite marathon runners, for example, tend to have higher ratios of type-I to type-II muscle fibers.

On the other hand, type-II muscle fibers ("fast-twitch") generate more force, but can't contract for as long, or for as many repetitions as type-I muscle fibers. Elite strength and power athletes tend to have a greater ratio of type-II to type-I muscle fibers. Type-II muscle fibers have the greatest affinity for muscular hypertrophy or growth. Type-I fibers can enlarge, but not to the extent of type-II fibers. Strength athletes and bodybuilders have larger muscles for this very reason.

So, as the above study found, genetic variance plays a large role in the ratio of type-I to type-II muscle fibers, and can therefore determine not only the strength and performance of said muscles, but also the size of them too.

This study actually focused on creating and testing workout programs specifically designed for genotypes. What they found is exactly what we would expect - participants who are more well-suited for a specific training stimulus based on their genes saw greater results.

The takeaway? Well, not everyone is able to, or should even worry about a genetic test just to determine their optimal training program. Most of you reading this will probably already have a pretty good understanding of what works for you. Some folks are good runners. Some are not. Some lift weights with ease, while others struggle. Regardless of your current situation, however, focus on improving you and stop comparing yourself to others, regardless of how similar you think you may be to someone else.

Key points to focus on:

  • Size isn't necessarily better - bigger muscles aren't necessarily stronger, so even if you can't build big muscles doesn't mean you can't be strong, relative to your size.
  • Your body frame is a pretty good indicator of the size of your muscles and the strength you can gain. If you have big, broad shoulders, for example, you are more likely to also have large, strong muscles.
  • Despite your genetic advantages or disadvantages, hard work will always improve your current situation.


A couple key points can be summarized from this type of research. First, we know that certain individuals have a greater affinity for muscular growth due to a number of reasons, including their ratio of type-II to type-I muscle fibers, genetic potential for growth, hormonal response, etc.

Changing gears a bit, however, we can also begin to understand the differences in training stimuli and how they affect hypertrophy. Research that tries to understand optimal hypertrophy training styles are quite variable. If there was a one-size-fits-all approach to training, then research would be far more specific in its findings. For example, lower intensity, higher repetition training may be more beneficial for some individuals whereas higher intensity, lower repetition training may be more beneficial for others. What works well for you may not work well for me.

It is impossible to eliminate all variables when it comes to scientific studies, especially genetic variations. That is why whenever you hear of a health study, the results are presented as percentages or trends. Unfortunately, at times, media outlets like to sensationalize headlines. This results in many jumping to conclusions and taking something as truth, rather than understanding that results need to be generalized and applied to a broad populous.

This is applicable to fitness professionals as well. Just because an individual has large muscles or "looks the part" when it comes to training doesn't necessarily mean they are well-suited to coach another individual on how to duplicate those results. They have found an optimal training style that has helped them personally strive for their goals - be it muscular growth, however that does not mean that what worked well for them would also work well for you. Also, be weary of coaches or fitness professionals who paint a broad stroke, offering fitness plans and/or diet plans that is applicable to the masses. Every individual is different, goals are different, health status is different, genetics are different. A well-rounded coach should be one that is educated and stays up-to-date with current trends and research to offer you the most optimal training and nutritional planning.

Genetics Series: Strength and Power

My old boss used to say, "You know, God made us (humans) all about the same." Sure, it is often said that humans, when compared genetically, are about 99.9% similar, however there are still some pretty remarkable variances between how we look and perform.

The 99.9% similarities between us controls things as common as having skin, hair, teeth, a stomach, high-level brains, etc., but can had differences in how those things look and work. For example, how tall we are, how long our limbs are, how big our noses are, etc. We also mostly act the same too - although this is heavily influenced by your surroundings.

If you keep looking deeper into that rabbit hole you can begin to understand that not only do our muscles oftentimes look differently, but they can act and perform differently as well. I always say to people, "You can't choose your parents," because your genetic lineage can have a drastic outcome on all of these factors that influence you. Some folks are able to build big muscles. It just comes easy (easier) to them. 

So what about athleticism? Do you remember growing up and playing with your friends? Do you remember that one friend of yours that just seemed to be better than everyone else at everything (or most things)? They could run faster, jump higher, were better at Mario Kart, and could be the best with little to no effort at all! Was this friend in the gym spending hours a day getting bigger, faster, and stronger? Of course not, they were just gifted in ways that maybe you weren't. The effectiveness of their neural pathways were better than yours. They had better coordination, better strength, better reaction time, etc.

Why are some people so good at some things? Is it because they work harder? Is it because they are more committed? Possibly, but not necessarily.

Take this review, for example:

Genetics of muscle strength and power: polygenic profile similarity limits skeletal muscle performance.


Environmental and genetic factors influence muscle function, resulting in large variations in phenotype between individuals. Multiple genetic variants (polygenic in nature) are thought to influence exercise-related phenotypes, yet how the relevant polymorphisms combine to influence muscular strength in individuals and populations is unclear. In this analysis, 22 genetic polymorphisms were identified in the literature that have been associated with muscular strength and power phenotypes. Using typical genotype frequencies, the probability of any given individual possessing an "optimal" polygenic profile was calculated as 0.0003% for the world population. Future identification of additional polymorphisms associated with muscular strength phenotypes would most likely reduce that probability even further. To examine the genetic potential for muscular strength within a human population, a "total genotype score" was generated for each individual within a hypothetical population of one million. The population expressed high similarity in polygenic profile with no individual differing by more than seven genotypes from a typical profile. Therefore, skeletal muscle strength potential within humans appears to be limited by polygenic profile similarity. Future research should aim to replicate more genotype-phenotype associations for muscular strength, because only five common genetic polymorphisms identified to date have positive replicated findings.

So although this isn't ground-breaking or particularly new, we are starting to discover just how advantageous you may or may not be due to the genetic lottery that you have played when you were born. The above review details 22 genes (that we know of) that are beneficial for strength and power performance in individuals. In these 22 genes, the more you personally have, the greater likelihood you have to being a strength or power athlete.

There are 3 "options" when it comes to these gene phenotypes. You can either have a favourable gene expression, a neutral expression, or a negative expression. In other words, whether or not you have a specific genotype can either make you good at something, potentially bad at something, or no real positive or negative effect at all.

One well-known gene, for example, is one that encodes for the protein ACTN3 has been shown to be favourable for sprinting (in those that contain the correct gene), and can actually be favourable for endurance athletes with a mutated ACTN3 protein.

Studies have linked the fiber twitch type with ACTN3, i.e. fast twitch fiber abundant individuals carry the non-mutant gene version. Also, studies in elite athletes have shown that the ACTN3 gene may influence athletic performance. While the non-mutant version of the gene is associated with sprint performance, the mutant version is associated with endurance.

What's notable in the above review is that the researchers calculated 0.003% of the population to have "optimal" gene expression for strength and power attributes. This certainly makes sense, especially in a country like Canada - population around 30,000,000, that about 9,000 individuals (give or take) have more optimal strength and power characteristics.

Does this mean that other individuals can't be strong and powerful? Absolutely not, but those individuals with favourable genetic phenotypes are certainly at an advantage when it comes to producing strength and power. On the flip side of that coin, as we have seen with ACTN3, it is entirely possible to be not all that great at something.

It should also be noted that although an individual may have a genetic potential for something, does not mean that they are going to be the best. Although this number has been associated with strength and power, let's use the same figure (for argument's sake) to discuss genetic potential for other attributes as well. Assume that even at 0.003% of the population has a genetic advantage for something, that still creates a lot of competition between yourself and the other "elites" in that category. Being strong and powerful, especially compared to your less-than-genetically-gifted friends will only take you so far. If you wanted to compete on an Olympic level, for example, then you still need to hone your skills and work hard to be even better than those around you.

I will once again remind my readers that this is not to sound like an old curmudgeon, saying that talent and athleticism is "all luck." There is certainly advantages that make some of us better than others at certain things. It is not impossible, just highly unlikely that you would see a 7 foot tall man competing at the Olympic games in weightlifting. The limb lengths and joint angles are not as advantageous for maximal torque and power required for Olympic lifting. On the other hand, although we have seen some shorter individuals play in the NBA before, the game certainly favours taller individuals. Being tall, or having a long torso (advantageous for weightlifting) cannot be trained. If, however, you are tall, and you work hard, then you have a chance to make it big.

Genetics Series: Salivary Amylase

I am going to start a new "series" of pieces here on my blog detailing the role of genetics in our appearance, performance, and health. Far too often I see individuals needlessly comparing themselves to others when in actuality, every individual is different, and even though you may appear to be similar to someone else in a lot of ways, the role your genes play in your life could be almost entirely different.

The primary purpose of this blog is to explain how these genetic differences influence much of what we can accomplish as human beings. Just because an individual can look a certain way or perform a certain way does not necessarily mean that they are a harder worker or that they have more dedication than you. Sure, hard work and dedication can improve you current situation, but it does not necessarily mean that you are going to be the best at something - despite what you may have been told.

Amylase is an enzyme that digests carbohydrates. It catalyses the hydrolysis of starch into sugars. It is released by both the pancreas and the salivary glands in your mouth. Sugary foods and beverages actually start digesting in the mouth of mammals due to the release of amylase during that first phase of digestion. Despite the fact that virtually everyone possesses an almost identical amylase gene, some individuals have more copies of the gene than others, therefore increasing their ability to produce amylase.

The following study looked to understand the relationship between amylase production and obesity.

What they found was that the individuals with the most copies (more than 9) of the amylase gene, had a lowered risk of obesity. On the other hand, individuals with fewer copies of the amylase gene (less than 4) had an increased risk of obesity. We could speculate as to the reasons why more genes are beneficial in a couple of ways.

First, increased amylase production could increase the rate of carbohydrate metabolism (digestion and absorption) right in the mouth, thereby increasing the rate at which the carbohydrates enter the bloodstream, stunting the severity and intensity of a blood sugar spike. We know that the quicker and more abrupt one's blood sugar rises, the more intense blood sugar crash may be. Wildly fluctuating blood sugar levels can lead to cravings of more sugar, so it is generally recommended that individuals consume carbohydrates that do not cause too high of a blood sugar spike. Therefore, an increase in amylase production may help to slow the overall metabolism of ingested carbohydrates by starting the process earlier (in the mouth).

Also, an increase in amylase production may also help to trigger our brains into being satiated sooner by starting the process of carbohydrate metabolism in the mouth versus waiting until the sugar reaches our intestines and absorbed into the bloodstream that way. Digested carbohydrates (glucose) are not absorbed through the stomach walls, and in fact amylase is inhibited in stomach acid, so by the time an individual consumes carbs, has them broken down in the stomach, passed on to the small intestine, and then absorbed into the bloodstream, they may have consumed far more carbs than they initially intended.

So how is this important? Well, as the first blog in this Genetics Series, we are looking to understand how different we can be as humans. Despite the fact that many of us look the same and are relatively similar, especially from a genetics standpoint, many of us interact with exercise, our diets, and world we live in in drastically different ways at times. Just because an individual is overweight or skinny, does not necessarily indicate their affinity for a healthy lifestyle or not. If you are overweight, understand that you may have certain genetic disadvantages that you have to work a bit harder at some things than others. Having said that, everyone will have advantages and disadvantages, I try and encourage clients of mine to not allow the disadvantages define who they are or cause them to simply give up hope.