«Your genes reflect your potential, not your destiny»- Bruce Lipton

Genes determine almost nothing, but they condition almost everything. Your capabilities and observable traits are influenced by the genetic heritage of your ancestors, from your intelligence to your political leanings (article, study).

Long ago we saw that knowing our genome can help us personalize our diet (Article). Today we will carry out the same analysis in the sports field. Using my own genes as an example, we will explore the impact of our genetic code on performance, but also injury risk and supplementation strategies.

Strength or Resistance Profile

Multiple aspects influence your predisposition to perform better in short explosive events or in long aerobic activities such as a marathon.

In this sense, the famous ACTN3 gene, which expresses its protein in fast muscle fibers (or type II), increasing its force transmission capacity (meta-analysis, study, study, study). Depending on your specific polymorphism, you may have inherited two active copies (one from your father and one from your mother), one active and one inactive, or have both silenced.

In my case, I have both active copies

The vast majority of great explosive athletes, from weightlifters to sprinters, have the active version, giving it the colloquial name of the speed gene.

The inactive version (silenced copies of the father and mother), on the contrary, favors performance in resistance tests, and it seems that this variant evolved especially in areas with less food (study), where energy efficiency was more relevant to cover greater distances Looking for food.

Of course it takes a lot more to be a speed champion than a good version of this gen. Many other genes and factors influence your strength / endurance profile (study, study, study), placing you somewhere in a spread spectrum.

In my case, I have for example the “explosive” version of the ACTN3 gene, being closer to the extreme of Strength / Power. It is no surprise. I always had a good vertical jump and was good at speed, while hating long distance.

Many other anatomical factors also influence (also partly heritable), such as symmetrical knees and ankles (study, study) or percentage of muscle fibers that you have of each type, which we explore below.

Can the% of muscle fibers be altered?

Simplifying, there are two types of muscle fibers:

  • Slow fibers (type I or red): Their favorite fuel is fatty acids, which are easily oxidized thanks to their high mitochondrial density. They are very resistant to fatigue but take their time to produce energy, hence they have little explosive capacity.
  • Fast fibers (type II or white): They mainly use glycogen and phosphocreatine, fuels that are not energy efficient but capable of producing force quickly. The price of this explosiveness is that they tire easily.

We have a combination of slow and fast fibers in all muscles, but there is great individual variability. Marathoners have many more slow fibers than sprinters.

The percentage of fast and slow fibers varies significantly in the different sports disciplines

Although the genetic factor is the most important (detail), the type of training you do partly conditions the resulting fiber distribution (study, study). Long-term aerobic training favors slow fibers, and strength training for fast ones. If you want the body of a sprinter, you must train like a sprinter.

The athlete on the left only runs long distance. The one on the right does heptathlon: 200 and 800 m sprints and 100 m hurdles, high and long jump, shot put and javelin.

Gain muscle mass

Fast fibers have a greater potential for hypertrophy, but muscle gain depends on many other genetic factors, related for example to the activation capacity of satellite cells.

In my case, the muscle gain potential is moderate, and it also fits with my experience. Only when I started to program well and prioritize the right exercises did I have good results.


Dozens of genes are known to influence the risk of different injuries (study, study), highlighting those related to the production of collagen, the main protein in bones and connective tissue.

For example, the gene COL1A1 It is one of those responsible for the synthesis and structure of collagen, and the TT combination (a T allele inherited from the father and another from the mother) is associated with a lower risk of anterior cruciate ligament injuries (study, study).

Luckily, I have this combination, and maybe that’s partly why I’ve never suffered this injury. Knock on wood. This variant also appears to protect against Achilles tendon tears and dislocations (study).

Another interesting gene is Col5A1 (study, study), where the CC combination is associated with better flexibility and lower risk of tendon injury (study, study, study). In this case I have not been so lucky (I am CT), and indeed flexibility has never been my specialty.

Increased risk of injury in CT variant. Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4523805/

Although to a lesser extent, another protein is also relevant: elastin, which gives elasticity to tough collagen fibers. Elastic ligaments are more resilient than rigid ones, reducing the risk of injury. The AA version is associated with a higher risk of injury and the GG with less. Mine is AG, conferring a medium risk (study).

Although muscle injuries are usually less serious than joint injuries, there are also multiple variants associated with different risks (study, study, study), such as these two:

  • IGF2: Growth factor that promotes cell proliferation.
  • CCL2: Regulates inflammation and muscle regeneration processes.


I have discussed the most effective supplements, such as creatine and caffeine, multiple times. But again your genes influence its effect (detail).

People with fewer fast fibers will experience less benefit from creatine at the muscle level (study), and this depends in part on the active version of the sprinter gene (ACTN3).

For its part, the gene CYP1A2 determines the ability to metabolize caffeine, and rapid metabolizers (AA genotype) obtain benefits not available to the rest (study).

In my case, I respond well to both, and that’s why I like them so much.

If you are a slow metabolizer of caffeine, it is advisable to limit it.

Do genetic tests help us personalize training?

This is the one million question. It is one thing to find correlations between genes and different aspects of performance, and quite another to be able to take advantage of that information to effectively perform better. In this area, the evidence is still very scarce.

A good example of the future potential of this technology is a recent study, which used fifteen genes to determine the profile of each athlete (strength / power or endurance), then evaluating their response to two training approaches: high intensity and low intensity.

Both groups (genetic strength / power and endurance profile) completed the workouts sequentially, ultimately evaluating improvements in various performance metrics.

The bottom line is that the groups improved the most when they were assigned to training that matched their original genetics.

Although it is an interesting and well-controlled study (it used randomization and double blindness), its practical application is limited. In addition, they did not evaluate gains in strength or muscle mass, a relevant aspect for many.

Is it worth investing in a sports genetic test?

In most cases, I think not.

If you have been training for a long time, surely a genetic test will only confirm your intuitions. Even if you get a surprise, it is difficult for it to provide you with something practical:

  • Even if you have an endurance profile, you will benefit from training strength and power.
  • Even if your risk of injury is lower, you should continue to improve your mobility and pay attention to technique.
  • Whatever your muscular potential, you must apply the same rules to develop it.
  • Even if you don’t respond to creatine muscularly, it can benefit you in other ways.

What’s more, for each supposed genetic rule, you will always find an exception. Do you remember the famous gene for explosiveness? Well, a Spanish athlete jumped 8.23m without him (detail).

Genes are very relevant, but we are far from unraveling their mysteries. We ignore many complex relationships, both between genes themselves and between them and the environment in which they develop. Today, we know much better the impact of our actions, and we must focus our efforts on making better decisions.

Note: If you still want to explore your DNA, there are multiple options. I did the initial test with 23andMe, and then I used the DNAactive sports analysis.