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Gene in Focus - Part 3: ACTN3

Posted 684 Days Ago in: Training, Genetics


The next gene we are going to discuss in the focus series is ACTN3. It’s one of the most well studied genes with regards to sporting performance. ACTN3 codes for a protein that is found exclusively in the fastest kind of muscle fibres, type IIx, called a-actinin-3. Fast twitch muscle fibers can contract quickly and powerfully, and as such are linked to sprinting or weightlifting. Generally, people who are quick or strong will have plenty of type-IIx muscle fibers, whilst people who are better at long distance running will have more type-I muscle fibers (often called slow twitch muscle fibers).

There are two different alleles for ACTN3; C & T. The C allele allows for correct production of the a-actinin-3 protein, and the T version prevents this protein from being made. Not being able to produce this protein does not cause any disease, as muscles can function without it, but it might limit the amount of fast twitch muscle fibre that can be produced. These two different alleles can create three different genotypes; CC, CT and TT. The effects of each of these genotypes are summarized in the table below:




Able to produce a-actinen 3?

Associated performance

Typical Training Response



Strength/ speed/ power combination

Good results from high intensity work



Expected to be good at strength/ speed/ power, less so than CC

Good results from high intensity work



Found more frequently in endurance athletes

Good results from lower intensity work



It isn’t rare to have the TT genotype; roughly 18% of European Caucasians are TT, whilst up to 30% of Asians can have the TT genotype. In people of African decent, the T allele is rarer, and some research has reported that as little as 1% of certain African populations have the TT genotype.


The first studies on ACTN3 were association studies. In these studies, scientists tested a group of people who were not involved in high-level sport, and used them as a control group. They then tested elite sprinters, power athletes, and elite endurance athletes, to see if there were any differences between them. They found that elite speed and power athletes were much more likely to have the C allele in the form of either the CC or CT genotype than the control group. Generally, elite speed power athletes don’t have the TT genotype, as it occurs roughly 3% of these individuals, compared to about 18% of control groups. In fact, in one study no sprint Olympians had the TT genotype. In contrast to this, the studies found that elite endurance athletes were much more likely to have the TT genotype than the control groups.


So what does this mean for you? Your ACTN3 genotype can’t tell you whether you can be a world class sprinter or not, because there are cases of elite power athletes with the TT genotype. However, it can be used to indicate how you will respond to different training. What we know is that individuals with a C allele generally respond better to power training than individuals with the TT genotype. The reason for this is that the C allele allows you to grow type IIx muscle fibers from exercise. These muscles fibers respond really well to power and strength training, and tend to grow larger than other types of muscle. Another interesting study has shown people with the CC genotype have higher levels of testosterone than the TT genotype, with CT falling somewhere in the middle. Testosterone is an additional factor that determines how well someone can gain muscle, with more testosterone allowing more muscle mass to be built. This is part of the reason why men tend to grow muscle tissue more quickly than women, as men have much higher levels of testosterone than females.


In terms of training, research shows that those with a C allele generally see greater improvements in muscle strength and power following high intensity training, such as lifting heavy weights for a low number of repetitions. Having a TT genotype does not mean that you can’t get strong or grow your muscles, it means you just have to train in a way that suits your genetic profile a bit more. This will include doing weights for 12-15 repetitions, trying to take the muscle as close to failure as possible. Conversely, if you have the CC genotype, you should focus a bit more on lifting heavy weights for a lower number of repetitions, somewhere between 3 and 6. If you have the CT genotype, then a mix of both types of training should prove useful.


ACTN3 Gene in Focus DNAFit Genetics Training Power Endurance Workout Gym Fitness


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