On Your Mark Nutrition


If You Have the Gene for Speed, Can You Succeed as an Endurance Athlete?


If your genes say you are a sprinter, what does that mean? What if you train and compete as an endurance athlete?

A few weeks ago I visited Nova Southeastern University to participate in a study, led by Dr. Jose Antonio, testing athletes for the gene for speed (ACTN3 gene). Some of my saliva was collected in a tube, and it was sent off to a lab.

The Verdict:

“You are an RR...homozygous for the speed gene!  You got a full complement of the ACTN3 gene.”

I was pretty excited in my initial reaction. But after a few minutes, I was actually disappointed because my passion is long-distance road cycling. I can ride hard and long. But honestly, I always thought I was a better sprinter off the bike than on the bike. When running, I’m very good at sprinting, but I can’t run long-distance (maybe it’s mental). In cycling, I fatigue quickly while sprinting, but I can easily ride 100+ miles. I’ve even completed a sub-five-hour century ride.

So does ACTN3 define an athlete? Does it predict an athlete’s success?

My Athletic History

I competed in tennis for over 10 years. I was also a volleyball player for 8 years. When we ran suicides in practice, I’d crush them. During freshman year of high school, I was on the track team. I was told I didn’t need to go to practice, and I could just run the 100-meter dash at track meets.

While living in Boston the past two years, I did a lot of boxing, resistance exercise and high intensity interval (HIIT) training at EverybodyFights.

I picked up road cycling two years ago, but I started to take it more seriously over the past year. I was even flying a lot from Boston to Miami last year just to ride my bike.

There are many reasons why I picked up cycling, but for the purpose of this blog, my main reason was because I wanted to be an endurance/ultra-endurance athlete.

Some cyclists do long-distance cycling so they can eat a lot after! But to me, long-distance cycling (especially 100 miles) is an incredible achievement (that not many people attempt) of how much you can push your body and what your body can do. That’s why I do it. There aren’t many 100-mile bike races, especially in South Florida, so I participate in 100-mile charity rides and race them against myself.

My other goal was to compete in USA Cycling, which I’ve recently begun, but most of the races near me are criteriums (a multi-lap race with a high average speed and intensity compared to long-distance cycling races). I don’t compete in them because I never thought speed was my strength….

Essentially, I trained for 10+ years as a sprint/power athlete and two years as an endurance athlete (while doing cross-training that focuses on sprint/power through boxing, resistance exercise and HIIT).

I’m sure there are many athletes with a similar history and training focus as me. So when you get “evidence-based” science like this about yourself, what does it mean? How should you take advantage of it? For me, should I stop cycling and go back to playing tennis or become a sprinter? Should I change my training?

Let’s first talk about the ACTN3 gene.

What is the ACTN3 Gene?

The ACTN3 gene is specifically found in fast-twitch (type II) muscle fibers, which are in charge of producing forceful muscle contraction that are especially needed for sprinting and weight-lifting. The gene produces a protein that regulates the function of these fibers. (Important Note: not having the ACTN3 gene does not necessarily mean that you have a better endurance capacity.)

Genetics strongly influences the ability of type II muscle fibers to generate force at high velocity, speed and tempo of movement and the ability for someone to adapt to exercise training. Over 70 genes have been associated with fitness and performance, but ACTN3 is the first skeletal-muscle gene in which an association has been shown. It has shown a highly significant association with athletic performance and suggests that we have a genetic predisposition toward a particular type of performance: sprint/power or endurance.

The ACTN3 gene is considered to be a potentially useful predictor for athletic performance at the elite level.

Everyone has the ACTN3 gene, but there are three versions.

R: “normal” version

X: “defective” version

RR: homozygous for the gene (i.e., have the complete gene)

RX: heterozygous for the gene (i.e., carrier of the gene)

XX: no gene (i.e., completely deficient) 

According to Dr. Jose Antonio, RR homozygous is common in speed athletes, but many speed athletes are RR or RX (heterozygous, which means you’re a carrier because you have a functional copy of the gene). Being a carrier is helpful. All world-class sprinters either have the complete gene or carry the gene.

ACTN3 Gene Associated with Elite Athletic Performance

A study partnered with the Australian Institute of Sport to investigate ACTN3 genotype frequencies in elite athletes. The definition of “elite” was an athlete who represented Australia in their sport at the international level (some of the participants even competed in the Olympics).

Because ACTN3 is found in fast-twitch muscle fibers, the study hypothesized that a deficiency of ACTN3 would reduce an athlete’s performance in sprint/power events. Therefore, a deficiency in elite sprint athletes would be less likely.

Genotype testing was done using three groups:

Group 1: Sprint/Power Athletes

  • 107 elite athletes (72 male and 35 female)

  • Athletes were: runners in track events < 800 m, swimmers competing in events <200 m, judo athletes, short-distance track cyclists and speed skaters

Group 2: Endurance Athletes

  • 194 athletes (122 male and 72 female)

  • Athletes were: long-distance cyclists, rowers, swimmers competing in distances >400 m, runners competing in track events >5,000 m and cross-country skiers

Group 3: Controls

  • 436 unrelated controls

  • Participants included blood donors, healthy children in an unrelated study and 215 healthy adults

Below is the genotype data:

Source : Yang N, MacArthur DG, Gulbin JP, Hahn G, Beggs AH, Easteal S, et al. ACTN3 genotype is associated with human elite athletic performance.  Am J Hum Genet . 2003;73:627–31.

Source: Yang N, MacArthur DG, Gulbin JP, Hahn G, Beggs AH, Easteal S, et al. ACTN3 genotype is associated with human elite athletic performance. Am J Hum Genet. 2003;73:627–31.


Summary of Results:

  • There were significant allele frequency differences found between sprint athletes and controls for males and females

  • Among sprint athletes, there was a lower frequency of deficiency

  • No female elite sprint athletes or sprint Olympians had an deficiency (, XX)

  • Sprint athletes had a higher frequency of the RR genotype (i.e., complete gene) and a lower frequency of the heterozygous RX genotype (i.e., carrier)

Essentially, the ACTN3 577R allele provides an advantage for power and sprint events. This is still important for those who don’t have the complete gene (RR), but are just a carrier (RX). Carriers have at least one copy of the R allele of ACTN3. This means there is a presence of ACTN3 in your skeletal muscle. All male Olympian power athletes had at least one copy of the R allele of ACTN3.

How Do I Make Sense of What My Genes Tell Me I Am

Obviously, there is evidence that athletic performance is strongly influenced by genetics, but it doesn’t necessarily predict success. Genetics is a piece of the puzzle that is influenced by so many factors. Athletic performance has to be viewed holistically.

Even though it is claimed that the ACTN3 gene may tell you what type of athlete you were born to be, I don’t think so. Just because I have the gene for speed doesn’t mean I’m an elite sprinter. It just means that I have a favorable genetic profile because I have the “tools” in my muscle to perform well in sprint/power events. I still have to train hard and in an optimal training environment to take advantage of that gene and earn athletic success.

How This Knowledge Changes My Perspective as an Athlete:

  • I have the muscle strength and sprint ability that can help me in sprint/power events.

  • I may just need to work harder as an endurance athlete.

  • To take advantage of this in cycling, I should maybe race in time trial and criteriums, and I should pace myself more in long-distance cycling and sprint near the finish.

  • When I do sprint in training, I know I can go a lot harder/faster than I may have originally been allowing myself.


  • Those with an deficiency have a lower muscle strength and weaker sprint ability than those who either have the complete gene or at least one copy of the gene.

  • At the Olympic-level, having the gene makes a big difference.

  • Sports that are more skills focused are not influenced by ACTN3.

  • ACTN3 is just one factor in the big picture of whether or not you excel in a sport. There are many other genetic (e.g., traits for muscle strength and cardiorespiratory performance), psychological (the main reason why I failed at tennis) and environmental factors, which ACTN3 does not influence, that play a role in performance (e.g., nutrition, dedication, mentality, coaches, etc.).

  • Optimal nutritional practices for health and performance are more powerful than having the gene for speed. Nutrition can trump this genetic ability!

Ultimately, the ACTN3 gene doesn’t define or predict the success of an athlete who’s not at the Olympic level. It’s just cool information to know that may influence how you approach your sport.

I may be lugging around the ACTN3 gene, but you won’t see me in the 100-meter dash at the 2020 Olympics. You may catch me competing in more time trials and sprinting a 100-mile bike race!

Katie Mark