photo by cas; Soccer players like the ones shown in this picture probably excel at the sport because they have an a-actinin-3 deficiency, which allows them to use their energy more efficiently.
Soccer practice was brutal. The hot summer heat made every drill twice as hard as usual. Everybody was a little bit off of their game, however I was particularly sluggish. The coaches called for a water break after finally noticing that our dehydration was significantly affecting our performance. I was dragging my feet on the way to the water cooler when one of my coaches, Brett, pulled me aside from the rest of the players.
“What’s wrong Alec?” Brett asked, “You look really off today.” “Yeah,” I replied, “this heat is killing me, plus, I’m not a soccer player.” It was true, I was a basketball player, and soccer was just not my sport. I am fast at times, but I get winded just minutes after a soccer game starts. I only joined the team because Coach Brett begged me. We were short of the minimum amount of players required and I was the only boy left in camp between the ages of thirteen and fifteen with some athletic ability who was available.
“It doesn’t matter if you’re a soccer player,” Coach Brett said, “If you put forth your very best effort, you will ALWAYS be the most fit and best soccer player on the field.” Well, not exactly. After further research, I found out that Coach Brett was wrong, athletic ability was not one hundred percent earned with hard work. Rather, genetics play an essential role in modern human athletic ability as well as hard work. To be more specific, the ACTN3 gene and its variation in populations throughout the world provide information about a fascinating link between the survival of ancient humans and the athletic ability of modern man.
The human ACTN3 gene encodes a protein known as a-actinin-3 , which helps the support system in fast-twitching skeletal muscle fibers. In 1999, scientists revealed that the a-actinin-3 protein was absent in more than one billion people worldwide. These one billion people with an a-actinin-3 deficiency were able to compensate by producing a similar protein known as a-actinin-2. There is an evolutionary “trade off” by possessing or not possessing the ACTN3 gene.
To acquire information and research about this evolutionary “trade off”, I contacted Dr. Kathryn North, who currently works for the Institute for Neuromuscular Research and asked her if she could help me. Dr. North was very generous and sent me documents of studies that she was involved in. In one of the studies, genetically engineered mice were used to simulate the effect of ACTN3 deficiency in humans. Observations that were obtained from this study include information about a-actinin-3’s role in the regulation of skeletal muscle’s metabolism as well as it’s mass and fiber size. Dr. North and the rest of the scientists who conducted this study also discovered something remarkable. The mice that were lacking the a-actinin-3 protein used their energy more efficiently because the muscle fibers of those mice had the metabolic and contractile properties of slow oxidative fibers. Therefore, the mice with an a-actinin-3 deficiency were able to outlast the other mice that “possessed” the a-actinin-3 in endurance activities. From this experiment, these scientists concluded that having an a-actinin-3 deficiency is associated with a more efficient aerobic muscle metabolism, which strongly favors endurance activities such as running a marathon or long distance swimming races.
However, those mice that possessed the a-actinin-3 protein had a different advantage that might be more effective in a different environment. A-actinin-3 is specifically found in fast-twitch myofibers that are responsible for generating forces at a high velocity. Since these mice possessed the a-actinin-3 protein, they were able to generate the rapid contractions needed to excel in sprinting. It all depends on which environment you are in that determines whether having or not having the a-actinin-3 protein works to your advantage.
Photo by Thomas Hawk; People who excel at short distance sprint sports like basketball probably possess the a-actinin-3 protein because the a-actinin-3 protein allows your fast twitch skeletal muscle fibers to generate more force.
Given this information, I hypothesize that I am a person who has the ACTN3 gene. A person like Coach Brett on the other hand probably possesses the a-actinin-2 protein because of his inability to excel in short distance sprinting activities and excel in long distance endurance activities. So yes, Coach Brett, you can work hard to become the best athlete you can be in a particular sport. However, the types of sports that you excel at are indeed genetically influenced. So I may not be a soccer player Coach Brett, but no matter how hard you try, you’re never going to beat me at basketball, that’s MY sport.
How do you expect the population of people who possess the a-actinin-3 to change in the future based on the current state of man? Why do you think humans first developed an a-actinin-3 deficiency? Do you think evolution and natural selection played a role, why or why not? Provide evidence based on the time period when some humans first developed an a-actinin-3 deficiency (300 million years ago).
