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What do your genes know about your physical abilities, and should you be listening to them?

In 1994, an athlete from California redefined our expectations of what our bodies are capable of achieving. At the age of 40, Dave Scott completed an Ironman triathlon race in under eight and a half hours. Arguably the most grueling test for physical fitness, the Ironman race consists of a 2.4-mile swim, a 112-mile bicycle ride, and a marathon 26.22-mile run. Dave’s finish time resulted in a second place finish in a race that many trained endurance athletes fail to complete. Can genetics explain the underlying forces that help athletes like Dave, while holding back others? Modern advances in human genomics may hold the key to this answer.

Can you go longer, faster, and stronger?

Research has shown us that our physical fitness can be the product of multiple factors such as training, diet, geographical location and genetics. But to what extent do our genes dictate our athletic potential? One of the earliest known accounts of this question dates as far back as over 2000 years ago. In his book “Dietetics” (400 BC), Hippocrates proposes that predisposition, now known as genetics, can have a positive effect on our physical fitness. Modern discoveries in the field of Sports Genetics have at least partially validated Hippocrates’ postulation. Approximately 300 genetic variations known as DNA polymorphisms have been demonstrated to associate with human physical performance. For example, maximal oxygen uptake (VO2max) is linked to aerobic endurance and it has been shown to improve through exercise significantly at a higher rate in individuals that possess specific variations in genes associated with oxygen delivery such as the catalase (CAT) gene. On the other hand, variations in another oxygen delivery gene, the nitric oxide synthase 3 (NOS3), have been shown to significantly reduce response to training. In addition to the genes related to oxygen delivery, it has been suggested that genes associated with electrolyte balance and energy production may also influence the improvement of VO2max in response to athletic training programs. Therefore, these genes appear to be part of the reason why, given the same training program, some people respond very well to targeted training, while others only have a mild or slow increase in their cardiorespiratory capability. One strong piece of evidence that links genetics to VO2max improvement, came from a large genetics study known as HERITAGE. This research program entailed studying 99 families who completed 20 weeks of moderate intensity training. The interesting results of this research suggested that approximately 50% of the response to training was caused by the genetic makeup of the family members because the variation between different families was significantly higher than variation within members of the same family.

Want to excel at playing football?

Physical fitness is not limited to endurance capability. What if, like a football player, you have an inclination towards generating short bursts of power such as sprints or weightlifting? This is perhaps also due to our genetic predisposition. There may even have been an evolutionary “trade-off” between human speed and endurance capabilities. A research team led by Professor Kathryn North, at the University of Sydney in Australia has shown that a specific protein can help our muscles contract at high speeds, in turn directly affecting our sprint speed. This protein is found in relatively higher amounts in our muscle cells and is coded by a gene named ACTN3. Interestingly the same research group showed that both male and female athletes who excel at sprinting are more likely to have the same genetic variation in the ACTN3 gene. 

How to be at the top of your game

Unfortunately, it is still impossible to know exactly how much the known genetic variations can influence sporting performance in individuals. That is because the human genome is extremely complex, and the products of multiple genes can interact with each other to produce entirely different outcomes. This gap in our knowledge has made it difficult to apply our theoretical knowledge about genes to real life performance improvements. Therefore, sports-medicine scientists cannot reliably predict sports performance based on our current knowledge of the 200 or so genes linked to athletic performance. For example, genetic variations shown to influence athletic performance in one group of athletes have not been a reliable predictor in future studies involving different groups of athletes.

The good news is that we now have sufficient scientific evidence that our genes have the potential to help or hinder specific athletic abilities. These small-scale genetic studies on a limited number of elite athletes have now encouraged large international collaborations such as the Athlome Project Consortium, which is a concerted effort to use whole genome data, metabolic profiling, and other large-scale biological studies to identify the markers of athletic performance. Future research, in large numbers of athletes, will help us gain a better understanding of genetic variants (mutations and DNA polymorphisms) that influence the heritability of athlete ability.

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