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Are Athletes Born or Made?
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by Carol Torgan, Ph.D.

Ever dream of standing atop a podium and having a medal placed around your neck? Ever wonder what your optimal athletic potential is? As we marvel at the athletic feats on display at the winter Olympics this month, it?s the perfect time to explore the nature vs. nurture debate. How much is athletic prowess due to genetics and how much is it due to training and environment?

A Family Affair

If a room full of PPTC members undertook an identical exercise training program, some would experience large improvements in endurance and others would hardly improve at all. How much of this variability in training response is due to genetics? Scientists have been asking this question for decades. One way of exploring the link between heredity and performance is to study families. Comparisons of fitness components and trainability can be made between identical twins (from one egg) and fraternal twins (from different eggs). Identical twins share the same genes, whereas fraternal twins share only one-half of their genes. If identical twins are more similar in a certain capacity than fraternal twins, a genetic component is thought to be involved. Differences between identical twins presumably stem from environmental factors.

The findings from twin and other familial studies reveal that numerous performance characteristics are influenced by genetics. The genetic component is about 40-50% for the proportion of slow-twitch (vs. fast-twitch) muscle fibers in humans, 30-70% for heart size and cardiac functions, and around 25-40% for maximal oxygen consumption. Other characteristics that appear to have a sizable genetic component include metabolic rate, blood volume, flexibility, anaerobic performance and body fat distribution.

Lean and Mean Genes

A characteristic such as muscle fiber type represents a composite of numerous proteins that are the products of genes. Genes are the basic physical and functional units of heredity. Each gene is a specific sequence of DNA that encodes the blue print to make a protein. The working draft of the human genome completed last year reveals that each of us has approximately 35,000 genes. This is only about one third of what was expected, and only about twice as many as a commonly studied little worm.

Scientists are studying sequence variants in genes, which are akin to misspelled words. These misspellings, or polymorphisms, may underlie a person?s predisposition to a disease or influence how they will respond to certain drugs. Thus mapping them in individuals and families is one key to the future of personalized medicine.

Polymorphisms also seem to partially explain why there are differences in how people respond to exercise training. Misspellings in certain genes, such as those related to energy metabolism, appear to affect physical performance. Researchers are now trying to identify and map all the polymorphisms and genes related to physical achievement. Last year exercise science experts from around the world constructed an initial draft of a Human Gene Map for Performance and Health-Related Fitness.

The Combination Platter

Before you start cursing your parents, stop and consider all the factors that are necessary to be a successful athlete. In addition to physical capabilities, athletic performance requires mental characteristics that include motivation, desire, concentration, competitiveness, learning ability and, at times, pain threshold. Environmental factors such as coaching, training facilities, equipment, nutrition and family support, are also key.

A cyclist genetically predisposed to outstanding endurance but lacking the desire to train will be less successful than another cyclist who has a merely good endurance capacity but a much greater desire to train. Genetically under-endowed folks still have a chance for success when factors such as coaching and equipment are added to the equation.

Brave New World

The era of the genome has profound implications for the future of athletics. Gene therapy and cell therapy (including stem cell therapy) could be used to help prevent or treat injuries such as bone fractures, meniscal and ligament tears, and muscle contusions, lacerations and strains. Genetic screening to test for diseases and the predisposition to diseases will become routine. It could also be used to help identify prospective athletes and ascertain the sport for which they would best be suited.

Unfortunately, rapidly growing genetic technologies might be abused by those with a desire to win at any cost. It?s possible that drug doping could be replaced by gene doping. On paper, the process is relatively straightforward. In one technique benign viruses engineered to contain a desired gene are injected into the body where the gene is expressed. For example, a virus that contains a gene for erythropoietin (EPO) has been injected into the muscles of animals, resulting in increased hematocrit. While useful in treating disorders such as hemophilia, this procedure could theoretically be utilized as a genetic form of blood doping. Other genes with therapeutic potential that might be exploited to enhance athletic performance include numerous growth hormones that could increase muscle mass. Although routine in many laboratories, these techniques are still highly experimental, and they present many technical and ethical concerns. The temptation for misuse of gene therapy is obvious and the International Olympic Committee is already looking into testing methods to detect genetic abuse.

The bottom line is that athletes are born and made. Those elite few standing on Olympic podiums to receive medals generally have the genetic predispositions, as well as the right personality types and support systems. The upper limits of performance that individuals can achieve are most likely set by inherited traits, but in the future those boundaries could be altered by genetic engineering. Athletes might then be sponsored not only by shoe manufacturers, but also by biotech companies.

Recommended References

http://www.geneforum.org/
This nonpartisan organization promotes discussion and education about genome science.

http://www.nhgri.nih.gov/

The home page of the National Human Genome Research Institute has links to a glossary of genetic terms, the Human Genome Project, and the ELSI (Ethical, Legal and Social Issues) Program, among others.

Carol Torgan is an exercise physiologist and Fellow of the American College of Sports Medicine.

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