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
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
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
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
This nonpartisan organization promotes discussion and education about genome science.
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.