Fiber type, limb lengths, nervous system function, hormone levels, receptor sensitivity, they have identified certain genetic markers associated with things like power production and endurance and there tends to be genetic trends towards either strength/power production or endurance performance that show up pretty reliably.
None of which is going to be modifiable with any current training or dietary paradigm. At best you can maximize your genetic potential by doing things right. At worst you never get clos to your genetic potential by doing them wrong.
None of which discounts the importance of hard/smart/consistent work or anything else. But at the topmost level, everybody works hard. And small differences in genetically unmodifiable factors are going to become magnified. It may not make a shit’s worth of difference at lower levels but at the top level, small percentage differences between individuals can mean the difference between first and last place.
Here’s a recent review relevant to speed for example. And one of a more general bent.
Physiology (Bethesda). 2010 Aug;25(4):250-9.
A gene for speed: the emerging role of alpha-actinin-3 in muscle metabolism.
Berman Y, North KN.
Institute for Neuroscience and Muscle Research, The Children’s Hospital at Westmead, Westmead, Australia.
A common polymorphism (R577X) in the ACTN3 gene results in complete deficiency of alpha-actinin-3 protein in approximately 16% of humans worldwide. The presence of alpha-actinin-3 protein is associated with improved sprint/power performance in athletes and the general population. Despite this, there is evidence that the null genotype XX has been acted on by recent positive selection, likely due to its emerging role in the regulation of muscle metabolism. alpha-Actinin-3 deficiency reduces the activity of glycogen phosphorylase and results in a fundamental shift toward more oxidative pathways of energy utilization.
Med Sport Sci. 2009;54:43-71. Epub 2009 Aug 17.
Genes, athlete status and training – An overview.
Ahmetov II, Rogozkin VA.
Sports Genetics Laboratory, St Petersburg Research Institute of Physical Culture, St. Petersburg, Russia. firstname.lastname@example.org
Significant data confirming the influence of genes on human physical performance and elite athlete status have been accumulated in recent years. Research of gene variants that may explain differences in physical capabilities and training-induced effects between subjects is widely carried out. In this review, the findings of genetic studies investigating DNA polymorphisms and their association with elite athlete status and training responses are reported. A literature search revealed that at least 36 genetic markers (located within 20 autosomal genes, mitochondrial DNA and Y-chromosome) are linked to elite athlete status and 39 genetic markers (located within 19 genes and mitochondrial DNA) may explain, in part, an interindividual variability of physical performance characteristics in response to endurance/strength training. Although more replication studies are needed, the preliminary data suggest an opportunity to use some of these genetic markers in an individually tailored prescription of lifestyle/exercise for health and sports performance.