Running and Genetics

Running fast is very much dependent on your body structure.  People have two different types of muscle fiber, for the most part: fast-twitch fibers, and slow-twitch fibers. Fast-twitch muscles make sprinters because they can contract much faster, propelling a person to faster short-distance speeds than a marathon runner, who has slow-twitch muscles.  You lose speed, but you gain endurance.

What type you have is determined mostly by genetics.  You can alter them to a degree by exercising in a particular way, but if you are born with predominantly fast-twitch muscles, you will likely never be a marathoner. However, that doesn’t you can learn how to run faster or even finish 1st in an upcoming race.