Ever wondered if Olympic athletes are trully gifted genetically? Or does all their success come purely from hard work?

Well, some humans are faster and more athletic because they're born with more fast twitch muscle fiber than others. You see, muscles are made of two kinds of fibers--fast twitch and slow twitch. Slow-twitch fibers use energy aerobically and can work for long periods of time before getting tired. They contract more slowly, but can keep going without burning themselves out.

Slow twitch fibers have a lot of myoglobin, a protein that helps transfer oxygen into the mitochondria, the power houses of the cell that produce cellular energy. Marathon runners must have a lot of slow twitch muscle fibers since they have to keep going for long periods. Therefore, sprinters have a lot of fast twitch muscle fiber.

Fast twitch fibers consume energy quickly and are good for short, powerful bursts of movement like sprinting and jumping. World-class sprinters typically have about 80% fast twitch muscle fiber. Of course, they also train incredibly hard to develop their natural gifts. Olympic gold is not won by muscle fiber alone.