Now that you have read about the different muscle fibers, it should be clear why skeletal muscles that have predominantly slow-twitch muscle fibers are red in color (more blood flow) while skeletal muscles that have predominantly fast-twitch muscles fibers are white in color (less blood flow). The percentage of your muscles that are fast twitch or slow twitch makes a big difference in your ability to perform in sports. Remember that everyone has a blend of fast-twitch and slow-twitch fibers. For most people this blend is equal (50% fast twitch and 50% slow twitch) however, there is a great disparity when it comes to elite athletes. For example, Olympic marathon runners have as much as 80% slow-twitch fibers in their leg muscles, while Olympic sprinters have as much as 70% fast-twitch fibers in their leg muscles. If you consider the characteristics of these fibers, this fiber-type distribution makes sense. Consider the fiber-type distributions among rowers, wide receivers in football, cross-country skiers, and hockey players.
