Knowing your personal muscle fiber make-up can be an invaluable aid when it comes to properly targeting your training program. If you're working your muscles in the wrong way, you'll be cheating yourself out of hard-earned results.
Every muscle in your body is made up of a bundle of small fibers. In each bundle, you have two main types of fibers: slow twitch and fast twitch. I will explain exactly what these are in a moment. The percentages of these different fiber types that your muscles are made of can help you determine exactly how you should train each particular muscle group in your body.
Slow Twitch: These are also known as Type I or red muscle fibers. They are responsible for long-duration, low intensity activity such as walking or any other aerobic activity.
Fast Twitch: These are known as Type 2 or white muscle fibers (divided further into A and B). They are responsible for short-duration, high intensity activity. Type 2B fibers are built for explosive, very short-duration activity such as Olympic lifts. Type 2A fibers are designed for short-to-moderate duration, moderate-to-high intensity work, as is seen in most weight training activities.
By looking at elite athletes in different sports, you can see extreme examples of each make-up of muscle fiber. At the slow twitch end is the endurance athlete, such as the marathon runner. These athletes can have up to 80% or more of slow twitch muscle fibers in their bodies, making them extremely efficient over long distances.
At the fast twitch end is the sprinter. World-class sprinters can have up to 80% or more of fast twitch muscle fibers in their body, making them extremely fast, strong and powerful but with limited endurance.
