This is a general overview of the type of muscle fibers found in the body and how they may contribute to one’s exercise/sport performance.
Most skeletal muscles (muscles attached to bone by tendons which allow the body to move voluntarily) are comprised of two types of muscle fibers. Those fibers are referred to as slow twitch and fast twitch.
The amount of those particular fibers present in each muscle can vary from muscle to muscle and from person to person.
The percentage of a particular type of fiber your body has, which is thought to be genetically predetermined, may be a factor in what type of physical activity you excel at or tend to gravitate to.
The skinny on the slow twitch:
Known as Type 1 or slow oxidative, these fibers have a high level of aerobic endurance and are slow to fatigue. Because they are permeated with blood (oxidized), they have a red color. Exercises such as long distance running, swimming and cycling are good examples of the body’s use of slow twitch fibers. If you tend to gravitate towards these type of exercises, then you may have a greater percentage of slow twitch fibers present in your body.
The facts on the fast twitch:
These fibers are divided into two types:
1) fast twitch a (Type II A or fast oxidative glycolytic)
2) fast twitch b (Type II B or fast glycolytic)
Both of the fast twitch fiber types have a low level of aerobic endurance, are less permeated with blood and have a pale color.
Type II A fibers fatigue quickly but can use both aerobic and anaerobic systems for short duration, high-intensity exercises. Sprinting is a good example of the body’s use of these fibers. If you tend to gravitate towards this type of exercise, then you may have a greater percentage of fast twitch Type II A fibers present in your body.
Type II B fibers fatigue quickly and are used for short period high-intensity, maximum strength, explosive type exercises. Olympic lifts are a good example of the body’s use of these fibers. If you tend to gravitate towards this type of exercise, then you may have a greater percentage of fast twitch Type II B fibers present in your body.
Fibers are used for exercise according to the size of their motor unit (a bundle or grouping of muscle fibers) with the smaller units being recruited first. Slow twitch fibers have small motor units while fast twitch fibers have large units. The order of which fibers are recruited begin with slow twitch, then fast II A and finally fast II B.
Or think of it this way, the larger amount of force needed for a movement, the larger the employed motor unit will be.
Because there is no hard science behind the muscle fiber theory, there are conflicting opinions on their role.
Some believe that the recruitment of these particular fiber types are inconsequential in relation to the success or gravitation toward an exercise or sport.
One argument being that there are more forces at play, (the role of neurons, mental strength, opportunity, nutrition…and I could go on and on), that contribute to the success or gravitation to a particular type of exercise/sport.
I agree with that assessment but I do not discount the fact that one’s genetic make-up is an important factor in overall success.
Do you have an exercise or sport that you gravitate to? Please share…