One of the most common fitness goals for many is muscle definition. Muscles generally define body structure. However, there is a multitude of factors on how one can achieve a certain look. Among these are the types of muscle fibers which play a huge role in creating those sought-after curves and shapes. These silhouettes are usually achieved by contracting muscle fibers in a certain way, somehow altering and strengthening those through rigorous and consistent workouts.
If you are interested in achieving results, understanding this complex system could help you create appropriate exercise programs based on your goals. Each muscle fiber responds differently. Knowing how to generate those responses would help you improve your overall efficiency when working out.
What is Muscle Fiber?
Muscle fibers, or Myocytes, are the basic building block of a muscle. Each of these fibers contains myofibrils, which are strands containing two types of protein — myosin and actin. The interaction of these strands causes our muscles to contract and, thereafter, leads to muscle protein synthesis.
Generally, these fibers control one’s movements throughout the body. Each type and classification plays a different role to help us function.
What are the types of Muscle Fibers?
Muscle fibers are classified based on speed type, size color, its response rate to stimulus, and other characteristics.
There are two main types of muscle fibers: the slow-twitch (type I) and the fast-twitch (type II),
which are broken down into two (type IIa and type IIb).
In a nutshell, slow-twitch muscle fibers help in long endurance workouts. On the other hand, fast-twitch muscle fibers are used in powerful bursts of movements like sprints.
Type I Muscle Fiber Type (Slow-twitch)
Type I (slow-twitch) fibers have a dark and reddish appearance. These also have a higher density of mitochondria, which are good for aerobic metabolism. These also consist of low glycogen, giving it lower resistance to fatigue and tiredness.
Type I fibers cannot contract muscles easily. They typically require more work to build up, making it ideal for endurance activities. These are also highly oxidative. They efficiently use oxygen to generate more adenosine triphosphate (ATP) for continuous, extended muscle contractions for long periods of time.
These muscle fibers are usually associated with lower-intensity, endurance-oriented activities like walking, running, and cycling.
Type IIA Muscle Fiber Type (Intermediate Fast-twitch)
Usually referred to as the moderate type I and type II, Type IIA finds a balance of adopting characteristics from both types.
Type IIA fibers have high fatigue resistance with high glycogen content, making it easy to perform long anaerobic exercises. Like the Type I fiber, these also have high oxidative enzymes, using up a lot of oxygen to create energy. They can be involved in aerobic activities as these fibers have mitochondria. They can also be used to produce rapid force for activities that require a high amount of strength or power.
Fast-twitch muscle fibers have a bigger diameter compared to Type I. These make it play a more significant role when it comes to muscle growth.
Type IIB Muscle Fiber Type (Fast-twitch)
Known as the anaerobic muscle fibers, Type IIB fibers store energy for a short burst of high-intensive activities. This type of muscle fiber uses anaerobic metabolism to create energy and has the highest rate of contraction.
However, Type IIB fibers have low resistance to fatigue due to its limited supply of stored energy. These are usually associated with strength and power activities like sprints and weightlifting.
Type IIB fibers do not have mitochondria. These do not have any color and usually have white or pale appearance.
How do you identify your muscle fiber type?
While everyone has both types, people usually have a predominant muscle fiber. The best way to determine it is through muscle biopsy. It is where professionals collect muscle samples and test it within a laboratory.
Other methods include personal observation and exercise tests. These would examine one’s endurance and capacity to exert energy in different periods of time.
Can Muscle Fiber Types Change?
Yes, muscle fiber types can change depending on training and circumstances. The most common change is the movement of Type IIA to Type IIB. It is where there is an observable increase in the capillary of fiber ratio after following a high exercise training.
Changes from Type I to Type II are very rare. These occur mostly in the case of drastic changes like injuries. There is also some evidence that shows changes from fast to slow. However, the scientific community continues to research and question this concept.
Does muscle fiber type affect sports performance?
Not entirely but it may influence the sports where you are naturally good at. Most Olympic athletes excel at sports where it matches their genetic makeup. While it may be a part of an athlete’s success, it cannot be a sole predictor of performance.
Does Fiber Type Influence Muscle Growth?
Yes. An old study conducted on mice showed that there is significant muscle increase of Type II muscle fiber, compared to that of Type I.
Type I has low resistance to fatigue, meaning that it is likely to produce less force on the muscle, thus, slowing muscle growth. Type II, on the other hand, has low oxidative enzymes and can easily carry out high-intensity exercises. This type has the most effect on muscle growth.
Many articles about muscle growth would have sidelined on the topic of muscle fiber types. However, most of them only focus on its insignificance to muscle growth. Its effects may not directly reflect muscle growth. Still, it definitely has an important role in determining the right exercises and programs to achieve your best performance. This is not only limited to toning your body. It is also important for other health workers, such as trainers, clinical staff, and physiotherapists, to further assess your performance. This assessment can then help you grow and prevent muscle-related diseases and injuries.
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