Muscle Fiber Types and Their Adaptations Through Training

Posted by Shelley Harper on Jun 30, 2014 8:32:00 AM

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muscle fiber types

Building muscle is essential to all sports. From gymnastics to swimming to basketball, developing muscle will improve strength, stamina and performance. However, compare Nastia Liukin to Michael Phelps to Lebron James and you find that their muscle compositions are very different. Each of these Olympians has found a way to build not just muscle, but also the right muscle on their journey to Gold. When looking to increase muscle mass it is important to make sure you are training the correct type of muscle fiber specific to your sport and event. You wouldn’t see Michael Phelps and Lebron James doing the same strength routine nor will you see a 50 Freestyle specialist do the same routine as a distance swimmer. Specificity is key in strength training and vital for success.


Muscle Fiber Types:

muscle fibers


The chart above shows the differences among the three main muscle fiber types: Slow Oxidative, Fast Oxidative/Glycolytic and Fast Glycolytic. As you can see slow oxidative fibers are not as strong as the other two, but can be repeatedly used for extended periods of time without fatiguing--essential for the endurance athlete. Fast oxidative/glycolytic fibers provide a faster twitch and larger force while still maintaining resistance to fatigue--great for extended sprinters such as a 400meter run specialist. Lastly, fast glycolytic fibers provided the largest force and fastest twitch speed but are highly fatigue-able and are reserved for high-intensity bursts such as a short sprint or maximal lifts.


Muscle Fiber types in Elite Athletes


Athletes at the top of their sports have shown important specialized muscle fiber type characteristics. For example, sprint runners have predominately Type IIB fast glycolytic muscle fibers, while distance runners have a larger proportion of slow-twitch, high oxidative muscle fibers. Training and building the right muscle fibers is key to athletic success.


Training your Muscle Fibers


Myoplasticity refers to the capacity of skeletal muscles to change. Training can increase muscle mass and alter muscle fiber composition depending on the specifics of an athlete’s training. Let’s look at how endurance and strength training each change muscles in different ways.


  • Endurance training is when an athlete’s muscles are performing high-frequency, low-force output activity. In other words, the muscles are being repeatedly activated for long periods of time at a lesser power. While endurance training does not significantly increase your muscle fiber cross sectional area, there are many other significant adaptations that improve performance. Most significantly is the increase in mitochrondrial mass allowing for an increase in oxidative metabolism in skeletal muscle.
  • Strength training is when your muscles are performing low-frequency, high-force output activity. Strength training induces hypertrophy, which is the increase of the cross sectional area of a muscle fiber. Strength training results in the hypertrophy of both type I and type II muscle fibers. It is also important to note that mitochondrial density actually decreases with an exclusive high-intensity strength program. This is important because athletes who only train with resistance are more likely to find a decrease in muscle endurance capacity. Refer back to Megan’s January post on finding your speed and power for more detail on resistance training.


The Take-Away: 5 things to remember


  1. There are three different muscle fiber types: slow oxidative, fast oxidative/glycol tic and fast glycolytic.
  2. Endurance training has minimal effects on the size of muscle, however it does increase mitochrondrial mass allowing for increased oxidative metabolism in skeletal muscle.
  3. Strength training induces hypertrophy (increase of muscle fiber size) of both type I and type II fibers, however it results in decreased mitochrondrial mass of skeletal muscle.
  4. Combining endurance training with strength training is key to maximizing your muscles power and resistance to fatigue.
  5. Lastly, specificity in training is KEY. Exclusively endurance training for a sprint event will not provide you will the correct muscle adaptations, just as entirely sprint training will not prepare you for an endurance event.


  • Brooks, George et al. Exercise Physiology: Human Bioenergetics and Its Applications. McGraw Hill: New York. 2005.


Topics: S+C