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Run, Forrest, Run!


Ever need to run for a while, when you were, I don’t know, doing cardio or playing a sport!? Slow twitch muscle fibers are your best friend when running for distance, let me explain. Your slow twitch muscles are great for endurance activities like long distance running, cycling, and sports such as soccer. These muscles can perform work for a substantial amount of time without fatigue. Remember from my fast-twitch blog, fast twitch muscles are good for rapid movements like jumping or sprinting. They contract quickly, but get tired fast, and they consume an enormous amount of energy.

Your muscles, for the most part, are made up of a mixture of both slow and fast twitch muscle fibers. The amount and type of muscle fibers differ by individual of course. Interestingly, your soleus muscle, located in your lower leg, and back muscles that are involved in maintaining posture, contain mainly slow twitch muscle fibers.

Muscles dense with slow twitch fibers are considered red, because they contain numerous blood vessels. Slow twitch muscle fibers require a robust, oxygenated blood supply as they use oxygen to produce the energy needed to contract.

​​About Slow-Twitch Muscle Fibers 
  1. Slow-twitch fibers contain mitochondria, which are organelles that use oxygen to create adenosine triphosphate (ATP), which is the chemical energy that fuels muscle contractions. This is the reason slow twitch fibers are considered aerobic (use oxygen).
  2. Slow-twitch fibers are also called red fibers because they contain more blood-carrying myoglobin, which creates a darker appearance.
  3. The slow twitch muscle fibers produce their own source of energy, and can maintain an exerted force for an extended period of time, however they are not able to generate a significant amount of force.
  4. Slow-twitch fibers are the first recruited when a muscle contracts. Pending their ability to generate the amount of force necessary, the fast-twitch muscle fibers are engaged.
  5. The muscles responsible for maintaining posture have a large amount of slow-twitch fibers.
  6. You could increase mitochondrial density in these muscles via steady-state endurance training. This type of training will improve your body’s ability to use oxygen to produce ATP. 


Isometric contractions, little-to-no joint movement, will cause constant contraction in your slow-twitch muscle fibers and can help improve their ability to utilize oxygen to produce energy. Example exercises: single-leg balance, front plank, side plank.

  1. Circuit training, alternating from one exercise to the next with little-to-no rest (using light weight), will challenge slow-twitch fibers.
  2. High-repetition body-weight exercises are an effective way to improve aerobic metabolism, in turn improving the efficiency of slow-twitch fibers.
  3. Short rest intervals of approximately 30 seconds between sets will challenge the slow-twitch fibers. 
  4. Use lighter weights with slower movement tempos and high repetition (15+) to engage the slow-twitch fibers. This keeps your body in a state of aerobic metabolism while fueling the activity.


To summarize, slow-twitch fibers have unique functional characteristics, and they can be trained to be more aerobically efficient, with the proper exercise program, of course.



This article was provided by PT by CV
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