3 Main Categories of Muscle Fibers!

At one point in time, everyone hears or reads of this “cure all” super workout that they just have to try. One of those workouts that is supposed to solve all of life’s problems, add 100 pounds to your Deadlift, drop 6 inches off the waistline or turn you into a Greek God all with just  30 minutes a day.

Well sure why not? Some try it and get amazing results others try it and get virtually nothing. Why is that?

One Answer = Muscle Fiber type

Different muscles in the body are made for different things and therefore have to vary in their makeup. Some were created to produce massive amounts of power over a short period of time, some are made to sustain power overlong period of time and some are made to do a little bit of both.

Just as from muscle to muscle, muscle fiber type varies from person to person. For example an Olympic sprinter has different fiber type dominance than an Olympic marathon runner. The sprinter can have as much as 80 % fast-twitch muscle fibers whereas the marathon runner can have as much as 80 % slow-twitch muscle fibers. This fiber type difference or muscle makeup difference means that a sprinter may need to work their same muscles out under a different load for a different amount of time than a marathon runner on the same exercise to get results. Most of us are somewhere in the middle of that spectrum of either more fast-twitch more slow-twitch or more mixed fiber type.

So What Exactly Are They?

There are 3 main categories of muscle fibers. Type 1, Type 2A, and Type 2B muscle fibers.

Type 1

• These muscle fibers are what we call slow-twitch muscle fibers.  These fibers are the first to fire, basically meaning they fire under low loads, and are made to sustain their contraction over long periods of time.
• These fibers are smaller in diameter than the fast twitch fibers. They use and store less glycogen or sugar and rely more on oxygen transport for fuel. For example the 50 + rep range. These muscles are usually the postural muscles or the muscles that hold you upright, that need to be able to contract over and over.
• The Soleus in the calf, the “core muscles” abdominals, muscles of the lower back, the Spinal Erectors, the Quads, the muscles surrounding the scapula and shoulder just to name a few have to hold and stabilize joints and structures for longer periods of time. They need to be able to contract and hold at lower threshold power. These muscles recover quickly and need to be worked for longer periods 2-4 sets at high rep ranges of 21 or more with shorter rest intervals around 30 seconds.

Type 2A or fast-twitch A

• As the weight/load increases, these muscle fibers get recruited and start to fire. Fast-twitch muscle fibers are larger in diameter than slow-twitch but rely more on storing larger amounts of creatine-phosphate and glycogen for fuel which do not last as long.
• These muscles respond best under a load that is equivalent to around 3-5 sets of 7-10 repetitions. These are the typical rep ranges that you will find most people doing.
• These fibers need more recovery than slow-twitch but not as much and your type 2B’s.  Somewhere around 1-2 min's usually does the trick.

Type 2B or fast-twitch

• Now, if the weight/load you are trying to lift becomes to heavy, Type 2B muscle fibers get recruited and start to fire. These fibers are thicker and more powerful than the Type 2A’s.
• 2B’s fire only when the Type 1, and Type 2A’s are firing at their highest rate (failure). Therefore when the Type 2B’s fire all of the types of muscle fibers are firing. These muscles fatigue the fastest but when they fire they create the most amounts of force.
• They fire under a load that is equivalent to  around 90% of a maximal load or around a weight that you could lift for 1-6 reps.
• Some examples of muscles that tend to be more fast twitch are your Triceps, Hamstrings and the Gastrocnemius of the calf.

When you are working type 2B fibers, you are recruiting so much muscle that your central nervous system has to coordinate a ton of different muscles and many different fibers all at the same time.  This type of work, causes a massive stress on the CNS.  Keep in mind, that it takes an average of 5-6 times longer for your nervous system to recover than your muscles.

• When you are working with HEAVY weights, you should keep your rep range around 1-4 over 5-10 sets and take a longer rest period in between.  Typically 2-5 minutes for most.  Obviously the more advanced and fit you become, the better your body will adapt.

The Bigger Picture

 
If you think about it the calf has a slow twitch muscle the smaller deeper Soleus for balance, stability and support and a fast twitch muscle the bigger more powerful Gastrocnemius for speed and power production. When we think arms we look at the biceps and triceps. The biceps have to contract and help raise the arm all day, against gravity therefore they need a makeup closer to the slow twitch side of the spectrum, whereas the triceps on the back only have to extend the arm when gravity does not do it for us therefore they do not need to fire and sustain for as long.  They are there for just hard and fast when we need it.
You will find pairings like this all over the body. The Hamstrings and Quadriceps are another example. The hamstrings in the back of the leg (made up of four muscles) are usually some of the most fast-twitch dominant muscles in the body made for power and acceleration to get you moving, whereas the quadriceps (made up of four muscles) and the muscles that keep you erect and keep movement going over and over are usually more slow-twitch in nature. Most of the joints in the body are supported by both slow and fast twitch musculature.
Conclusion:
So at the very least a balanced program that mixes workouts at the 15-20 range rep range, the 8-10 rep range and the 2-6 rep range will allow firing and muscle growth for all the muscle fibers.  Make sure to mix things up and change out your workouts on a regular basis.