What Your Muscles Are Really Made Of

Take hold of your health with our Fitness Director, Clint Ward.

Slow Twitch & Fast Twitch

You might have heard that muscles are made of muscle fibers. There are two different types of muscle fibers within the human body: slow twitch (Type I) and fast twitch (Type IIa & IIb). We typically contain 50% of both as they are mixed within bundles of each other.

Slow twitch fibers (Type I) are smaller in size and contract at a slower rate, but can continue to do so over a longer period of time as they utilize oxygen as a source of fuel. If you’re looking to create the “leaner” look then you need to take this into consideration during exercise. A higher rep count in the gym or a longer run outside will challenge these slow twitch fibers and help keep your lean tissue smaller in size.

Fast twitch fibers (Type IIa & IIb) are larger in size and contract faster than Type I, but fatigue quickly. People who train at sprints or explosive power lifting are targeting their fast twitch fibers. This helps create bulk in the body. Type IIa is a hybrid of both fibers. If you’re looking to increase size just remember to train technique before you train speed. Accelerated reps increase your risk of injury if you fault on your form.


Don’t be afraid to train fast if you are still trying to lean out. Most of your workouts can consist of long distance runs, swims, or high rep lifts but you should incorporate a fraction of your week to fast twitch training in order to target all muscle fibers and get full benefit of the human body.  Same is true the other way around, powerlifters need to find a trail and challenge their endurance at least once a week.

Training fast also has its benefits for keeping lean. Here are just a few:

  1. Increased Metabolism – Increasing your heart rate and maximizing your work output requires a greater metabolic demand in all fuel sources. (Burning Fat, Sugar, Protein, and Creatine)
  2. Increased Cardiovascular System – Your heart will increase its ability to deliver blood and oxygen to all the systems more efficiently. The greater the oxygen supply, the greater the fat burn.
  3. Sparks Neurogenesis – Synapses are fired at an accelerated rate, extra blood is delivered to the brain, and new brain cells are created. This process helps to increase coordination, balance, and energy which are all benefits that carry over to endurance exercises.

There is nothing you can do naturally to build more muscle cells. Muscle cells are mainly filled up with water, protein, and sugar. Most people are dehydrated, which will make the cells smaller than they should be. If you’re exercising but not replenishing your water, sugars, and protein, then your lean tissue can shrink in the process.

The reverse is true for those trying to stay lean. You will enlarge your lean tissue as you flush water into your cells. Muscles will soak up the water and sugar like a dried up sponge after an hour of exercise. Your muscle may naturally be bigger than you think.

Keep up the good work! Remember that an efficient program consists of 70% diet and 30% exercise. None of this works without putting the proper nutrition into your body. Cheat days should be few and far between!


Clint Ward

Fitness Director