Time for our Workout Of The Month. Each month we take a look at a different exercise and break it down by movement, how to do it, and discuss some of the positive versus negative impact that it can have to you and your level of fitness. Some workout’s of the month breakdown how to do a common exercise, others feature a specific workout. This month is back to basics: talking about muscle fiber types and why muscle fiber types should matter to you.

Muscle Fiber Types In A Nutshell

As you could assume, there is more to a muscle than just a muscle. Our muscles are responsible for several types of contractions: concentric, eccentric, and isometric muscle contraction. Each type of contraction is responsible for different movements and helps to build strength and reduce the risk of injury in various ways.

Within our muscle makeup are also three types of muscle fibers:

Type I Slow Twitch Muscle Fibers
Type IIA Fast Oxidation Muscle Fibers
Type IIB Fast Glycolytic Fibers

Each muscle type is responsible for producing a certain type of force in your body. In addition to the force, each one requires a certain type of energy as a fuel sources as well. I’ll get more into that below.


Why Muscle Fiber Types Matter To You

Are you a better sprinter or a better endurance runner? Based on what your answer is, your muscle fiber type is responsible for what you picked. Another question: what happens when you don’t use a muscle? It gets lazy. Eventually your body recognizes that it’s no longer needed and it gets smaller and weaker. The same is true if you’re not using all your muscle types for what they’re designed for. What if I also told you that, by eating the wrong kind of food and training the wrong type of muscle fiber would make your workout’s suffer?

Since each type of muscle fiber type is responsible for delivering a specific amount of force, they also require a specific type of fuel in order to work for you.

Type I Slow Twitch Muscle Fibers

Type I muscle fibers are your slow twitch muscle fibers. These types of muscles are responsible for movements that don’t require a lot of force and for muscles that can contract for long periods of time. For example, a prolonged long jog, or a long stand-up paddle board session would be examples of muscles fiber types that you would be recruiting during this type of exercise. Moving a fork from a plate to your mouth would also qualify for slow twitch muscle fiber types.

Energy Source For Type I Muscle Fibers:

Since type I muscle fibers need to go for prolonged periods they require aerobic exercise to generate most of the energy for their contractions. Because these muscle fibers are required to go for longer distances, they’re unable to move larger amounts of weight compared to other muscle fiber types. These fiber types also need a larger energy source. Ideally, you want fat to be your primary source of energy for these muscle fibers. But these muscle fibers will also draw upon sugar in the blood as well as stored sugar in the muscles and liver.

Type IIA Muscle Fibers

These are thought of as muscle fibers in between type I and type IIB muscle fibers. These muscle fibers can move a moderate amount of strength and power but because of their makeup, they can only generate a specific amount of strength for a certain period of time. Think of running at a fast pace or being in a gym lifting weights for eight to fifteen repetitions. These muscles operate under both aerobic and anaerobic exercise.

This type of muscle fiber uses primarily sugar to generate it’s energy and the activity of the muscles can only sustain themselves for about thirty to sixty seconds of exercise before the workload will have to be decreased. Eventually the workload will have to turnover to slower or lighter activity and type I muscle fibers will takeover.

Type IIB Fast Glycolytic Fibers

These type of muscle fibers are your workhorses of your muscle fibers. These muscle fibers are responsible for producing brute strength, force, and quick movements. Think of burpees at a fast pace, plyometrics, box jumps, all out sprints, or jumping out of a car to avoid being struck. These muscle fibers are recruited when you’re going all out attempting to reach your one rep max at the gym or explosive exercise on a field. These muscles fiber types use neither fat or sugar for their energy.

Type IIB muscle fiber types use anaerobic exercise as their energy pathway and a stored form of energy called ATP The ATP used for type IIB muscle fibers is very limited and only stored in the muscles. This type of force and power is only available for short periods of about ten seconds. After that workload has to be decreased because type IIA muscle fiber types and eventually type I muscle fibers.