Optimize Results with Fiber Training

Fast twitch fibers, slow twitch fibers, intermediate fast twitch fibers. While we may have heard these terms before, we need to understand the practicality and applicability of them in regards to training for sport. In order to train the right muscle fibers, we need to first discuss what constitutes fast and slow twitch muscles.

We have over 600 muscles in our bodies, all made up of a mixture of fast twitch and slow twitch muscle fibers. We are going to start with the big picture, dive briefly into some physiology, and go back to big picture. This will help you to better understand fiber type training.

Within one motor unit (muscle), we can have anywhere from 10-1000 muscle fibers, depending on which muscle group we are talking about. The glutes, a large muscle group, are going to be on the higher end in terms of the amount of muscle fibers it has, while the orbicularis oculi (muscle around the eye) is going to have fewer fibers. While the actual ratio of fast:slow fibers depends on a variety of factors, let’s keep it simple and just know that every muscle has a both types of fibers. Now, within a motor unit, individual fibers contract when they are stimulated to do so. However, the type of fibers that contract are dependent on the stimuli, or type of contraction you are doing. Here is a quick description of the 3 pure fiber types.

Slow twitch type I– Smaller muscle fibers in size. High aerobic capacity and high resistance to fatigue. Anywhere from 10-180 of these fibers per motor unit. Generally, you would think of long distance runners as the athletes having a large percentage of slow twitch fibers.

Intermediate fast twitch, type IIa– Larger muscle fibers in size. Moderate aerobic capacity, higher (relative to type I) anaerobic capacity. These fibers fall somewhere in between the long distance runners and the high intensity, explosive athletes. You may consider these your strength/power endurance fibers.

Pure fast twitch, type IIx– Largest muscle fibers in size. Low aerobic capacity (fatigue quickly), high anaerobic capacity. Great at producing high force for short amounts of time. Football players are an example of an athletic population with a high percentage of fast twitch muscle fibers (plays generally last 5-10 seconds at most).

If you are training for a marathon, which places a high demand on your aerobic energy system, your type I fibers, how often should you be performing squat jumps?

In contrast, if you are a shot putter, do you think running 5 miles a day, or performing 20 rep bench press  are going to help improve your max distance? Of course not!!!

You need to train the right fibers more often than the “wrong” ones! Every athlete needs to train all fibers, but some more-so than others depending on your goals. If your sport requires you to be fast, train fast. If you want to be powerful, then you must emphasize your fast twitch fibers, with the majority being type IIx. A volleyball player has no business running 3 miles at a submaximal pace (not often at least). Just as a cyclist should not be squatting heavy 3 days a week. When you do this, it is not only inhibiting the necessary energy systems from developing, but it is often counterproductive. Think about how effective an 18 wheeler would be with a 4 cylinder engine…

What about the athletes that need to be fast and explosive, but sustain that over long periods of time? These are your soccer, basketball, hockey players. The majority of their fiber training needs to be focused somewhere in the middle of the continuum, but more towards fast twitch. The intermediate fast twitch fibers are most effective for their sport. Eric Cressey, a highly respected performance coach, spoke in regards to off season training, saying that you have to learn to go fast PERIOD before you can sustain that speed for an entire game. Therefore, a basketball player needs to focus on fast twitch training and getting stronger more before he worries about his strength endurance.

Here is video of an exercise where the athlete starts out using mostly type IIx fiber  (type I are always recruited first as we saw in the graph) , but starts relying more on his intermediate type IIa and type I fibers as fatigue begins to set in.

While fiber type training is extremely important to the principle of specificity, we still need to have an open-minded approach and train to be optimal. An optimal athlete, whether you are playing an aerobic or anaerobically demanding sport, has to train all fiber types by utilizing all energy systems. If a football player NEVER imrpoves his strength endurance, he will get beat in the 4th quarter when it counts. If an ultra-marathon runner NEVER lifts a heavy weight to strengthen fast twitch muscles (the largest muscle fibers in size as previously noted), it is impossible for them to be as fast as possible for as long as possible.

The take home message is to allocate your time spent training muscle fiber type according to the of the demand of your sport.

In regards to calorie expenditure and weight loss, fiber type training is king. Because muscular contraction yields energy expenditure, wouldn’t it make sense to contract as many muscle fibers as possible? If your body allows you to do so, and you have no functional limitations, it makes sense to train your muscles to experience fatigue so that you HAVE to recruit more muscle fibers.

Next time you hit the gym, consider your goals. Do you want to be fast and explosive? Enduring? Fast for a long period of time? Toned? Muscular? All of these goals can be attained if you adhere to the principles of fiber type training. But remember, to be optimal, a complete 360 degree circle, you need ALL 8 of the essentials…


Train smart!

Andrew Simpson IYCA-YFS

368 Athletics


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