Muscle Fibers Part 2 – Why We Should Train Our Fast-Twitch Muscle Fibers

Muscle Fibers Part 1: Slow Twitch Muscle Fibers


We’ve talked about the importance of training slow-twitch muscle fibers, especially for endurance athletes. Regardless of the ratio, we all have fast-twitch muscles that we can’t neglect. Understanding fast-twitch muscles and how they affect performance will help you incorporate training them into your regimen to give you the best results for whatever you’re training for.


Fast-twitch muscle fibers are the largest and most powerful in the body and store a great deal of carbohydrates. They have much lower endurance but exert more force than slow-twitch fibers.


2 types of fast-twitch muscles:


Type IIa – the middle of the muscle fiber spectrum, less fatigue resistant, produce more muscular force, and contract at a faster speed than slow-twitch fibers.


Type IIb – the last muscle fibers to be recruited during activities that require an all-out burst of power for a short period of time and produce maximal strength.


All easy running is handled by slow-twitch muscle fibers. As running intensifies, more and more fast-twitch fibers are recruited (type IIa first followed by type IIb). Regardless of whether you’re working on your short or long-distance training, you need to incorporate a mix of fast-twitch workouts to make sure they can come to the rescue when you need them.


Training fast-twitch muscle fibers


Speed work


Short repeat intervals – traditional interval workouts help recruit intermediate and fast-twitch muscle fibers. By being used together, these two fiber types learn to interact more efficiently.

Sprint work – hill sprints and maximum effort sprints help recruit the maximum amount of fast-twitch muscle fibers. Even for long-distance runners, speed work is important to make each stride more explosive, helping you get more bang for your buck with a maximum efficiency stride.


Strength training


Fast movements – box jumps, jump squats and kettle bell swings help target and train fast-twitch muscles for explosiveness.

Heavier power exercises – exercise like power cleans and back squats focus on the power side of your type IIb fast-twitch muscle fibers. These are the gym equivalent of short distance sprint work for your fast-twitch training. 


When you’re lifting, lift as fast as you can at lower reps. If you’re an endurance athlete and you’re a little hesitant to add too much weight when lifting, focus on explosive, high intensity exercises instead. It’s important to remember that working on your fast-twitch muscle strength isn’t going to turn you into a bulky body builder unless you stop all of your endurance training.


Hopefully you’re sold on why you shouldn’t shy away from training your fast-twitch muscle fibers. Don’t worry…you won’t turn into the Hulk or even get a sprinter’s physique as long as a majority of your training continues to be high mileage and slow-twitch training.


Here are a few resources for more info on fast-twitch training:


3 ways to develop fast-twitch muscles

How do I target fast-twitch muscle fibers?

Use your muscles to run


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