Over the last 7 years of personal training and instructing, I’ve noticed that those who actually activate their fast-twitch fibers during training, tend to be the most successful with their weight loss goals, compared to those who don’t.

In this article, you’ll discover:

  • What fast-twitch fibers are
  • How they help you lose weight
  • How to actually activate them (which also helps develop more of them)
  • Other benefits of training fast-twitch fibers
  • How to incorporate this training in your next workout

What Are Fast Twitch Muscle Fibers

Every muscle in your body consists of 2 types of muscle fibers: slow-twitch and fast-twitch. For the non-athlete person, typically each muscle in the body will contain 50 percent slow and 50 fast.

Fast-twitch fibers are used during more short-duration exercises. So think of a sprinter in track. These types of athletes have a majority of fast-twitch fibers because the events they train for typically last less than a minute. Marathon runners, on the other hand, have a higher ratio of slow-twitch fibers. Any exercise lasting more than a minute will be performed by a majority of slow-twitch fibers.

Other types of athletes that incorporate more fast-twitch fibers would be football players, Olympic weightlifters, basketball players, tennis players, and baseball players. You get the idea.

How Fast Twitch Fiber Activation Helps You Lose Weight

So what you may already know, to lose weight, you must burn more energy than you’re putting in. Also, it’s important to know that fat cells in your body are stored energy.

The major difference between fast and slow-twitch fibers is how they utilize energy. Fast-twitch fibers need energy now. They get it fast and they burn it fast. Obviously, with slow-twitch it’s opposite. They don’t need it now, but when they do get it, they burn it slowly. It’s like the difference in fuel economy between a semi-truck and a hybrid car.

So, now that you know fat = stored energy, which fiber do you think is going to burn through that stored energy quicker? The answer is the fast-twitch fibers.

But it’s important to know, by default, your body uses the slow-twitch fibers. So that’s why it’s essential to your weight loss goal to learn how to activate your fast-twitch muscle fibers while you’re at the gym.

How To Activate And Develop Fast Twitch Muscle Fibers

There are only 2 ways to activate fast-twitch fibers during your workout:

  1. Do explosive movements.
  2. Lift heavy.

The great thing is, just about any exercise that you’re doing can be done heavier, and sometimes can be done in an explosive manner. And this is exactly what I encourage you to do.

But, despite my encouragement, what I usually see is that people are scared to lift heavier due to the thought that heavyweight makes you look “bulky”. Over my 7 years of training, I’ve yet to see anyone attain this “bulky” effect after adding some fast-twitch fiber training to their routines. But what I do see, is people losing weight and keeping it off.

So what does heavy look like? A good rule of thumb is to choose a weight that you can do between 3 to 6 reps of, for at least 4 sets. That means if you choose a weight and you hit 6 reps, and figure you can do more— you need to stop and go heavier.

If you’re looking to do more explosive training, consider movements like sprints, box jumps, jump squats, KB swings, or Olympic lifts. Typically, I don’t suggest these without teaching proper technique first (with sprints as an exception), as they require more coordination compared to basic weightlifting exercises.

I’m a big fan of incorporating explosive movements in with high-intensity cardio. As I’ll explain more in the benefits section below.

The more and more you activate fast-twitch fibers over several weeks of training, you’ll likely see an increase in strength, meaning you’re developing more of these fibers.

Other Benefits Of Training Fast Twitch Muscle

  • Burn fat while resting. When you train these muscle fibers through heavy lifting, they not only require more energy during exercise, but your body must replenish these fibers with energy after your workout is over. So if you don’t give them that energy from food, they’ll get it from your fat stores.
  • Decreased negative aging effects. One of the major reasons we have issues as we get older, with bone density and joint strength specifically, is because our body turns fast-twitch fibers into slow-twitch fibers as part of the aging process. So training fast-twitch fibers will help decrease the rate of the aging process.
  • Combine explosive movements with high-intensity cardio and you’ll be burning fat for hours after your workout is over. Science has shown that high-intensity interval training has a “post-exercise oxygen consumption” effect. What this basically means is that your body will be burning energy to recover well after your workout is over. Adding explosive movements in with this type of cardio, and you’ll increase this calorie-burning period.

How To Incorporate Fast Twitch Fiber Training Into Your Routine

To begin, I want you to know that fast-twitch fiber training is not the ONLY training I suggest. I recommend it as a portion of your whole workout. In fact, a workout for weight loss or just general fitness should consist of both fast and slow-twitch training through lifting weights, as well as both steady-state and high-intensity cardio. I’ll teach you how to form your own workouts in another article.

When it comes to training your fast-twitch fibers through heavy lifting, I suggest beginning with the exercise you plan on doing. Squats, deadlifts, bench press, barbell rows are all great exercises to do heavy lifts with. And as always, make sure you do 2 or 3 warm-up sets before you begin your first heavy working set.

For a day focusing on legs, you could begin with squats, doing 4 sets of 6 reps. And remember, if you hit that 6th rep and figure you can do 7 or 8 reps with it, go heavier on the next set. And when lifting heavy, rest 2-3 min between sets (as you get stronger, you may find you need more rest to hit your desired rep goal).


If your goal is to lose weight, fast-twitch fiber training may be a great addition to your workout routine. When done correctly, it can burn more calories in a shorter amount of time and cause your body to burn calories after the workout is over.

Incorporate fast-twitch fiber training by lifting heavy, or adding explosive movements, or both. For maximum weight loss in the shortest amount of time, I prescribe 2 heavy lifts at the beginning of workouts, then finish the workout with 10-15 min of high-intensity intervals incorporating explosive movements.

If you have any questions don’t hesitate to reach out! I offer personal training and 1-on-1 online coaching, both come with a customized workout and nutrition plan to help you achieve your goals. Head to my contact page to schedule a free consultation today!


  1. Stefanie on January 10, 2020 at 3:37 am

    Good stuff John! Thank you!!!

  2. Lisa on January 10, 2020 at 4:24 am

    Technically, we have three fiber types and the evidence has shown you can train changes in type IIa and type IIx; I remember us talking about this and you used to say “they are there Lisa, you just have to train them,” and it’s good advice but more importantly encouraging to anyone at any age in training. Glad you are out there talking fitness again!❤️

    • John Koopman on January 10, 2020 at 4:46 am

      You’re right! Honestly, I figured that would start confusing people if I threw the middle type in. I wanted the training for each to be cut and dry for the beginners.

  3. Lisa on January 11, 2020 at 3:03 am

    Does this mean you’re back in business? You should be coaching/training!!!!!

    • John Koopman on January 11, 2020 at 3:17 am

      I’m personal training at NW Fitness Zone!

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