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Jacob Wilson Ph.D., CSCS
Skeletal Muscle Physiologist

Ask the Muscle Prof

"How do I target fast-twitch
muscle fibers?"

Ask The Muscle Prof: How Do I Target Fast-Twitch Muscle Fibers?

Fast-twitch muscle fibers aren't just important for sprinters and competitive weightlifters. Here's what they have to offer bodybuilders!

Q
I've heard that fast-twitch muscle fibers are the largest in the body. How can I target these in my training to help me build mass?

You heard right! Fast-twitch muscle fibers are indeed the largest and most powerful muscular movers in your body. Unfortunately, they're also neglected in most bodybuilders' programs. It's time to change this!

The human body is equipped with a variety of muscle-fiber types. These range on a spectrum from the smaller, endurance-based, slow-twitch fibers to the larger fast-twitch fibers designed for strength and power activities. But you're right that these larger fibers have physique implications as well. Aside from their sheer size, fast-twitch fibers also store a great deal of carbohydrates. For every gram of carbohydrate you store, you also draw about 3 grams of water into the muscle. Thus, bodybuilders who optimize fast-twitch fiber development will obtain a fuller and denser look onstage.

The balance of fast-twitch and slow-twitch fibers in your body is determined by genetics, but there's still plenty you can do in your training to maximize growth and strength in the muscles you have. Specifically, consider two variables when trying to activate fast-twitch muscle fibers: the amount of weight you lift and how you manage fatigue during sets.

Go Heavy!

Your body recruits muscle fibers based on the force demands placed upon it. If the force demands from an exercise are less, you'll use more slow-twitch fibers. The greater the intensity—meaning percentage of your one-rep max, not just how strenuous an exercise feels—the more you'll tap into fast-twitch fibers.

In 2004, researchers found that powerlifters and Olympic weightlifters had much greater fast-twitch muscle-fiber development than bodybuilders.1 It's at least partially a question of programming. The traditional bodybuilding program focuses on the 8-12 repetition range with moderately heavy loads and 60-90 seconds of rest between sets. Compare this with powerlifters, who train largely in a 1-5 repetition range with very heavy weights and 3-5 minutes of rest. Studies show that individuals who neglect training in a heavier range will not program their nervous system to effectively recruit their largest fast-twitch fibers.2

The greater the intensity the more you'll tap into fast-twitch fibers.

But it's also true that in the original study, bodybuilders still had larger overall muscle size. This is because, unlike powerlifters, they had also drastically increased the size of their slow-twitch muscle fibers. Based on this research, it is clear that bodybuilders looking to maximize gains should incorporate heavy low-rep training sessions in addition to the traditional 8-12 repetition range for improved fast-twitch muscle fiber development, and thus greater growth.

Fatigue Is Your Friend

Along with intensity, fatigue is the second surefire way to increase fast-twitch muscle fiber recruitment. Your body's first impulse is to recruit slow-twitch fibers, but once you fatigue those fibers, it has to recruit fast-twitch fibers to do what is being asked of it.2

Making the most of this phenomenon is more a matter of how you train rather than what your program looks like. For example, most lifters take brief rest periods between repetitions when a set becomes painful. When you do this intentionally, it is known as cluster set training, but what I'm talking about is largely subconscious, such as when a subject in my lab pauses between reps during a difficult set of squats.

After seeing it countless times, my colleagues Jordan Joy, Ryan Lowery, and I decided to study what happens on squats when you mimic this natural intra-set rest technique.3 We had athletes perform 4 sets of 8 maximal repetitions either with or without brief rests in the middle of the set. We found that intra-set rest decreased fatigue, but it also prevented the body from recruiting the fast-twitch muscle fibers.

The take home message here is to analyze how you perform a given set. If you find yourself pausing when a movement gets difficult, you may be short-changing your gains!

Make this principle work for you throughout a workout by keeping your workout density high. Here's what I mean: An athlete who takes 2 hours to perform 15 sets has low density, while an athlete who performs 15 sets in 30 minutes has extremely high density. By shortening your rest periods on traditional bodybuilding days, your slow-twitch muscle fibers will fatigue much sooner and fast-twitch muscle fiber recruitment will skyrocket.

Make Fast-Twitch Fibers a Priority

The existing evidence strongly supports the conclusion that heavy lifting and muscle fatigue largely dictate the recruitment of fast-twitch muscle fibers. To put these principles into action, perform a heavy training day every 2-3 workouts. A good training split for a given body part could look like this:

  • Workout 1: Heavy, 1-5 repetitions, 3-5 minutes rest, compound movements
  • Workout 2: 8-12 repetitions, 60-90 seconds rest, mainly compound movements
  • Workout 3: 12+ repetitions, 30-60 seconds rest, supersets, compound and isolation movements
Keep fighting and pushing, and your body will adapt accordingly.

On heavy days, prioritize movements that recruit the most muscle, such as squats, deadlifts, bench presses, shoulder presses, dips, and pull-ups. On your 8-12 repetition days, keep workout density high and hammer out repetitions one after the other. Regardless of the pain you may experience, don't pause in the middle of a set.

If it helps, remember one of my favorite quotes from Lance Armstrong: "Pain is temporary. It may last a minute, or an hour, or a day, or a year, but eventually it will subside and something else will take its place. If I quit, however, it lasts forever." Keep fighting and pushing, and your body will adapt accordingly.

Now get out there and lift some heavy weight!

References
  1. Fry AC. The role of resistance exercise intensity on muscle fibre adaptations. Sports Med. 2004; 34(10): 663-679.
  2. Gabriel DA, Kamen G, Frost G. Neural adaptations to resistive exercise: mechanisms and recommendations for training practices. Sports Med. 2006; 36(2): 133-49.
  3. Joy, J.M., Lowery, R.P., & Wilson, J.M. Effects of intra-set rest intervals on muscle activation and power. National Strength and Conditioning Conference; 2013 July 10-13; Las Vegas, NV.

Related Articles

About The Author

Dr. Jacob Wilson, Ph.D., CSCS*D is a professor and director of the skeletal muscle and sports nutrition laboratory at the University of Tampa.

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Mudvayne24

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Mudvayne24

Great article as always. Keep the science coming.

Jan 17, 2014 6:48pm | report
 
DrJacobWilson

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DrJacobWilson

Thanks buddy!

Jan 20, 2014 2:52pm | report
hamlifer

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hamlifer

Love learning new things. I'll definitely be paying attention to the rests in my sets to maximize the recruitment of those fast-twitch fibers!

Jan 17, 2014 8:36pm | report
 
oceanbeauty

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oceanbeauty

Awesome article. Will definetely keep this advice in mind for my next few workouts

Jan 17, 2014 9:28pm | report
 
AutumnHB

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AutumnHB

good read.

Jan 17, 2014 10:44pm | report
 
Miamiboy87

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Miamiboy87

So when I'm lifting some heavy weights and I freeze on my 5th rep , still push?.

Jan 17, 2014 11:15pm | report
 
DrJacobWilson

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DrJacobWilson

I would buddy

Jan 20, 2014 2:52pm | report
faiznmatazzz

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faiznmatazzz

Thank you once again for the great ARTICLE!

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Jan 18, 2014 12:21am | report
 
DrJacobWilson

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DrJacobWilson

You bet!

Jan 20, 2014 2:54pm | report
ThatDudeCheek

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ThatDudeCheek

Thanks for the advice, I'll remember this today when I'm doing legs.. No pauses on the squats push through :'(

Jan 18, 2014 2:33am | report
 
IMANI44

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IMANI44

Good article , when I hit the gym today go heavy short rest periods! Thanks

Jan 18, 2014 4:54am | report
 
DrJacobWilson

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DrJacobWilson

You bet!

Jan 20, 2014 2:54pm | report
thejinfection5

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thejinfection5

interesting, will keep this in mind

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Jan 18, 2014 7:07am | report
 
dchampisere

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dchampisere

Excellent article! This is exactly what I am doing for the last 3 months and have been getting insane results.

Jan 18, 2014 10:37am | report
 
DrJacobWilson

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DrJacobWilson

Right on pal!

Jan 20, 2014 2:55pm | report
TushkaTraining

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TushkaTraining

Doc Wilson is always on point!

Jan 18, 2014 11:14am | report
 
DrJacobWilson

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DrJacobWilson

Thanks pal appreciate it!

Jan 20, 2014 2:55pm | report
jittspatel

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jittspatel

learned something new today!!!

Jan 18, 2014 12:47pm | report
 
Whey2B

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Whey2B

Really great read! Will make a tweek or two to my routine to see if this will benefit my overall gains

Jan 19, 2014 7:11am | report
 
ChewGainz

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ChewGainz

Great article thanks. I will incorporate this into my routine. Gotta love science!

Jan 19, 2014 7:33am | report
 
Al3xmr

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Al3xmr

ready to get this into my routine

Jan 19, 2014 8:28am | report
 
Krutselno

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Krutselno

Interesting, I'll try to not stop in the middle of my set during bench press today.

Because of time I usually incorporate heavy sets with longer breaks and easier sets with shorter breaks during the same workout, is that the wrong way to do it?

Jan 19, 2014 9:38am | report
 
DrJacobWilson

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DrJacobWilson

Well its ok to rest between heavy sets longer, but within the set try and avoid too many pauses so you maximize motor unit recruitment

Jan 20, 2014 2:56pm | report
DrJacobWilson

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DrJacobWilson

Well its ok to rest between heavy sets longer, but within the set try and avoid too many pauses so you maximize motor unit recruitment

Jan 20, 2014 2:56pm | report
Bijad

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Bijad

very very well done... i really like this article thx prof.

Jan 19, 2014 9:59am | report
 
Showing 1 - 25 of 40 Comments

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