Developing fast twitch fibers is the panacea for lackluster performance in strength and power oriented athletic pursuits.  Whether you are looking for extra speed to get a leg up on the competition, or looking for extra jump height, fast twitch fibers will help you get there.

On the other side of the continuum are slow twitch fibers, which help endurance athletes with activities such as distance running.  While each fiber contributes more substantially to specific activities, everyone has a balance between the two types.


The seminal work of Costil et al. reported that the average person has about a 50/50 split between fast and slow twitch muscle fibers.  Endurance athletes were measured with up to approximately 90% slow twitch, while anaerobic athletes displayed approximately 60-80% fast twitch fibers.

The underlying physiology demarcating each muscle type provides a compelling theory related to the performance benefit that fast twitch muscles have on anaerobic sport performance.  So if that is the type of athlete you are, it stands to reason that developing fast twitch muscles is the way to go!

In reality, scientists are still discovering a lot about muscle phenotypes, which simply means we don’t yet have an exact definition for what a fast twitch fiber actually looks like.  Some have suggested that fast twitch and slow twitch can be interconverted depending on the training stimulus, while others present muscles on a continuum with more subtle changes occurring, which means you can’t develop fast twitch muscles from slow twitch.

Don’t Get Lost in Scientific Jargon

Years of physiological research leads the athlete trying to develop fast twitch muscles to one conclusion: muscle fibers definitely influence performance, but they are tricky to define.  If your training philosophy focuses too much on fast versus slow twitch fiber development, you might miss out on performance benefits.

Take-home Message

Instead, focusing your training goals on developing a certain aspect of fitness, focus on performance and you will make gains.  If you want to get stronger, focus on a training program to develop stronger muscles.  If you want to get faster, train with recommendations known to enhance speed.  Your muscle fibers will adapt accordingly, but you don’t have to be preoccupied with measuring exact changes.

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(If you are still on the fence about measuring for fast twitch muscle development, look up the procedure for a muscle biopsy and tell me you would rather have someone suck out a chunk of your leg with a huge needle than use a performance related proxy such as sprint speed or maximal strength measurement).

Bigger, Faster, Stronger

A comprehensive training program for developing all aspects of sport performance that utilize fast twitch muscles is far beyond the scope of this simplified article, but the following are some general ideas to get you going down the right path:

1. Resistance Training: Lifting weights to increase strength is a great way to improve fast twitch muscle capacity.  Try using at least 85% of your one-repetition maximum (1RM) and do 2-6 sets of less than 6 reps.

2. Power Training: Focus on the speed of the movement, rather than a maximal amount of weight lifted.  If using free weights, 75-85% 1RM is a great intensity.  Do anywhere from 2-5 sets of 2-5 reps to improve your body’s ability to generate force quickly.

3. Speed Training: Also called interval or repetition training, speed training can last anywhere from 10-120 seconds.  The shorter the sprint, the faster you should go; this type of training requires all-out effort.

         a) If you are doing short repeats, give yourself about 5 times as long to rest between your next repetition (e.g. if you do a 10 sec, >100% effort sprint—rest for 50 seconds before sprinting again).

          b) If you are doing longer intervals – 60+ secs – make your rest period the same as your sprint time.  For interval training, anywhere from 3-6 intervals can be used to develop fast twitch muscles.  Much more than 6 reps and fatigue starts to change the effort output.

          c) There are also a lot of other ways to get creative with different speed training drills.

Ultimately, fast twitch muscles will develop on their own if the training stimulus is oriented around increasing strength and power.  Don’t let yourself get bogged down by the minutia of exercise physiology—just train focusing on high intensity and low volume modalities, and don’t spend as much time on high volume, low intensity exercises.

Read More from WatchFit Expert Justin Kilian.


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