Skip Nav
Shopping Guide
Yo, Amazon Prime Has Insanely Cheap Workout Clothes (and They're Actually Really Cute)
FitFinder
We've Found Your Next Workout
Personal Essay
I May Never Be Skinny, but Weight Watchers Keeps Me Healthy

Muscle Types: Slow Twitch vs. Fast Twitch

Don't like sprinting? Blame it on your muscles. Deep within your skeletal muscles you have different twitch fibers. Although this makes it sound like your muscles are textured like different knitting stitches, in truth the muscle twitch fibers ultimately look the same, but they work differently.

Slow twitch fibers (aka type I fibers) are the part of the muscle made for endurance activities like walking, running, and biking long distances. These are the muscles of tai chi. Fast twitch (aka type II) muscle fibers are made for quick bursts of movement, like sprinting or kicking a soccer ball.

Our genes determine if we have more of one type of fiber over the other. Regardless, you need to work them both. One way is to vary the speed of your lifting, adding fartlek into your runs, or doing a change-up with weights and repetitions when strength training. To do this, try lifting a lighter weight for more reps, then a much heavier weight for fewer reps.

Feeling twitchy? Go on, work out, and strengthen all your fibers — fast and slow.

Image Source: Getty
Around The Web
Join The Conversation
runningesq runningesq 7 years
Pfitzinger goes into this in his book, Advanced Marathoning.
sunshinepointe sunshinepointe 7 years
This is awesome - I'm taking my AFAA certification for group fitness and I just read the chapter about musculoskeletal anatomy. A great surprise and very well written for those who don't know!
What can one pound of muscle do for you?
Four Active Family Weekends to Explore
How Muscles Are Made
Post Baby Workout
New Celebrity Moms 2017
Are You Strong on Muscle Knowledge?
70-Year-Old Woman Runs 7 Marathons on 7 Continents
Definition: Isometric Exercise
Alessandra Ambrosio's Best Workout Outfits
To Ice or to Heat?  That is The Question

POPSUGAR, the #1 independent media and technology company for women. Where more than 75 million women go for original, inspirational content that feeds their passions and interests.

From Our Partners
Latest Fitness
All the Latest From Ryan Reynolds