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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
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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!
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