How to Build Muscle Fiber

April 4, 2020

muscle fiber

See Rule #2 of the 10 Rules of Health and Fitness After Age 50.

If you want it to respond, you have to train it. And you're probably missing your type II's.

Muscle Fiber Twitch Speeds

You've likely heard of "slow twitch" and "fast twitch" muscle fibers. That's the two basic groups of skeletal muscle. The "twitch speed" is describing how quickly the fibers contract to produce force. These fibers are also called Type I and Type II muscle fiber. Type I is slow twitch and Type II is fast twitch. There are two types of fast twitch muscle fiber-Type IIa and IIb.

The basic difference in muscle fiber.

Type I are characterized by:
  • low force, power or speed production
  • high endurance
  • and low energy consumption.
Type IIb are characterized by:
  • high force, power or speed production
  • low endurance
  • and high energy consumption.
And Type IIa are somewhere in between.

Intelligent Design

Your body is a marvel of science and engineering and one thing it always wants to do is conserve energy so it will always recruit the fewest amount of muscle fibers it needs to perform a task.

The Type I's are picked first and then more and more are added, if needed, to complete the task. If more force is needed, Type IIa's and then IIb's are added as required.

Walking is a Type I muscle fiber activity. As you walk farther and exhaust some of the muscle, more Type I's are recruited to keep you going but walking never demands Type II fibers.

Picking up a light weight activates Type I's and maybe that's all you need. Add more weight and IIa fibers are engaged. Make it really heavy and your IIb muscle is added to the fibers doing the work.

You get the idea.

So back to your type II's. Sarcopenia, or muscle wasting, really affects(adversely) your fast twitch muscle fiber. 

You really want to activate your fast twitch muscle fiber and keep it intact. It uses a lot of energy, signals your body to release growth hormone and does a lot to keep you looking and feeling  young.

You can only get your type II' to turn on by lifting really heavy (like close to your 1 rep max) or doing something explosive that requires immediate force production.

Like jumping or sprinting.

Which leads you to Rule #3: - Sprint Occasionally

A couple of baseline rules here.
  1. First, don't get hurt. It's really easy to pull a hamstring or Achilles when you haven't done this in awhile (probably years or decades).
  2. Second, don't overdue it. This will break you down (which is good) but ya gotta recover. One a week max for a sprint workout.

Here's a four week intro into sprinting you might consider:


  • 10-minute warm up
  • 10-minute dynamic stretching
  • 1 warm-up lap or 5-minute light jog
  • Jog for 50 seconds
  • Sprint at 50% effort for 8 to 10 seconds
  • Repeat 5 times

  • 10-minute warm up
  • 10-minute dynamic stretching
  • 1 warm-up lap or 5-minute light jog
  • Jog for 50 seconds
  • Sprint at 70% effort for 8 to 10 seconds
  • Repeat 7 to 8 times

  • 10-minute warm up
  • 10-minute dynamic stretching
  • 1 warm-up lap or 5-minute light jog
  • Jog for 50 seconds
  • Sprint at 60% effort for 8 to 10 seconds
  • Repeat 6 times

  • 10-minute warm up
  • 10-minute dynamic stretching
  • 1 warm-up lap or 5-minute light jog
  • Jog for 50 seconds
  • Sprint at 80 to 90% effort for 8 to 10 seconds
  • Repeat 8 to 10 times
  • Don't try blowing off the line at 100% effort like you're racing Carl Lewis. Start with a jog and then accelerate into your pace effort for 8 to 10 seconds and then back off to a walk. Then repeat.

    As always, mix it up and have fun with it.

    If you want to live long with high productivity, keep working your fast twitch muscle fiber. This is where the game is really played.

    Stay Strong.

    Here's a handy pdf with a few other sprint workouts

    #1 - Lift Heavy Things

    #2 - Increase Nutrient Density
    #3 - Sprint Occasionally

    A corollary to Rule #3 is just think dynamic or explosive force production (for alternate workouts). Things like jumping (both vertically and horizontally (standing broad jump), car push, run up steep hills, push a heavy wheelbarrow, power cleans, thrusters (front squat with overhead press), heavy double kettlebell swings, etc. 

    These all will work to stimulate fast twitch muscle.

    Sometimes when I'm hiking, I'll pick up heavy rocks, get them up to chest level and then do a squat-push kinda throw with them. Use the legs to generate force combined with a two-handed chest push. That adds a little type II contraction to my type I hike.

    Get your sprint workout pdf here.

    Stay tuned for Rule #4.

    Mark Fickler

    Mark aka The Old Spartan and Over-50 Fitness Savior is a 64 year old coffee guzzling father of five wandering the outdoors around Albuquerque, New Mexico. Mark helps Active Boomers get lean, healthy and strong so they live rewarding, fun lives using his signature 2 Rule Easy Fat Loss training program.

    {"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}

    Lose Fat, Look Younger, Have More Fun