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Fast Twitch vs Slow Twitch Muscle Fiber Training


Strength vs. Endurance Training

On today’s episode of Live Lean TV, I’m answering an interesting question about fast twitch vs slow twitch muscle fiber training.

I received this question from my Instagram, so click here to follow me and ask questions over there as well.

The question went something like this:

I used to train for strength, but I got bored, so I switched to marathon training. I’ve run my marathon, but I now notice I’ve lost strength. So I’m now back in the gym lifting weights. My problem is I notice I’m getting stronger in my upper body, but I’m not able to lift as much as I used too with my legs. What’s the deal? Did my marathon training ruin my leg strength?

I hear this from a lot of different people

Essentially someone starts lifting weights, then they switch to endurance training.


After they run a few marathons, they change their training goal to rebuild lost strength.

They notice the strength builds back up in their upper body, but they’re confused as to why their leg strength is not growing as fast.

Well this all comes down to your body’s muscle fibers.

Fast Twitch vs Slow Twitch Muscle Fiber Training

Muscle fibers can be broken down into two different types:

  • Fast twitch muscle fibers
  • Slow twitch muscle fibers

What are slow twitch muscle fibers?

Fast Twitch vs Slow Twitch Muscle Fiber Training Live Lean TV

Slow twitch muscle fibers fire slower, so they are not as explosive, but they can go for longer periods of time before fatiguing. 

These slow twitch muscle fibers are mainly used for endurance training.

This means a marathon runner would use more slow twitch muscle fibers.

What are fast twitch muscle fibers?

Fast Twitch vs Slow Twitch Muscle Fiber Training Live Lean TV

Fast twitch fibers, on the other hand, generate short bursts of speed and strength, but fatigue much quicker.

Sprinters and weight lifters would use more of these ballistic, fast twitch muscle fibers.

So as you can tell, the muscle fiber type you possess can influence which activities you’re good at. 

How do you know which muscle fibers you have more of?

If you’re better at endurance sports, such as long distance running, your body probably possesses more slow twitch fibers. 

If you can run fast for short periods of time, and jump high, your body probably possesses more fast twitch muscle fibers.

What is your training goal?

When it comes to training, think about your fitness goal is.

Is it endurance based like running a marathon?

Or is it to get stronger, faster, and more explosive for a specific sport.

Whatever your goal is, your training needs to be focused on using those specific motor units and muscle fibers. 

Let’s get back to the original question

Why did this person quickly gain strength back in his upper body, but is having problems gaining strength back in his legs?

Well there is evidence showing that specific long-term endurance training can make fast twitch muscle fibers take on the properties of slow twitch muscle fibers in your legs.

Since you’ve been training for a marathon, the fast twitch muscle fibers in your legs may have taken on the properties of slow twitch muscle fibers, thus you’re not able fire the leg muscles to lift as much.

Fortunately, the conversion of muscle fiber types is not permanent.

Within 6 months of continued strength training, you should be able to fire up those fast twitch muscle fibers and hit new personal bests with your legs.

Thanks for the question. 

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47 responses to “Fast Twitch vs Slow Twitch Muscle Fiber Training

  1. I doubt one can change one type of muscle to another type, one muscle type
    might be more dominant than another .but like apples and oranges ,each are
    its own.

  2. hey brad do you have any idea how one can let his fast twitch muscles adopt the properties of the slow twitch muscle intentionally ??

  3. If you really desire to get shredded, you may want to Google the term “SSM Muscle Method”. You are guaranteed to get the muscles you want.

  4. My coworkers laughed when I told them I would bulk up with Morsch Muscle Madness, but then they saw the results. Google Morsch Muscle Madness to see their reaction.

  5. Have you heard about Cosmos Fat Loss? (check it out on google) It is a quick and easy way to lose weight fast.

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  8. This must explain why I can walk 4 MPH for 2 or 3 miles (depends if I do weights or not) no problem but can’t seem to pull more than 20-25 lbs of weights with the ankle strap on my ankle. I’d actually love to run but my knees are shot. When I ran just 4 miles several times a week for exercise years ago, I had the best lower body.

  9. My classmates laughed when I told them I was going to bulk up with “H6x Muscle Monster”, but then I showed them the results. Google H6x Muscle Monster to see their reaction.

  10. BRAD…. I’ve just come across Spirulina …. have you heard of it before> Ihave trouble getting protein in unless through meat and fish, which I dont always want and this has a lot of protein…. YAY OR NAY???

  11. So Brad, is there specific exercises to do that can help speed up the return of Fast twitch muscle fiber?
    Also should you alternate between these exercises and more slow twitch exercises?

    I have followed a Hypertrophy specific training schedule for a while and it cycled through endurance to hypertrophy every 6 weeks or so. here’s the web site that I got the program from

    keep up the good work!

  12. hey brad thanks for some wonderful videos…one question i am recovering from a bad case of viral fever was out of action fro last three months..started working out from about a month now…how should i go about it..i see that i am recovering but i am feeling bloatness at times…

  13. Brad can u make a video on does your digestive system have to do with fat loss because I notice that all of a sudden I can’t poop the same anymore and I gained more fat since than, Idk what’s wrong with me

  14. So, what is better for fat loss? Fast or slow twitch fibres? Combo of both?
    Is it purely dependent what your goals are to what muscle fibres you focus on building?

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