Why Different Muscle Fibers Is The Secret Behind Strength Or Endurance?

marathoner vs sprinter

What are Different Muscle Fibers?


fast twitch and slow twitch



Muscle Fiber is defined as a fiber inside the muscles, which is responsible for the gaining size & strength, with an endurance level too.

Different Muscle Fibers are responsible for achieving different goals for a human body.

Sometimes we want an explosive power & strength & sometimes we don’t want.

Nature has designed our body, in a very smart way.

Average Body consists of 50 % strength or white muscle fibers & 50 % endurance or red muscle fibers.

We can increase the amount of any of the muscle fibers, depending on our training type & goals.

The muscle fibers are different for strength as compare to endurance.

There are 2 types of muscle fibers:-

1) Fast Twitch Muscle Fibers –  Speed, Power, Size & Strength.

2) Slow Twitch Muscle Fibers –  Endurance.



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Slow Twitch Muscle Fibers are red in color, which is responsible for endurance.

These are the muscle fibers which works on a concept of Sarcoplasmic Hypertrophy.

They are really important for us on a day to day life like walking, cycling, cardio & picking up light objects.

Examples: Marathoners focus only on slow twitch, Bodybuilders focus more on fast twitch as compare to slow one.


Factors Responsible For Slow Twitch Muscle Fibers


  • INTENSITY LEVEL – It is always between 0 % to 50 % of 1 repetition maximum.


  • SIZE – Don’t increase in size.


  • COLOR – Red.



  • GOAL – To increase the endurance level & time under tension


  • REPETITIONS – More than 14 to an infinite number of reps/set.


  • SETS – Only one at a time.

  • REST PERIOD –  not necessary.


  • RECOVERY TIME – Maximum up to 24 hours.


  • TIME UNDER TENSION – Always more than 60 seconds.


  • FUEL TYPE –  Takes Oxygen, Fat & Glucose,  present outside the cell as an energy source.


  • TIME FOR ACTIVATION – It takes more time to activate, as the fuel is present outside the cell.


  • WASTE PRODUCT –  Carbon-di-Oxide by breathing out.



  • More endurance capacity.
  • Burns excessive amount of fat.
  • Burnt Sugar.
  • Improves Cardiovascular Health.
  • Active for a longer duration.



  • Doesn’t increase in size.
  • Lack of power & speed.
  • Takes time to activate.
  • Depends on the external source of energy outside the cell.








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Fast Twitch Muscle Fibers are white in color, which is responsible for power & strength movements.

These are the muscle fibers which works on a concept of Myofibrillar Hypertrophy.

These are really important for us if we want huge power or explosion in the shortest amount of time.

Examples: Footballers, Basketball, Sprinters, Powerlifters, Boxers.

They are further classified into 2 types:-

  • TYPE 2 A – Produces more endurance but slightly less strength.


  • TYPE 2 B – Creates more strength but slightly less endurance.


Factors Responsible For Fast Twitch Muscle Fibers


  • INTENSITY LEVEL – It is always between 60 % to 100 % of 1 repetition maximum.


  • SIZE – Increase in size as the intensity is increased.


  • COLOR – White.



  • GOAL – To create speed, power & strength.


  • REPETITIONS – 1 – 6 reps / set.


  • SETS – 3- 8 sets.

  • REST PERIOD – 2 – 5 min.


  • RECOVERY TIME – At least 48 hours.


  • TIME UNDER TENSION – 30 to 60 seconds maximum.


  • FUEL TYPE –  ATP ( Adenosine triphosphate ) or Glycogen,  present inside the cell.


  • TIME FOR ACTIVATION – It takes less to activate, as the fuel is present inside the cell.


  • WASTE PRODUCT – Lactic Acid burns outside the cell.



  • More power & strength.
  • Explosiveness.
  • Builds Muscle & Size.
  • Boosts the Central Nervous System.
  • Increase the Muscular Contraction.



  • Active for Less duration.
  • Fatigue very easily.
  • Less Time under Tension.
  • More Rest period & Recovery Time.
  • Always have a spotter around you.








  • 0 – 50 % INTENSITY RANGE –  More than 14 repetitions to unlimited, Focus on only Slow Twitch Muscle Fibres.


  • 60 % INTENSITY RANGE –  Around 14 repetitions, target maximum on Slow Twitch Muscle Fibres,  but fast twitch muscle fibers started to activate at this point, which varies from person to person.


  • 75 % INTENSITY RANGE – Around 10 repetitions. Both Slow & Fast Twitch Muscle Fibres equally involve.


  • 85 % INTENSITY RANGE – Around 6 repetitions, only on Fast Twitch Muscle Fibres.


  • 100 % INTENSITY RANGE –  Exact 1 repetition maximum ( Highest muscle potential ), only on Fast Twitch Muscle Fibres.


(Note: Fast Twitch Muscle Fibres activate at different percentages in every individual, like on 58,59 or 60,61,62 % on some people, so 60 % is just an average approximation, it varies on different people based on their genetics, that’s why it can’t be 50 or 70 % which will create a much different, around 60 % will be the best option.)




Choose any compound exercise, like a bench press, deadlift, squats, etc.

Pick up a weight according to your 1 rep max ( 100 % intensity level ).

Suppose your 1 rep max is 100 pounds, then pick up 80 pounds, which is 80 % of your 1 rep max.

This information will help every athlete, whether he is a beginner, intermediate or advance to measure the level of their performance & start building goals to break their current limit.

Start doing reps & calculate the number of fibers on the following results, as shown below:


  • 1 Repetition Maximum- Only For Powerlifting, Only Fast Twitch Muscle Fibres.


  • 1 – 5 Repetitions Range- Advanced Athletes, Fast Twitch Muscle Fibres ( Strength Lifters Range).


  • 6 – 10 Repetitions Range- Intermediate Athletes, Slow & Fast Twitch Muscle Fibres ( Bodybuilding Range ).


  • 10 – 14 Repetitions Range- Beginner Athletes, Slow Twitch Muscle Fibres ( Warm Up Range ).


  • More than 14 Repetitions-  Cardio Type Workout, Only Slow Twitch Muscle Fibres ( Marathoner Range ).




Finally, I hope you must be got the details of the importance of muscle fiber.

Remember one thing, muscle hypertrophy, muscle fibers, body type & nutrition all matters, when you want to build a good physique.

If any one of the point you become unaware of then you will gain nothing.

You should know which muscle fiber you really want to target.

Are you focussing on power and speed or endurance level to burn fat?

Slow Twitch & Fast Twitch muscle fibers both are really important in our life.

Someday we have to fight or fly, so both of the muscles are equally important.

Both of them have their benefits & importance.

So next time when you hit the gym, make sure to train the right type of muscle fibers, based on your goals.

Check this link, for more information,

Slow & Fast Twitch Muscle Fibers





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