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I've been running on and off for the past 12 years, having originally started in high school with XC. Given that fact, I've typically always been interested in running longer distances, however, within the past year or so, I've shifted my focus to sprinting.

From what I currently understand about the matter, sprinters prefer having a high ratio of fast-twitch muscle fibers. What I would like to know, or at least get some idea of, is what kind of fast/slow-twitch muscle fiber ratio my legs contain (without going to the hospital and requesting a biopsy, if that's even possible).

Upon searching YouTube, I wasn't really able to find any videos that demonstrate how to get an assessment of this ratio, other than this video, however, the guy is testing his chest, and, IMO, his test doesn't seem to be designed very well.

That being said, is there a way to at least somewhat accurately test the fast/slow-twitch muscle fiber ratio, specifically in your legs?

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  • Muscle biopsies are possible. There is also some evidence that some fiber types can change as well.
    – JohnP
    Aug 29 '17 at 21:23
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    ncbi.nlm.nih.gov/pmc/articles/PMC3131401 from 6ish years ago, but you'd need access to a good physiologist or research university willing to do it on and individual basis.
    – JohnP
    Aug 29 '17 at 21:26
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Accurately no. Unfortunately there are no proven ways to measure muscle fiber composition.

A muscle biopsy is an invasive technique involving the surgical removal of a small muscle tissue sample. This procedure is done to diagnose muscle tissue diseases when less invasive tests are not available. This is not a method used to determine whole muscle fiber composition.


Muscle Fiber Types

Skeletal muscle fibers can be classified into three types:

  • Type I: Slow oxidative fibers
  • Type IIa: Fast oxidative fibers
  • Type IIx: Fast glycolytic fibers

  • Most muscles contain mixture of fiber types, resulting in a range of contractile speed and fatigue resistance

  • All fibers in one motor unit are the same type

  • Genetics dictate individual’s percentage of each

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Training Effects on Muscle Fiber Type

Aerobic (Endurance) Exercise Such as jogging, swimming, biking leads to increased:

  • Muscle capillaries
  • Number of mitochondria
  • Myoglobin synthesis
  • Results in greater endurance, strength, and resistance to fatigue
  • May convert fast glycolytic fibers into fast oxidative fibers

Resistance Exercise (Anaerobic), Such as weight lifting or isometric exercises, leads to increased

  • Mitochondria
  • Myofilaments
  • Glycogen stores
  • Connective tissue
  • Muscle strength and Size (hypertrophy)
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  • What is the source of this table/info?
    – Enivid
    Aug 31 '17 at 18:51
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    -1. Muscle biopsies can be used to determine composition, and have been used many times in clinical kinesiology.
    – JohnP
    Aug 31 '17 at 19:26
  • Also you have been warned about copy/paste without attribution (i.e. plagiarism) before. Please give the correct attribution.
    – JohnP
    Aug 31 '17 at 19:30
  • "Muscle biopsies can be used to determine composition, and have been used many times in clinical kinesiology." Where are your sources? How would you like me to cite a PowerPoint?
    – Mike-DHSc
    Aug 31 '17 at 23:11
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    If you have a source, even if it is a power point, I would expect you to cite where you got the power point. In this case, I found your entire answer in a SUNY biology course sample presentation. As far as sources, it's common knowledge in the kinesiology field. Here is a paper from 1972 describing using muscle biopsy to determine fiber types. exercisephysiology.net/articles/… .
    – JohnP
    Sep 1 '17 at 4:34

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