fast twitch and slow twitch muscle

Discussion in 'Strength & Conditioning Discussion' started by Vilo Magee, Jan 23, 2006.

  1. Vilo Magee

    Vilo Magee Brown Belt Professional Fighter

    Nov 9, 2004
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    done with this place
    Dunno who wrote this but it is a good little article

    Fast and Slow Twitch Muscle Fibers.

    How they affect your performance:
    It is generally accepted that there are two basic types of muscle fibers. Slow twitch (Type I) muscle and fast twitch (Type II) muscle fiber. Research is currently looking at the specific makeup of these fibers and the 'fast' and 'slow' categories are much simplified. It appears that the fast twitch fibers can be further categorized into Type IIa and Type IIb fibers (1)(2).

    Until further evidence is available however, these distinctions will help us discuss and understand how muscle fibers affect performance.

    Human muscles contain a genetically determined mixture of both slow and fast fiber type. On average, we have about 50% slow and 50% fast fibers in most of the muscles used for movement. The slow muscles contain more mitochondria and myoglobin which make them more efficient at using oxygen to generate ATP without lactate acid build up. In this way, the slow twitch fibers can fuel repeated and extended muscle contractions such as those required for endurance events like a marathon.

    The two fiber types generally produce the same amount of force per contraction, but fast twitch fibers produce that force at a higher rate (they fire more rapidly). So a lot of fast twitch fibers can be an asset to a sprinter when there is a limited amount of time to generate maximal force. The slow twitch fibers, on the other hand, fire less rapidly, but can go for a long time before they fatigue.

    Fiber Type and Performance

    The genetic component of muscle fiber type can not be overlooked when it comes to performance. Olympic athletes tend to be genetically blessed with large variations in fast and slow twitch fibers that perfectly suit their sport. Olympic sprinters have been shown to possess about 80% fast twitch fibers while those who excel in the marathon may have 80% slow twitch fibers.

    Can you change your muscle fiber type by training?

    This is a hard question to answer because good studies are just now being conducted (3). Currently, there is limited evidence to show that human skeletal muscle switches fiber types from "fast" to "slow" due to training (4). Researchers have demonstrated a fast-to-slow fiber transformation in animal skeletal muscle, and the human studies are showing similar outcomes. There is decent evidence that pure fast (Type IIb) fibers can transition to "hybrid" (Type IIa) fibers with chronic endurance training.

    What can I do to improve my performance?

    Keep in mind that genetic differences may be dramatic at the elite levels of athletic competition, but for the typical athlete, following the principles of conditioning will dramatically improve personal performance.

    Following the principle of overload is the cornerstone of training. With consistent endurance training muscle fibers can develop more mitochondria and surrounding capillaries. In this way training improves your muscle's ability to cope with and adapt to the stress of exercise.

    Fiber type alone is a poor predictor of performance, even among elite endurance athletes. There are many other factors that go into determining athletic success, including mental preparedness, proper nutrition and hydration, getting enough rest, and having appropriate equipment and conditioning.


    (1) McArdle, W.D., Katch, F.I. & Katch,V.L. (1996). Exercise physiology : Energy, nutrition and human performance (4th ed.). Philadelphia : Lea & Febiger
    (2) Lieber, R.L. (1992). Skeletal muscle structure and function : Implications for rehabilitation and sports medicine. Baltimore : Williams & Wilkins.
    (2) Andersen, JL; Schjerling, P; Saltin, B. Muscle, Genes and Athletic Performance. Scientific American. 9/2000
    (3) Thayer R, Collins J, Noble EG, Taylor AW. A decade of aerobic endurance training: histological evidence for fibre type transformation. J Sports Med Phys Fitness. 2000 Dec;40(4).
  2. ACR4V3N

    ACR4V3N Blue Belt

    Nov 29, 2005
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    South Jersy shore
    Good info. I posted a thread on this asking about them with the idea of punching and such.
  3. OpethDrums

    OpethDrums Banned Banned

    Jan 8, 2005
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    Brown Belt
    i have always wondered if squatting every day for 1 week, for example, would tear down the muscle more and make it stronger in the end. your body will adapt to it.. but say you squat 1 day. you tear down the muscle a little but there are still fibers that didnt really get worked. that didnt get torn. if you squat 2 days in a row there will be more stress on the fibers that didnt get used the day before right? wonder if really tearing down your mucsle by working it hard every day will make you stronger in the end than taking rest days. im curious because i go to a boxing gym every day and do a similar leg workout every day
    (a lot of stairs and jumping) and my legs are stronger, recover faster, don't get tired like they did before when i would squat twice a week. i do have a fast metabolism and i get gains really fast if i eat right. do y0u think someone with a fast metabolism that eats a lot but is skinny gets better results from day in day out stress on the muscles? is this the secret to old man strength? as opposed to work rest work rest.
  4. rugger 05

    rugger 05 White Belt

    Jan 18, 2006
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    good question Opeth... all the research I have read supports the notion of rest to build back the muscle fibers... we have all seen 'old man strength" however and it contiues to perplex me
  5. peanut butter

    peanut butter Blue Belt

    Feb 23, 2005
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    isnt old man strength , strength of the lower arms and hands. also if you work on a certain area a lot, wouldnt your tendons be stronger.
  6. Ian Coe

    Ian Coe Silver Belt Professional Fighter

    May 25, 2003
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    I don't think you can compare squats which in total would comprise say 3 minutes of work to stair running and jumping. One heavily taxes the CNS and muscular fibres, whereas the other taxes the muscular fibres, but not as heavily (due to the time involved you can't tear the fibres as deeply)

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