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Thread: Muscle Fibre Types

  1. #1
    Senior Member Growth's Avatar
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    Jan 2004

    Muscle Fibre Types

    It seems some people on this forums know which fibre types generally make up each much, ie calfs / forearms are mostly type I slow twitch fibres etc. Is there a site which has the approximate ratios for each muscles or does someone out there know the general fibre compositions for each muscle?

  2. #2
    Senior Member geoffgarcia's Avatar
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    May 2002
    Most muscles contain almost an even split of slow (Type I) and fast (Type II) fibers. There are a few exceptions, however, as the soleus muscle of the calf is predominantly slow twitch, while the gastrocnemius muscle and the hamstrings are predominantly fast twitch. Also, individuals that are involved in sports with vastly different requirements, like sprinters vs. marathon runners, may have a higher/lower percentage of one fiber type.
    The quadriceps is a large muscle group composed of the vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris and controls knee extension. The quadriceps is highly active in endurance activities such as cycling (Gollnick et al., 1972) and running (Widrick et al., 1996a) and power activities such as jumping (Häkkinen and Komi, 1986). The vastus lateralis in untrained individuals is characterized by a large proportion of type I fibers (45-59%), a moderate type IIa proportion (30-39%), and a small type IIb proportion (11-15%) (Esbjörnsson et al., 1999; Simoneau and Bouchard, 1989).

    However, there is a wide variation between individuals and type I, type IIa, and type IIb proportions have been observed to range between 15-79%, 13-77%, and 0-44%, respectively (Simoneau and Bouchard, 1989). The vastus medialis and the vastus lateralis contain similar percentages of type I fibers, 52.1% (Gollnick et al, 1972) and 51.4% (Kuzon et al., 1990) respectively.

    However, as many as 79% of the gastrocnemius fibers (Costill et al., 1976b) and 88% of the soleus fibers (Johnson et al, 1972) may have type I characteristics. The high proportion of type I fibers in the quadriceps, gastrocnemius and soleus is probably due to the fact that these are postural and locomotive muscles that are active for a long duration, but at low contractile forces. In contrast, muscles of the upper body, such as the triceps and biceps, are used for brief forceful contractions and composed of high proportions (60-70%) of type II fibers (Johnson et al, 1972; MacDougall et al, 1982; 1984).
    The gastrocnemius and soleus muscles have more Type II (slow-twitch) muscle fibers than some of the other major muscle groups.
    the makeup of these muscles is primarily Type I fibers due to the fact that these gastroc/soleus group is active throughout the day as you walk, go up stairs, or even stand stationary. Therefore to increase their size you must stimulate the Type II-b fibers to hypertrophy
    Last edited by geoffgarcia; 06-17-2004 at 03:24 PM.

  3. #3
    Senior Member
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    Feb 2004
    The gastrocnemius and soleus muscles have more Type II (slow-twitch) muscle fibers than some of the other major muscle groups.

    There seem to be a few contradictions in those quotes. it refers to calf muscles as type 2 (slow twich). Type one is slow twich. Type 2 is split into a and b. Both are fast twich. Type 2b is recurited under maximal load. It also happens to be the one that grows with the most volume response when stimulated.

    Last edited by Augury; 06-17-2004 at 04:02 PM.

  4. #4
    Formerly Nick Hatfield SW's Avatar
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    May 2004
    Type II is awsome!
    Last edited by SW; 06-17-2004 at 08:40 PM.
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