twitch athlete

[Bapopik at AOL.COM]

Athletes have "fast twitch" fibers.
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_http://en.wikipedia.org/wiki/Skeletal_muscle_
(http://en.wikipedia.org/wiki/Skeletal_muscle)
Red and white fibers
Skeletal muscles contain two main types of fibers, which differ in the
mechanism they use to produce ATP; the amount of each type of fibre varies from
muscle to muscle and from person to person.
    *   Red ("slow-twitch") fibers have more _mitochondria_
(http://en.wikipedia.org/wiki/Mitochondria) , store _oxygen_
(http://en.wikipedia.org/wiki/Oxygen)  in _myoglobin_ (http://en.wikipedia.org/wiki/Myoglobin) ,  rely on
_aerobic metabolism_ (http://en.wikipedia.org/wiki/Aerobic_metabolism) ,  have a
greater _capillary_ (http://en.wikipedia.org/wiki/Capillary)  to volume ratio
and are associated with _endurance_ (http://en.wikipedia.org/wiki/Endurance) ;
these produce ATP  more slowly. _Marathon runners_
(http://en.wikipedia.org/wiki/Marathon_(sport))   tend to have more red fibers, generally through a
combination of genetics and  training.
    *   White ("fast-twitch") fibers have fewer mitochondria, are capable of
more  powerful (but shorter) contractions, metabolize ATP more quickly, have a
lower  capillary to volume ratio, and are more likely to accumulate _lactic
acid_ (http://en.wikipedia.org/wiki/Lactic_acid) . _Weightlifters_
(http://en.wikipedia.org/wiki/Weightlifting)  and _sprinters_
(http://en.wikipedia.org/wiki/Sprinting)   tend to have more white fibers.
Fast fibers come in three varieties, called type IIa, IIx and IIb. Type IIx
fibers in people used to be called, confusingly, type IIB. Type IIb fibers
predominate in the fast muscle of small mammals that have to accelerate their
limbs very fast against little load. Human type IIx (aka IIB) are our fastest
fibers. Type IIc fibers are the slowest of all of them, and have only 36 units
 of myocin.
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