Muscle Fibers - Type IIB

Description

Type IIB Muscle Fibers are a sub-type of Type II Muscle Fibers that have a greater ability to split Adenosine Triphosphate (ATP).  They are “fast twitch” and have a low concentration of Myoglobin accounting for their white physical appearance.  They contain large quantities of Glycogen and produce ATP by metabolism.  They fatigue rapidly but provide fast and forceful contractions.  These Muscle Fibers are only given a signal to fire if a maximum Muscle contraction is required.  Type IIb Muscle Fibers react to weight training by developing larger Myofilaments (i.e. they are the type of Muscle Fiber that is most involved in Muscle Growth).  It is Type IIB Muscle Fibers that body-builders seek to enlarge.