fast-twitch fibers

(redirected from Type II fibers)

fast-twitch fi·bers

(fast-twich fī'bĕrz)
Histologically distinct skeletal muscle fibers that generate energy rapidly and are active in quick, powerful actions; subclassified as types IIa and IIb.
Synonym(s): fast glycolytic (FG) fibers, fast-oxidative-glycolytic (FOG) fibers, Type II fibers.
References in periodicals archive ?
In ATPase staining, two patients (40%) had an even distribution of Type I and Type II fibers, while Type II fibers were dominant in two patients (40%) and Type I fibers were dominant in one patient (20%).
9,10) Hypothyroidism is associated with change in muscle fiber type from fast twitch type II to slow twitch type I and alteration of oxidative muscle enzyme activity with decreased calcium ATPase activity of fast twitch type II fibers leading to delayed relaxation.
1987) reported that in lambs fed cimaterol the proportion of type I to type II fibers in the longissimus and semitendinosus muscle were unaffected.
This difference could be related to the decreased variability among type II fibers (which predominate in fast muscles) than among fibers of types I and II (both of which are present in slow muscles).
This could be attributed to the common factors affecting type I and type II fibers, such as, reduced ATP production due to the reduced substrate availability, accumulation of metabolic end products that impair contractile events, changes in intracellular and extracellular muscle electrolyte concentration that reduce muscle excitability, and alterations in sarcoplasmic reticulum calcium handling properties23.
Most studies on rat skeletal muscle have indicated that more GLUT4 is present in the type I fibers compared with the type II fibers (5,15,23).
In human, where the MyHC2b is hardly expressed in type II fibers, a long-term AAS administration (power lifters taking anabolic supplements for nearly 10 years) increased the CSA of type I and type II fibers both in m.
Type I fibers use aerobic metabolism, making type I fibers more important in endurance activities whereas type II fibers use anaerobic metabolism, making type II fibers more important for sprint and power athletes.
Strength relies on the presence of larger, more numerous type II fibers.
People whose muscles were affected by polio use both type I and type II fibers for ordinary walking.
In addition, age is characterized by a lower level of myocytes and reduction in the transversal area of the fibers, especially type II fibers (Song et al.