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.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
References in periodicals archive ?
Type II fibers, called fast twitch muscle fibers, can emit maximum contractility in contrast to Type I fibers, but they are easily fatigued.
In contrast, the type II fibers are the fast twitch fibers which have a dependence on glycolytic metabolism.
Although we can still build type I muscles as we age, our type II fibers decline naturally.
On the other hand, white fibers are known as type II fibers. They are characterized by the predominance of the anaerobic pathway, a smaller number of mitochondria, and a higher rate of contraction.
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%).
There are large differences between type I and type II fibers regarding their speed of contraction, oxidative capacity and fatigue resistance.
This discrepancy in the responses of muscle weight and fiber CSA in both muscles might be explained by the differences of contractile properties of muscle fiber types since peak force of slow Type I fibers is lower than that of fast Type II fibers. However, there have been no basic experiments, such as experiments using animal models, investigating a long-term study on the effects of ACL resection on morphological and functional characteristics of skeletal muscles around knee joint.
In addition, it was found that testosterone increases type II fibers, [19] which are the fast fibers with high glycolytic enzyme activity.
[41] found that the relative percentage of type I fibers increased with ageing and the fiber atrophy was most pronounced for type II fibers. As mentioned above, type I fibers were stiffer than type II fibers when generating equal active force.
(12) describe the higher percentage of type II fibers, as it was found in the present work; however, McKeran et al.
(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.