Type II muscle fiber

Type II muscle fibers (white muscle, fast muscle) (Table 6) contribute to rapid muscle contraction by using energy obtained from stored ATP, and ATP production from creatine phosphate and anaerobic glycolysis of glycogen. However, the myoglobin content of these fibers is low [144,145], which may lead to less marked increases in serum myoglobin and creatine phosphokinase (CPK) in patients with ALPE. 

Does ALPE develop via the release of a renal vasoconstricting substance by type II muscle fibers ... 

The following issues, including the etiology, remain to be clarified (a) the pathogenesis of ALPE, (b) the prevention of relapse, and future exercise guidance, (c) why delayed CT shows patchy contrast enhancement even in the recovery phase, (d) whether or not patchy renal vasoconstriction persists for 1-2 weeks, (e) why a contrast medium is present in the kidney for 72 h maximum, (f) the association between ALPE and disorders of type II muscle fibers, (g) the reasons for the less marked increases in serum myoglobin and creatine phosphokinase (CPK), and (h) why ALPE frequently develops in patients with renal hypouricemia. 

EXAMPLE 13.21 Type II muscle fibers are subdivided into type Ila and type Ilb. Type Ila can use both aerobic and anaerobic metabolism to produce ATP whereas type lib fibers use only anaerobic metabolism. In contrast to type I muscle fibers, type lib fibers contract rapidly after stimulation by a nerve impulse. They have evolved for short-lived, powerful contractions by the possession of characteristically active myosin ATPases and a dense packing of contractile filaments. So much of the cytoplasmic space is taken up with filaments that little exists for mitochondria. Similarly, these fibers are associated with a relatively poor blood supply. Type lib fibers are also known as white and fast-twitch muscle fibers and are adapted for short-lived but powerful contractions. The relative paucity of mitochondria and the poor blood supply impose obvious constraints on the generation of ATP during exercise. 

Type of muscle fiber Type I Red muscle Aerobic exercise Type II White muscle Anaerobic exercise... 

Fiber type. Skeletal muscle has several distinct fiber types. Type I is used primarily for aerobic activity, whereas type II is specialized for short, intense bursts of activity. How could you distinguish between these types of muscle fiber if you viewed them with an electron microscope ... 

These are postulated as adversely influencing mainly the type-2 fibers (or sub-preferentially the type-2B fibers). Hypothetically, "pan-denervations" are due to (a) abnormality of both type-2 and type-1 LMNs or of their intimately related, respectively type-2 and type-1 Schwann cells (which are nurturing the LMNs and being nurtured by them). This results in lack of trophic influence on "all" the muscle fibers, either (i) fully (in pan-denervations) or (ii) partially deficient - quantitatively or qualitatively - (in pan-dysinnervations), to which the type-2 muscle fibers (or sub-preferentially type-2B fibers) are more susceptible or (b) hypothetically, relatively selective abnormality at the level of the presumed type-2 LMNs, or of their closely associated Schwann cells that we designate as "type-2 (or type-2B) Schwann... 

Figure 3. Top panel Whole muscle force (x) and single fiber PCr (a, a) and ATP ( , ) concentrations at rest and after 10 and 20 sec of intermittent electrical stimulation at 50 Hz. Open symbols denote type I fibers closed symbols denote type II fibers. Bottom panel Glycogenolytic rates in type I and II fibers during the 20 sec stimulation period. The open bar denotes type I fibers the closed bar denotes type II fibers.

Some researchers reject the explanation that caffeine inhibits glycogen depletion during short term exercise54 but there is an increasing abundance of research supporting the notion of variable sensitivity to caffeine by muscle type. Muscles with higher ratios of type I fibers appear more sensitive than type II fibers, both in animal55-56 and human models.57... 

Smooth muscle differs from skeletal muscle in various ways. Smooth muscles—which are found, for example, in blood vessel walls and in the walls of the intestines—do not contain any muscle fibers. In smooth-muscle cells, which are usually spindle-shaped, the contractile proteins are arranged in a less regular pattern than in striated muscle. Contraction in this type of muscle is usually not stimulated by nerve impulses, but occurs in a largely spontaneous way. Ca (in the form of Ca -calmodulin see p.386) also activates contraction in smooth muscle in this case, however, it does not affect troponin, but activates a protein kinase that phosphorylates the light chains in myosin and thereby increases myosin s ATPase activity. Hormones such as epinephrine and angiotensin II (see p. 330) are able to influence vascular tonicity in this way, for example. 

I realize that this is a side track issue, but relevant all the same. Cycle protocols were an approach intended to facilitate optimal growth of muscle tissue. Remember there are two main muscle fiber types Type I, which is endurance orientated, and Type II which is strength orientated. Type "Ha", "Hb", and Type "He" are responsible for most musculature size and have the greatest potential for growth. Testosterone increases the number of Type II fibers at the expense of the Type I transformation. Growth hormone, Insulin, IGF-1, and thyroid hormones effect growth and hyperplasia of both fiber types. This should be another key relating to protocols that were utilized and why. 

Mammalian skeletal muscle can be separated Into two distinct fiber populations, based on relative contraction characteristics, and are referred to as slow-twltch (Type I) or fast-twitch (Type II) fibers. The slow-twltch fiber type exhibits a relatively low shortening velocity (27), a low rate of tension development (27). a low myosin ATPase activity (28) and a low rate of calcium sequestration by the sarcoplasmic reticulum (29). The converse Is true for the fast-twitch fibers. Since contraction velocity highly correlates with myosin ATPase activity (30), It Is possible to easily Identify,... 

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