White muscle fibers

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. 

Zebrafish larvae possess two types of skeletal muscle fibers. Slow (red) muscle fibers, a superficial monolayer on the siuface of the myotome, are equipped for oxidative phosphorylation, can generate relatively large stores of energy, and are most resistant to fatigue. Fast (white) muscle fibers, in the deep portion of the myotome, are least resistant to fatigue because they rely on anaerobic glycolysis for... 

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

Typically, these elevations occur in all three fiber types, but they are most pronounced in red muscle, least in white muscle. Whereas the total amount of power that a muscle can gen-... 

Figure 18.4 The Cori cycle. Glucose is metabolized anaerobically to lactate, as in white muscle fibers or red blood cells. Lactate is exported into the bloodstream, extracted from there by the liver, and reconverted to glucose via gluconeogenesis. Glucose is then returned to the muscle.

Phosphorylation by ADP, catalyzed by adenylate kinase - this enzyme is especially important in the rapid synthesis and turnover of thiamin triphosphate in slow-twitch white muscle fibers. 

Skeletal muscles are organized into extrafusal and intrafusal fibers. Extrafusal fibers are the strong, outer layers of muscle. This type of muscle fiber is the most common. Intrafusal fibers, which make up the central region of the muscle, are weaker than extrafusal fibers. Skeletal muscles fibers are additionally characterized as fast or slow based on their activity patterns. Fast, also called white, muscle fibers contract rapidly, have poor blood supply, operate anaerobically, and fatigue rapidly. Slow, also called red, muscle fibers contract more slowly, have better blood supplies, operate aerobically, and do not fatigue as easily. Slow muscle fibers are used in movements that are sustained, such as maintaining posture. 

Skeletal muscle is composed of two different types of cells white and red muscle fibers. Some muscles are fairly homogeneous and contain mainly one type of fiber others contain mixtures of both types. White muscle fibers contain relatively few mitochondria, are mainly glycolytic, and produce lactic acid as an end-product of fermentation- Red muscle fibers are relatively rich in mitochondria and are well adapted to oxidising fatty adds and glucose to CO2- Their energy metabolism is dependent on an ample supply of oxygen. 

If you were a long-marathon runner, would you expect to have more highly developed white muscle fibers or red muscle fibers Hint Consult 1-igure 4.31. (Also sfw Collnick and Hodgson, 19fWi.)... 

While fat, 383, 411, 556 White muscle fibers, 233 WiC program, 758 WLLsun s disease, 817-818... 

The developmental aspects of the differentiation of fiber types has been studied by a number of workers. It has become clear that at an early age all or most muscles tend to resemble more closely red muscles, both in their speed of contraction and in their metabolic pattern. Bass and coworkers (B5) have recently detailed the developmental changes in glycolytic and oxidative enzymes in red and white muscle in the chicken their results illustrate the much greater changes which occur in white muscle. 

Fig. 2. Transverse section of fish white muscle showing bChn s (1940) primary fibers. Adductor superficialis of Leuciscus rulilus L. Magnification 700 X (after BUHN, 1940).

Mitochondrial abnormalities, in the form of SDH-hyperactive, COX-negative fibers, also increase with age in rat muscles, but the alterations in this species correlate with the type of muscle and probably depend in large measure on fiber type composition in the vastus lateralis, composed predominantly of type 2 fibers, SDH-hyperintensive, COX-negative fibers were detected at 18 months of age whereas in the soleus muscle, which is richer in type 1 fibers, the same alterations were noted at 36 months of age [8]. As mentioned above, in humans the greater vulnerability of type 2 fibers to sarcopenia is also present but masked by the more admixed fiber type composition, such that we do not have obviously "red" or "white" muscles. 

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