Muscles glycogen from

Structural differences, mainly associated with the average chain lengths, have been reported for two piscine muscle glycogens from Catla catla and Clarias batrachus. ... 

Figure 6. Glycogen content in the vastus lateralis muscle as a function of cycling time at 75-80% of maximal oxygen uptake (VO2 max). Data points are mean values from 10 subjects. For each subject, exercise was performed repeatedly in periods of 15 min separated by 15 min rest periods. At the point of exhaustion and muscle fatigue, muscle glycogen stores were depleted. From Bergstrom and Hultman (1967) with permission from the publisher.

Figure 7. Muscle glycogen utilization rates at various exercise intensities expressed as a percentage of VO2 max. VL, vastus lateralis SOL, soleus CAST, gastrocnemius. Redrawn from Costill etal.(1971), Hermansen etal. (1967), Saltin and Karlsson (1971), and Sherman et al. (1981).

There is, however, one major disadvantage to the continued combustion of CHO and specifically when the source is muscle glycogen. The capacity for energy production from CHO is finite and much less than from fat (Table 1). Continued... 

Figure 8. A. Glycogen content in the vastus lateralis muscle after a mixed diet (a) and during 5 days of total starvation ( ) in one subject and eight days of carbohydrate-poor diet (o) followed by a carbohydrate-rich diet ( ) in a second subject. B. Muscle glycogen content before and after exercise. Before exercise the diet was mixed (a) and in the following days was either total starvation ( ) or carbohydrate-poor (o) and finally followed by 1-2 days of a carbohydrate-rich diet ( ). Note the slow rate of glycogen resynthesis when the diet is carbohydrate-poor compared to the rate when the diet is carbohydrate-rich. Redrawn from Hultman and Bergstrom (1967).

Figure 9. One-legged exercise studies showing the muscle glycogen content of the exercised (—) and rested legs (—) in two subjects. A. Muscle biopsy samples were obtained immediately after exercise (a) and during three days when fed a carbohydrate-rich diet (a). B and C. The diet was total starvation (z) for two days following exercise (B) or carbohydrate-poor (o) for three days following exercise (C). This was followed by a second one-leg exercise bout (T) and a carbohydrate-rich diet ). Redrawn from Bergstrom and Hultman (1966) in panel A, and from Hultman and Bergstrom (1967) in panels B and C.

Figure 10. The relationship between the initial glycogen content in vastus lateralis muscle and work time in six subjects who cycled to exhaustion at 75% VO2 max. Each subject cycled to exhaustion on three occasions. The first experiment was preceded by a mixed diet (a), the second by a carbohydrate-poor diet (o), and the third by a carbohydrate-rich diet ( ). The energy contents of the diets were identical. In all experiments depletion of the muscle glycogen store coincided with exhaustion and muscle fatigue. From Bergstrom et al. (1967) with permission from the publisher.

Skeletal muscle utilizes glucose as a fuel, forming both lactate and CO2. It stores glycogen as a fuel for its use in muscular contraction and synthesizes muscle protein from plasma amino acids. Muscle accounts for approximately 50% of body mass and consequently represents a considerable store of protein that can be drawn upon to supply amino acids for gluconeogenesis in starvation. 

The ATP required as the constant energy source for the contraction-relaxation cycle of muscle can be generated (1) by glycolysis, using blood glucose or muscle glycogen, (2) by oxidative phosphorylation, (3) from creatine... 

Glucose derived from muscle glycogen and metabolized by anaerobic glycolysis is the major fuel source. Blood glucose and free fatty acids are the major fuel sources. 

From the earliest measurements of tissue calcium, it was clear that total calcium is largely a measure of stored calcium. Through the years, scientists have used a variety of indirect measures of [Ca2+]j. These include shortening of or tension in muscles secretion from secretory cells the activity of Ca2+-dependent enzymes, most notably glycogen phosphorylase and flux of K+, or K+ currents, as a reflection of Ca2+-activated K+ channels. In addition, investigators often use the radioactive calcium ion [45Ca2+] as an indirect indicator of Ca2+ concentrations and Ca2+ movements. 

Spectrometer can measure the amount of glycogen from the content of C-labelled glucose in glycogen in Uver or muscle of a volunteer (for description of isotopes, see Appendix 2.2). This is a non-invasive technique, but it gives similar results to the biopsy method (Chapter 16) (Appendix 2.3). 

Figure 6.19 Regulation of the synthesis of glycogen from glucose in liver and muscle. Insulin is the major factor stimulating glycogen synthesis in muscle it increases glucose transport into the muscle and the activity of glycogen synthase, activity which is also activated by glucose 6-phosphate but inhibited by glycogen. The latter represents a feedback mechanism and the former a feedforward. The mechanism by which glycogen inhibits the activity is not known. The mechanism for the insulin effect is discussed in Chapter 12.

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