Creatine phosphate during exercise

Two major types of muscle fibers are found in humans white (anaerobic) and red (aerobic). The former are particularly used in sprints and the latter in prolonged aerobic exercise. During a sprint, muscle uses creatine phosphate and glycolysis as energy sources in the marathon, oxidation of fatty acids is of major importance during the later phases. Nonmuscle cells perform various types of mechanical work carried out by the structures constituting the cytoskeleton. These strucmres include actin filaments (microfilaments), micrombules (composed primarily of a- mbulin and p-mbulin), and intermediate filaments. The latter include keratins, vimentin-like proteins, neurofilaments, and lamins. 

During the recovery period from exercise, ATP (newly produced by way of oxidative phosphorylation) is needed to replace the creatine phosphate reserves — a process that may be completed within a few minutes. Next, the lactic acid produced during glycolysis must be metabolized. In the muscle, lactic acid is converted into pyruvic acid, some of which is then used as a substrate in the oxidative phosphorylation pathway to produce ATP. The remainder of the pyruvic acid is converted into glucose in the liver that is then stored in the form of glycogen in the liver and skeletal muscles. These later metabolic processes require several hours for completion. 

During periods of recovery following exercise, creatine phosphate is regenerated at the expense of ATP synthesized from mitochondrial oxidative phosphorylation energy currency is paid into a reserve account, or reservoir, for the next period of sustained exercise. 

Under standard conditions, this reaction would be unfavourable but physiological conditions during recovery phase after exercise are such as to allow creatine phosphate formation to occur. 

Figure 14.7. Sources of ATP During Exercise. In the initial seconds, exercise is powered by existing high phosphoryl transfer compounds (ATP and creatine phosphate). Subsequently, the ATP must be regenerated by metabolic pathways.

The different fuels used by exercising muscle are discussed in subsequent sections. These fuels may be arranged in the following "hierarchy," where the order of appearance approximates relative importance during exercise (1) creatine phosphate, (2) muscle and liver glycogen, (3) gluconeogenesis, and (4) fatty acids. 

Creatine phosphate serves as a small reservoir of high-energy phosphate that can readily regenerate ATP from ADR As a result, it plays a particularly important role in muscle during exercise. It also carries high-energy phosphate from... 

EXAMPLE 13.30 Creatine phosphate concentration in the cytoplasm of skeletal muscle is 15 mM. Since the rate of ATP consumption during intense exercise is 3 mmol L s , there is potentially a 5 s supply of creatine phosphate. Many sprinters and power lifters attempt to increase the amount of creatine phosphate in their muscles by ingesting creatine as a dietary supplement. There is strong evidence to suggest that this strategy is effective, but the long-term effects on general health, particularly kidney function, are yet to be determined. 

Furthermore, P NMR studies can be used to follow therapeutic interventions. As a rule, a fast decline in creatine phosphate content during exercise, no synthesis of phospho-monoesters, and a delayed creatine phosphate resynthesis after exercise are found in patients with a mitochondrial disorder. 

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