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Energy for skeletal muscle contraction
ATP sources The many causes of muscle fatigue Classification of skeletal muscle fiber types
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ATP and muscle contraction
Need ATP for Cross-bridge formation, power stroke (myosin ATPase) Ca++ transport to SR (Ca++ ATPase) Na+/K+ transport across sarcolemma (Na+/K+ ATPase)
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Sources of ATP ATP pool Phosphocreatine.
At rest, ATP phosphorylates creatine. During exercise, creatine kinase (creatine phosphokinase) moves phosphate from phosphocreatine to ATP
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Sources of ATP Glucose (glycolysis) to pyruvate citric acid cycle oxidative phosphorylation (about 30 ATP per glucose molecules) Anaerobic glycolysis: glucose lactic acid (2 ATP per glucose molecule)
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Sources of ATP Beta oxidation of fatty acids. Fatty acids are converted to acetyl CoA citric acid cycle in the mitochondria, need oxygen Slow During light exercise
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Sources of ATP glucose catabolism during heavy exercise
carbo loading builds up glycogen stores Protein catabolism during starvation
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Fatigue Muscle is no longer able to generate sustained expected power output A variety of contributing factors depends on the degree of muscle activity
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Fatigue: contributing factors
Intensity of muscle activity Duration of muscle activity Aerobic/anaerobic metabolism Muscle composition Fitness level Ions Nutrients Neurotransmitter
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Fatigue during extended submaximal exertion
Not ATP shortage Glycogen depletion may affect Ca++ release from SR
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Fatigue during short duration maximal exertion
Lots of inorganic phosphate from ATP hydrolysis may slow P release from myosin:ADP:Pi slows power stroke Acidosis may inhibit some enzymes
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More factors for muscle fatigue
K+ : intracellular K+ lowered during repetitive action potentials affects Ca++ release channels on SR membrane Acetyl choline depletion at the myoneural junction low end-plate potential (disease)
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More factors for muscle fatigue
CNS: Subjective feelings preceding physiological fatigue Acidosis may influence perception of fatigue
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