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  1. 1. Skeletal-Muscle Energy Metabolism<br />
  2. 2. ATP (Adenosine Triphosphate) performs functions directly related to muscle-fiber contraction and relaxation<br /> provides energy for myosin cross-bridge movements<br />allosteric binding of ATP on myosin cross-bridge<br /> provide energy for Ca+ transport<br /> ATP molecules must be produced rapidly to sustain contractile activity<br />
  3. 3. Three ways to form ATP during contractile activity<br />Phosphorylation of ADP by creatine phosphate<br /> Oxidative phosphoryation of ADP in the mitochondria<br /> Substrate-level phosphorylation of ADP by the glycotic pathway in the cytosol<br />
  4. 4. Phosphorylation of ADP by creatine phosphate<br /> - provides a very rapid means of forming ATP at <br /> the onset of contractile activity<br /> - when the bond between creatine and phosphate is <br /> broken, energy is released<br /> - energy can be transferred to ADP to form ATP in <br /> a reversible reaction catalyzed by creatinekinase<br />CP + ADP C + ATP<br />- amount of energy formed is limited by the initial <br /> concentration of creatine phosphate in the cell<br /> - at the start of contractile activity, provides few seconds necessary for oxidative phosphorylation & glycolysis to increase their rates of ATP formation<br />
  5. 5. oxidative phosphorylation of ADP in the mitochondria<br />- produced most of the ATP used for muscle contraction at moderate levels of muscular activity<br /> muscle glycogen<br />The major fuel contributing to oxidative phosphorylation during the first 5 – 10 minutes o exercise<br />Blood glucose & fatty acids<br />Become dominant in the next 30 minutes of the exercise<br /> fatty acids<br />Become more important beyond 30 minutes of the exercise<br />Glycolysis<br />Contributes to the total ATP when the intensity of the exercise exceeds 70% of the maximal rate of ATP breakdown<br />
  6. 6. Glycolytic pathways<br />Can produce large quantities of ATP when enough enzymes and substrates are available in the absence of oxygen<br /> two sources of glucose for glycolysis<br />Blood<br />Stores of glycogen within the contracting muscle fibers <br /> as intensity of muscle activity increases<br />Greater fraction of total ATP production is formed by anaerobic glycolysis<br /> at the end of muscle activity<br />Creatine phosphate & glycogen levels in the muscle decreases<br />
  7. 7. creatine phosphate & glycogen (energy-storing compounds)<br />Must be replaced<br /> Replacement requires energy <br /> elevated consumption of oxygen following an exercise repays oxygen dept – the increased production of ATP by oxidative phosphorylation following exercise that is used to restore the energy reserves in the form of creatine phosphate & glycogen<br />
  8. 8. Muscle fatigue<br /> the decline in muscle tension as a result of previous contractile activity<br /> decreased shortening velocity and a slower rate of relaxation<br /> at the onset, its rate of development depend on<br /> the type of skeletal-muscle fiber that is active <br />on the intensity <br />duration of contractile activity<br />
  9. 9. if a muscle is allowed to rest after the onset of fatigue it can recover its ability to contract upon restimulation<br /> the rate of recovery depends upon<br />The duration and the intensity of the previous activity<br /> types of fatigue<br />High-frequency fatigue<br />Accompanies high-intensity, short duration exercise (ex. Weight lifting)<br /> Low-frequency fatigue<br />Develops more slowly with low-intensity, long duration exercise (ex. Long-distance running<br /> requires much longer periods of rest before the muscles achieves complete recovery<br />
  10. 10. Muscle fatigue have evolved as a mechanism for preventing the onset of rigor<br />High-frequency fatigue occurs primarily because of a failure of the muscle action potential to be conducted into the fiber along the T tubules and thus a failure to release calcium from the sarcomastic reticulum<br />Recovery is rapid with rest<br />No single process can account for the low-frequency fatigue<br />One major factor is the build up of lactic acid<br />Recovery probably requires protein synthesis<br />
  11. 11. Central command fatigue<br />Due to failure of the appropriate regions of the cerebral cortex to send excitatory signals to the motor neurons<br />Causes an individual to stop exercising though the muscle are not fatigue<br />
  12. 12. Types of skeletal-muscle fibers<br />Can be identified based on <br />Maximal velocities<br /><ul><li>Fast fibers
  13. 13. Slow fibers</li></ul>Major pathway used to form ATP<br />Oxidative fibers<br />glycolytic fibers<br />
  14. 14. Fast fibers<br />Fibers containing myosin with high ATPase activity<br /> containing myosin with lower ATPase activity<br />slow fibers<br />
  15. 15. Three types of skeletal-muscle fibers <br />Slow-oxidative fibers (type I)<br />Combine low myosin-ATPase activity with high oxidative capacity<br />Fast-oxidative fibers (type IIa)<br />Combine high myosin-ATPase activity with high oxidative capacity<br />Fast-glycolytic fibers (type IIb)<br />Combine high myosin-ATPase activity with high glycolytic capacity<br />