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UWL BIO 312 - Skeletal muscle

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Lecture 22 Lecture Outline:1. Muscle Fiber types2. Muscle fatiguea. Synaptic fatigueb. Conduction fatiguec. Lactic acid buildup3. Endurance training adaptations4. Resistance training adaptationsa. CNS adaptations with resistance trainingFiber Types: - Skeletal muscle is not homogeneous tissue (not all muscle fibers are identical)- Fiber type distribution:o Highly variable from species to species and within same species o Average active person is about 50% of eacho The higher proportion of slow twitch muscle a person has, the faster they can consume oxygeno Genetics is the biggest factor for fiber type distributiono Characteristics of motor neuron can play a role in determining muscle fiber typeo All muscle fibers within a given motor unit are the same fiber typeMuscle Fatigue: decline in force producing ability as a result of previous contractile activity- Dependent on fiber type, intensity and duration of contractile activity, state of fitness- Muscle fatigue has multiple causes, and varies based on activity- Synaptic fatigue: occurs at neuromuscular junctiono Motor neuron being stimulated for long periods of time causes axon to run out of synaptic vesicles to push neurotransmitter into synaptic clefto Can be shown in lab, but not thought to be major factor for muscle fatigue in environment- Conduction fatigue: occurs in transverse tubules of sarcolemmao After extended periods of use, action potentials do not penetrate all the way into the transverse tubules and do not stimulate deeper parts of muscleo Caused by buildup of K+ blocking AP’s- Lactic Acid Buildup: lactic acid   lactate + H+ o Buildup of H+ in skeletal muscle alters protein conformation and activity Actin and myosin activity decrease Less Ca2+ release from SR Decreases enzymatic activity  less ATP production  Decreased fatty acid mobilization- Buildup of P from ATP  ADP + P slows the reaction, decreasing rate of cycling- Low intensity, long-duration exercise: lactic acid, conduction failure, cross-bridge cycling inhibition do not play major roles in muscle fatigue during these activitieso Depletion of muscle glycogen and low blood sugar play more important roles because of biochemistry of slow twitch muscles- Endurance training adaptations: changes in body caused by aerobic trainingBio 312o Increased myoglobin (oxygen binding protein that pulls O2 into mitochondria) Occurs only in muscles being trainedo Increased oxidative capacity via: more mitochondria, more krebs cycle and ETC enzymeso Increased quantity of stored glycogen in muscle and improved ability to metabolize ito Increased oxidation of fat as fuel for ATP re-supply, related to more enzymes for FFA metabolism, increased FFA mobilization, which can also be stimulated by caffeine and inhibited by lactic acido Increased capillary density in trained muscle leads to better diffusion of O2 and nutrientso Increased cardiac output, increased stroke volume, lowered resting heart rate and sub-max exercise HR- Resistance training adapations: changes in body caused by resistance trainingo Increased stores of ATP, creatine phosphate, myosin ATPase ad creatine kinaseo Increased muscle mass via increased protein synthesis (more actin, myosin, and titin) Hypertrophy theory: existing cells increase in diameter (more myofibrils per sarcolemma)- More accepted theory for increased muscle mass Hyperplasia: increased number of cells in the trained muscle Satellite cells: undifferentiated cells thought to be cause behind both hypertrophy and hyperplasia- Resistance training activates these cells and give rise to immature muscle cellso CNS adaptations: how CNS learns and adapts during resistance training Better able to turn on more motor units simultaneously and stimulate at higher frequency Occurs rapidly early in training, why you notice gains in strength before gains in muscle sizeo Ergogenic aids to improve performance Nutritional supplements: Dihydroepiandrosterone (DHEA) anabolic effects (protein building) when it is converted to


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UWL BIO 312 - Skeletal muscle

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