UWL BIO 312 - Skeletal muscle (2 pages)

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Skeletal muscle

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Skeletal muscle


Lecture notes on muscle fatigue and the adaptations the body makes to fatigue.

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Lecture Note
University of Wisconsin-La Crosse
Bio 312 - Human Anatomy and Physiology I
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Bio 312 Lecture 22 Lecture Outline 1 Muscle Fiber types 2 Muscle fatigue a Synaptic fatigue b Conduction fatigue c Lactic acid buildup 3 Endurance training adaptations 4 Resistance training adaptations a CNS adaptations with resistance training Fiber 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 each o The higher proportion of slow twitch muscle a person has the faster they can consume oxygen o Genetics is the biggest factor for fiber type distribution o Characteristics of motor neuron can play a role in determining muscle fiber type o All muscle fibers within a given motor unit are the same fiber type Muscle 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 junction o Motor neuron being stimulated for long periods of time causes axon to run out of synaptic vesicles to push neurotransmitter into synaptic cleft o Can be shown in lab but not thought to be major factor for muscle fatigue in environment Conduction fatigue occurs in transverse tubules of sarcolemma o After extended periods of use action potentials do not penetrate all the way into the transverse tubules and do not stimulate deeper parts of muscle o 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 activities o 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 training Increased myoglobin oxygen binding protein that pulls O2 into mitochondria Occurs only in muscles being trained o Increased oxidative capacity via more mitochondria more krebs cycle and ETC enzymes o Increased quantity of stored glycogen in muscle and improved ability to metabolize it o 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 acid o Increased capillary density in trained muscle leads to better diffusion of O2 and nutrients o Increased cardiac output increased stroke volume lowered resting heart rate and sub max exercise HR Resistance training adapations changes in body caused by resistance training o Increased stores of ATP creatine phosphate myosin ATPase ad creatine kinase o 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 cells o 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 size o Ergogenic aids to improve performance Nutritional supplements Dihydroepiandrosterone DHEA anabolic effects protein building when it is converted to testosterone o

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