1. Skeletal Muscle: Structure and Function
Chapter 18
Skeletal Muscle: Structure and Function
Copyright © 2007 Lippincott Williams & Wilkins.
McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

2. Gross Structure of Skeletal Muscle
Fiber: a muscle cell
Long
Slender
Multinucleated
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

3. Levels of Organization
Connective tissue layers
Endomysium: wraps each fiber
Perimysium: surrounds several fibers and forms bundles called fasciculi
Epimysium: surrounds all the bundles to form the entire muscle
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5. Tendons: tissue connecting muscle to periosteum of bone
Origin: more stable bone
Insertion: moving bone
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

6. Sarcolemma: muscle cell membrane
Satellite cells: myogenic stem cells located within the sarcolemma
Help regenerative cell growth
Play a role in hypertrophy
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

7. Sarcoplasmic reticulum
Extensive latticelike network of tubules and vesicles
Provides structural integrity
Stores, releases, and reabsorbs Ca2+
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8. Chemical Composition 75% water 20% protein
5% salts, phosphates, ions, macronutrients
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

9. Blood Supply Skeletal muscle has a rich vascular network.
Flow is rhythmic
Vessels compress during contraction phase.
Vessels open during relaxation phase.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

10. Capillarization Training increases capillary-to-muscle fiber ratio.
Expedites removal of heat and metabolic byproducts
Increases delivery of O2, nutrients, and hormones
Copyright © 2007 Lippincott Williams & Wilkins.
McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

11. Skeletal Muscle Ultrastructure
Fibrils contain myofilaments.
Actin
Myosin
Also of functional importance
Troponin
Tropomyosin
In addition, there are several other structural proteins.
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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13. The Sarcomere Runs from Z line to Z line
Is the functional unit of a muscle fiber
Copyright © 2007 Lippincott Williams & Wilkins.
McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

14. Muscle Fiber Alignment
Long axis of a muscle
From origin to insertion
Determines fiber arrangement
Fusiform
Pennate
Bipennate
Fiber arrangement influences
Force-generating capacity
Physiologic cross sections
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

15. Actin–Myosin Orientation
Actin filaments lie in a hexagonal pattern around myosin.
Crossbridges spiral around the myosin where actin and myosin overlap.
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17. Actin–Myosin Orientation
Tropomyosin: lies along actin in the groove formed by the double helix
Inhibits actin–myosin interaction
Troponin: embedded at regular intervals along actin
Interacts with Ca2+
Moves tropomyosin, uncovering active actin sites
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

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19. Intracellular Tubule Systems
The T tubular system is distributed around the myofibrils such that each sarcomere has 2 triads.
Each triad contains
2 vesicles
1 T tubule
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21. Chemical and Mechanical Events During Muscle Action and Relaxation
Sliding-filament model
Contraction occurs as myosin and actin slide past one another.
Myosin crossbridges cyclically attach, rotate, and detach from actin filaments.
Energy is provided by ATP hydrolysis.
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23. Mechanical Action of Crossbridges
Myosin crossbridges contain actin-activated ATPase.
Provide mechanical power strokes
Perform repeated, nonsynchronous strokes
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

24. Link Between Actin, Myosin, and ATP
Myosin head bends around ATP molecule, becomes cocked
Myosin interacts with actin.
ATP is hydrolyzed.
Energy release forces power stroke.
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27. Excitation–Contraction Coupling
Psychologic mechanism
Electrical discharge at muscle initiates chemical events at cell surface.
Cell releases Ca2+.
Muscle action results.
Copyright © 2007 Lippincott Williams & Wilkins.
McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

28. Relaxation Ca2+ is actively pumped into SR.
Troponin allows tropomyosin to interfere with actin–myosin interaction.
Copyright © 2007 Lippincott Williams & Wilkins.
McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

29. Muscle Fiber Type
Two distinct fiber types identified by characteristics:
Contractile
Metabolic
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

30. Fast-Twitch Fibers: Type II
High capacity to transmit AP
High myosin ATPase activity
Rapid Ca2+ release and uptake by SR
High rate of crossbridge turnover
Capable of high force generation
Rely on anaerobic metabolism
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31. Slow-Twitch Fibers: Type I
Low myosin ATPase activity
Slower Ca2+ release and uptake by SR
Low glycolytic capacity
Large and numerous of mitochondria
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

32. Fast-Twitch Subdivisions
IIa fibers
Fast shortening speed
Moderately well-developed capacity for both anaerobic and aerobic energy production
IIb fibers
Most rapid shortening velocity
Rely on anaerobic energy production
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

33. Species Differences Metabolic scope Contractile dynamics
Force and power
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McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition

34. Fiber Type Differences among Athletic Groups
Large individual difference in fiber type distribution
Endurance athletes > Type I fibers
Some as high as 90 – 95% in gastrocnemius
Speed and power athletes > Type II fibers
Middle-distance athletes have a more even fiber distribution.
Copyright © 2007 Lippincott Williams & Wilkins.
McArdle, Katch, and Katch: Exercise Physiology: Energy, Nutrition, and Human Performance, Sixth Edition