1. © 2007 McGraw-Hill Higher Education. All rights reserved. Chapter 8: Skeletal Muscle EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6 th edition Scott K. Powers & Edward T. Howley

2. © 2007 McGraw-Hill Higher Education. All rights reserved. Objectives Draw & label the microstructure of skeletal muscle Outline the steps leading to muscle shortening Define the concentric and isometric Discuss: twitch, summation & tetanus Discus the major biochemical and mechanical properties of skeletal muscle fiber types

3. © 2007 McGraw-Hill Higher Education. All rights reserved. Objectives Discuss the relationship between skeletal muscle fibers types and performance List & discuss those factors that regulate the amount of force exerted during muscular contraction Graph the relationship between movement velocity and the amount of force exerted during muscular contraction Discuss structure & function of muscle spindle Describe the function of a Golgi tendon organ

4. © 2007 McGraw-Hill Higher Education. All rights reserved. Skeletal Muscle Human body contains over 400 skeletal muscles –40-50% of total body weight Functions of skeletal muscle –Force production for locomotion and breathing –Force production for postural support –Heat production during cold stress

5. © 2007 McGraw-Hill Higher Education. All rights reserved. Connective Tissue Covering Skeletal Muscle Epimysium –Surrounds entire muscle Perimysium –Surrounds bundles of muscle fibers Fascicles Endomysium –Surrounds individual muscle fibers

6. © 2007 McGraw-Hill Higher Education. All rights reserved. Connective Tissue Covering Skeletal Muscle Fig 8.1

7. © 2007 McGraw-Hill Higher Education. All rights reserved. Microstructure of Skeletal Muscle Sarcolemma: Muscle cell membrane Myofibrils Threadlike strands within muscle fibers –Actin (thin filament) –Myosin (thick filament) –Sarcomere Z-line, M-line, H-zone, A-band & I-band

8. © 2007 McGraw-Hill Higher Education. All rights reserved. Microstructure of Skeletal Muscle Fig 8.2

9. © 2007 McGraw-Hill Higher Education. All rights reserved. Microstructure of Skeletal Muscle Within the sarcoplasm –Sarcoplasmic reticulum Storage sites for calcium –Transverse tubules –Terminal cisternae –Mitochondria

10. © 2007 McGraw-Hill Higher Education. All rights reserved. Within the Sarcoplasm Fig 8.3

11. © 2007 McGraw-Hill Higher Education. All rights reserved. The Neuromuscular Junction Where motor neuron meets the muscle fiber Motor end plate: pocket formed around motor neuron by sarcolemma Neuromuscular cleft: short gap Ach is released from the motor neuron –Causes an end-plate potential (EPP) Depolarization of muscle fiber

12. © 2007 McGraw-Hill Higher Education. All rights reserved. Neuromuscular Junction Fig 8.4

13. © 2007 McGraw-Hill Higher Education. All rights reserved. Muscular Contraction The sliding filament model –Muscle shortening occurs due to the movement of the actin filament over the myosin filament –Formation of cross-bridges between actin and myosin filaments “Power stroke” 1 power stroke only shorten muscle 1% –Reduction in the distance between Z-lines of the sarcomere

14. © 2007 McGraw-Hill Higher Education. All rights reserved. The Sliding Filament Model Fig 8.5

15. © 2007 McGraw-Hill Higher Education. All rights reserved. Actin & Myosin Relationship Actin –Actin-binding site –Troponin with calcium binding site –Tropomyosin Myosin –Myosin head –Myosin tais

16. © 2007 McGraw-Hill Higher Education. All rights reserved. Actin & Myosin Relationship Fig 8.6

17. © 2007 McGraw-Hill Higher Education. All rights reserved. Energy for Muscle Contraction ATP is required for muscle contraction –Myosin ATPase breaks down ATP as fiber contracts Sources of ATP –Phosphocreatine (PC) –Glycolysis –Oxidative phosphorylation

18. © 2007 McGraw-Hill Higher Education. All rights reserved. Sources of ATP for Muscle Contraction Fig 8.7

19. © 2007 McGraw-Hill Higher Education. All rights reserved. Excitation-Contraction Coupling Depolarization of motor end plate (excitation) is coupled to muscular contraction –Nerve impulse travels down T-tubules and causes release of Ca ++ from SR –Ca ++ binds to troponin and causes position change in tropomyosin, exposing active sites on actin –Permits strong binding state between actin and myosin and contraction occurs

20. © 2007 McGraw-Hill Higher Education. All rights reserved. Excitation- Contraction Coupling Fig 8.9

21. © 2007 McGraw-Hill Higher Education. All rights reserved. Steps Leading to Muscular Contraction Fig 8.10

22. © 2007 McGraw-Hill Higher Education. All rights reserved. Properties of Muscle Fiber Types Biochemical properties –Oxidative capacity –Type of ATPase Contractile properties –Maximal force production –Speed of contraction –Muscle fiber efficiency

23. © 2007 McGraw-Hill Higher Education. All rights reserved. Individual Fiber Types Fast fibers Type IIx fibers –Fast-twitch fibers –Fast-glycolytic fibers Type IIa fibers –Intermediate fibers –Fast-oxidative glycolytic fibers Slow fibers Type I fibers –Slow-twitch fibers –Slow-oxidative fibers

24. © 2007 McGraw-Hill Higher Education. All rights reserved. Muscle Fiber Types Fast FibersSlow fibers CharacteristicType IIxType IIaType I Number of mitochondriaLowHigh/modHigh Resistance to fatigueLowHigh/modHigh Predominant energy systemAnaerobicCombinationAerobic ATPaseHighestHighLow V max (speed of shortening)HighestIntermediateLow EfficiencyLowModerateHigh Specific tensionHigh HighModerate

25. © 2007 McGraw-Hill Higher Education. All rights reserved. Comparison of Maximal Shortening Velocities Between Fiber Types Type IIx Fig 8.11

26. © 2007 McGraw-Hill Higher Education. All rights reserved. Histochemical Staining of Fiber Type Type IIa Type IIx Type I Fig 8.12

27. © 2007 McGraw-Hill Higher Education. All rights reserved. Fiber Typing Gel electrophoresis: myosin isoforms –different weight move different distances Table 10.2 + _ Type I Type IIA Type IIx 1 1 – Marker 2 2 – Soleus 3 3 – Gastroc 4 4 – Quads 5 5 - Biceps

28. © 2007 McGraw-Hill Higher Education. All rights reserved. Fiber Typing Immunohistochemical: –Four serial slices of muscle tissue –antibody attach to certain myosin isoforms

29. © 2007 McGraw-Hill Higher Education. All rights reserved. Muscle Tissue: Rat Diaphragm Type 2x fibers - light/white antibody: BF-35 Type 2a fibers - dark antibody: SC-71 Type 2b fiber - dark Antibody: BF-F3 Type 1 fibers - dark antibody: BA-D5

30. © 2007 McGraw-Hill Higher Education. All rights reserved. Fiber Types and Performance Power athletes –Sprinters –Possess high percentage of fast fibers Endurance athletes –Distance runners –Have high percentage of slow fibers Others –Weight lifters and nonathletes –Have about 50% slow and 50% fast fibers

31. © 2007 McGraw-Hill Higher Education. All rights reserved. Alteration of Fiber Type by Training Endurance and resistance training –Cannot change fast fibers to slow fibers –Can result in shift from Type IIx to IIa fibers Toward more oxidative properties

32. © 2007 McGraw-Hill Higher Education. All rights reserved. Training-Induced Changes in Muscle Fiber Type Fig 8.13

33. © 2007 McGraw-Hill Higher Education. All rights reserved. Age-Related Changes in Skeletal Muscle Aging is associated with a loss of muscle mass –Rate increases after 50 years of age Regular exercise training can improve strength and endurance –Cannot completely eliminate the age- related loss in muscle mass

34. © 2007 McGraw-Hill Higher Education. All rights reserved. Types of Muscle Contraction Isometric –Muscle exerts force without changing length –Pulling against immovable object –Postural muscles Isotonic (dynamic) –Concentric Muscle shortens during force production –Eccentric Muscle produces force but length increases

35. © 2007 McGraw-Hill Higher Education. All rights reserved. Isotonic and Isometric Contractions Fig 8.14

36. © 2007 McGraw-Hill Higher Education. All rights reserved. Speed of Muscle Contraction and Relaxation Muscle twitch –Contraction as the result of a single stimulus –Latent period Lasting only ~5 ms –Contraction Tension is developed 40 ms –Relaxation 50 ms

37. © 2007 McGraw-Hill Higher Education. All rights reserved. Muscle Twitch Fig 8.15

38. © 2007 McGraw-Hill Higher Education. All rights reserved. Force Regulation in Muscle Types and number of motor units recruited –More motor units = greater force –Fast motor units = greater force –Increasing stimulus strength recruits more & faster/stronger motor units Initial muscle length –“Ideal” length for force generation Nature of the motor units neural stimulation –Frequency of stimulation Simple twitch, summation, and tetanus

39. © 2007 McGraw-Hill Higher Education. All rights reserved. Relationship Between Stimulus Frequency and Force Generation Fig 8.16

40. © 2007 McGraw-Hill Higher Education. All rights reserved. Length- Tension Relationship Fig 8.17

41. © 2007 McGraw-Hill Higher Education. All rights reserved. Simple Twitch, Summation, and Tetanus Fig 8.18

42. © 2007 McGraw-Hill Higher Education. All rights reserved. Force-Velocity Relationship At any absolute force the speed of movement is greater in muscle with higher percent of fast-twitch fibers The maximum velocity of shortening is greatest at the lowest force –True for both slow and fast-twitch fibers

43. © 2007 McGraw-Hill Higher Education. All rights reserved. Force-Velocity Relationship Fig 8.19

44. © 2007 McGraw-Hill Higher Education. All rights reserved. Force-Power Relationship At any given velocity of movement the power generated is greater in a muscle with a higher percent of fast-twitch fibers The peak power increases with velocity up to movement speed of 200-300 degreessecond -1 –Force decreases with increasing movement speed beyond this velocity

45. © 2007 McGraw-Hill Higher Education. All rights reserved. Force-Power Relationship At any given velocity of movement the power generated is greater in a muscle with a higher percent of fast-twitch fibers The peak power increases with velocity up to movement speed of 200-300 degrees/sec –Force decreases with increasing movement speed beyond this velocity

46. © 2007 McGraw-Hill Higher Education. All rights reserved. Force-Power Relationship Fig 8.20

47. © 2007 McGraw-Hill Higher Education. All rights reserved. Receptors in Muscle Muscle spindle –Changes in muscle length –Rate of change in muscle length –Intrafusal fiber contains actin & myosin, and therefore has the ability to shorten –Gamma motor neuron stimulate muscle spindle to shorten Stretch reflex –Stretch on muscle causes reflex contraction

48. © 2007 McGraw-Hill Higher Education. All rights reserved. Muscle Spindle Fig 8.21

49. © 2007 McGraw-Hill Higher Education. All rights reserved. Receptors in Muscle Golgi tendon organ (GTO) –Monitor tension developed in muscle –Prevents damage during excessive force generation Stimulation results in reflex relaxation of muscle

50. © 2007 McGraw-Hill Higher Education. All rights reserved. Golgi Tendon Organ Fig 8.22

51. © 2007 McGraw-Hill Higher Education. All rights reserved. Chapter 8: Skeletal Muscle