1. Chapter 8: Skeletal Muscle
EXERCISE PHYSIOLOGY
Theory and Application to Fitness and Performance, 5th edition
Scott K. Powers & Edward T. Howley
Presentation revised and updated by
TK Koesterer, Ph.D., ATC
Humboldt State University

2. 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. 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. 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. Connective Tissue Covering Skeletal Muscle
Epimysium
Surrounds entire muscle
Perimysium
Surrounds bundles of muscle fibers
Fascicles
Endomysium
Surrounds individual muscle fibers
Fig 8.1

6. Connective Tissue Covering Skeletal Muscle
Fig 8.1

7. 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
Fig 8.2

8. Microstructure of Skeletal Muscle
Fig 8.2

9. Microstructure of Skeletal Muscle
Within the sarcoplasm
Sarcoplasmic reticulum
Storage sites for calcium
Transverse tubules
Terminal cisternae
Mitochondria
Fig 8.3

10. Within the Sarcoplasm
Fig 8.3

11. 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
Fig 8.4

12. Neuromuscular Junction
Fig 8.4

13. 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
Fig 8.5

14. The Sliding Filament Model
Fig 8.5

15. Actin & Myosin Relationship
Actin-binding site
Troponin with calcium binding site
Tropomyosin
Myosin
Myosin head
Myosin tais
Fig 8.6

16. Actin & Myosin Relationship
Fig 8.6

17. 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
Fig 8.7

18. Sources of ATP for Muscle Contraction
Fig 8.7

19. 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. Excitation-Contraction Coupling
Fig 8.9

21. Steps Leading to Muscular Contraction
Fig 8.10

22. Properties of Muscle Fiber Types
Biochemical properties
Oxidative capacity
Type of ATPase
Contractile properties
Maximal force production
Speed of contraction
Muscle fiber efficiency

23. 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. Muscle Fiber Types Fast Fibers Slow fibers
Characteristic Type IIx Type IIa Type I
Number of mitochondria Low High/mod High
Resistance to fatigue Low High/mod High
Predominant energy system Anaerobic Combination Aerobic
ATPase Highest High Low
Vmax (speed of shortening) Highest Intermediate Low
Efficiency Low Moderate High
Specific tension High High Moderate

25. Comparison of Maximal Shortening Velocities Between Fiber Types
Type IIx
Fig 8.11

26. Histochemical Staining of Fiber Type
Type IIa
Type IIx
Type I
Fig 8.12

27. Fiber Typing + _ Gel electrophoresis: myosin isoforms
different weight move different distances + _ 1
1 – Marker 2
2 – Soleus 3
3 – Gastroc 4
4 – Quads 5
5 - Biceps
Type I
Type IIA
Type IIx
Table 10.2

28. Fiber Typing Immunohistochemical: Four serial slices of muscle tissue
antibody attach to certain myosin isoforms
Table 10.2

29. Muscle Tissue: Rat Diaphragm
Type 1 fibers - dark
antibody: BA-D5
Type 2b fiber - dark
Antibody: BF-F3
Type 2x fibers - light/white
antibody: BF-35
Type 2a fibers - dark
antibody: SC-71

30. 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. 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
Fig 8.13

32. Training-Induced Changes in Muscle Fiber Type
Fig 8.13

33. 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. 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
Fig 8.14

35. Isotonic and Isometric Contractions
Fig 8.14

36. 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
Fig 8.15

37. Muscle Twitch
Fig 8.15

38. 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
Fig 8.16
Fig 8.17
Fig 8.18

39. Relationship Between Stimulus Frequency and Force Generation
Fig 8.16

40. Length-Tension Relationship
Fig 8.17

41. Simple Twitch, Summation, and Tetanus
Fig 8.18

42. 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
Fig 8.19

43. Force-Velocity Relationship
Fig 8.19

44. 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 degrees•second-1
Force decreases with increasing movement speed beyond this velocity

45. 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 degrees/sec
Force decreases with increasing movement speed beyond this velocity
Fig 8.20

46. Force-Power Relationship
Fig 8.20

47. 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
Fig 8.21

48. Muscle Spindle
Fig 8.21

49. 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
Fig 8.22

50. Golgi Tendon Organ
Fig 8.22