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Muscle Physiology

Muscle Physiology. Chapter 1 cont…. Muscle Fiber Types. Type I- slow twitch muscle fibers ( small ) Fatigue resistant High number of mitochondria High levels of aerobic enzymes Dense capillarization. Type II- fast twitch Type IIa- fast oxidative glycolytic (FOG) ( large )

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Muscle Physiology

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  1. Muscle Physiology Chapter 1 cont…

  2. Muscle Fiber Types • Type I- slow twitch muscle fibers (small) • Fatigue resistant • High number of mitochondria • High levels of aerobic enzymes • Dense capillarization

  3. Type II- fast twitch Type IIa- fast oxidative glycolytic (FOG) (large) Some oxidative characteristics More mitochondria, greater capillarization, and greater aerobic enzyme content than IIx

  4. Type II- fast twitch Type IIx- fast glycolytic (FT) (large) Fatigues rapidly Low numbers of mitochondria Low aerobic enzyme activity

  5. Muscle Fiber Types ST INT FT • Type I Type IIaType IIb • SO FOG FT • Red White • Contraction speed, fatigue rate, diameter, anaerobic enzymes, mitochondrial density, aerobic enzymes, capillarization.

  6. TYPE IIA Type I Fast-Twitch Type IIB(IIX) Slow-Twitch Oxidative Fast-Twitch Oxidative Glycolytic Glycolytic CHARACTERISTIC (SO) (FOG) (FG) Contraction Speed slow fast fast Fatigue rate slow intermediate fast Diameter small intermediate large ATPase low high high Mitochondrial high high low concentration Glycolytic enzyme low intermediate high concentration Characteristics of Skeletal Muscle

  7. KEY POINT • With training, type IIx muscle fibers may be converted to type IIA muscle fibers

  8. Muscle Actions • Concentric- tension developed in the muscle overcomes the resistance causing shortening • Isometric- tension developed in the muscle equals the resistance resulting in no change in length of the muscle • Eccentric- tension developed in the muscle is less than the resistance causing a lengthening of the muscle

  9. Force Productionin Muscle • Motor unit recruitment- • Increased number of motor units recruited • Increased frequency of stimulation of a motor unit increases calcium release causing more crossbridge attachments • Preloading- developing high tension in the muscle isometrically

  10. Cross-sectional area (CSA)- muscles with a greater cross-sectional area have a greater potential for force development (sarcomeres in parallel) Velocity of shortening- longer muscles have a greater potential for velocity of shortening (sarcomeres in series) Therefore, force production is inversely related to velocity

  11. Series vs. Parallel

  12. Cycle Time • Why do graphs look that way? • Rope pulling.

  13. Angle of pennation- Sarcomeres in series, greater speed of movement and range of motion Unipennate and bipennate- sarcomeres parallel, greater potential for developing tension Sarcomere and muscle length- the length-tension relationship of muscle states there is an ideal length for muscle to exert maximal force (resting length or slightly greater than resting length)

  14. Three Arrangements of Muscle Fibers

  15. Prestretching- using the stretch-shortening cycle to prestretch muscle will increase the potential for force production Delayed onset muscle soreness (DOMS)- muscle soreness 24-72 hours post exercise causing a decrease in force production capabilities of muscle

  16. KEY POINT • DOMS is more likely to occur with eccentric exercise • DOMS is related to the deceleration phase of movement and muscle damage

  17. Aging- skeletal muscle decreases in size and strength (sarcopenia) with aging (primarily type ll) Muscle fiber type- fast twitch muscle fibers are capable of faster and stronger muscle actions, but fatigue more rapidly and are less efficient at producing and using ATP

  18. Next Class • Download Moritani and deVries article and write a one page synopsis. • Neuromuscular Chapter 2

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