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Muscle Physiology KINE 4396/5390 Strength and Conditioning Christopher Ray, PhD, ATC, CSCS

Muscle Physiology KINE 4396/5390 Strength and Conditioning Christopher Ray, PhD, ATC, CSCS. Objectives.  Anatomy of Skeletal Muscle.  M uscular contraction.  Muscle Fiber Types/Recruitment.  M uscle action.  Force production.

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Muscle Physiology KINE 4396/5390 Strength and Conditioning Christopher Ray, PhD, ATC, CSCS

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  1. Muscle Physiology KINE 4396/5390 Strength and Conditioning Christopher Ray, PhD, ATC, CSCS

  2. Objectives Anatomy of Skeletal Muscle Muscular contraction MuscleFiber Types/Recruitment Muscle action Force production

  3. Three Types of Connective Tissue:Epimysium, Perimysium, and Endomysium

  4. Three Arrangements of Muscle Fibers Fibers parallel to tendon Bipennate muscle Unipennate muscle

  5. Fiber Pennation • In a pennated muscle not all of the force generated in the muscle fiber is delivered to the tendon. • Pennated muscles usually compensate for this disadvantage by increasing the cross-sectional area. • Pennated muscles do not move a joint through as large of ROM as do unipennate muscles.

  6. A Motor Unit • All muscle fibers of a motor unit contract together • Connects via a neuromuscular junction • Each cell has 1 • Motor Neuron has many

  7. The discharge of an action potential from a motor nerve signals the release of calcium from the sarcoplasmic reticulum into the myofibril, causing tension development in muscle.

  8. Contraction of a Myofibril: Stretched Muscle • I-bands are Actin in two adjacent sarcomeres • A-bands are Myosin • During contraction the H-zone and I-bands decrease.

  9. Contraction of a Myofibril: Partially Contracted Muscle

  10. Contraction of a Myofibril: Completely Contracted Muscle

  11. Contraction of a Myofibril: Stretched Muscle Contraction of a Myofibril: Completely Contracted Muscle H-Zone and I-band shrink

  12. Sliding Filament Mechanism/Theory • Resting Phase • Little Ca++ is present so few X-Bridges attached. • Excitation-Contraction Coupling Phase • Stimulus spreads thru T-Tubule • SR releases Ca++ • Ca++ binds with Troponin exposing bind site on Actin • Myosin binds with Tropomyosin • Contraction Phase • ATP downgraded to ADP + P • Myosin arm does work on actin • Recharge Phase • Pick up new ATP • Myosin head rotates backward • Relaxation Phase • Ca++ is pumped back into SR

  13. Calcium and ATP are necessary for myosin cross-bridge cycling with actin filaments.

  14. Type II, or fast-twitch, muscle fibers are capable of developing higher forces than Type I, or slow-twitch, muscle fibers—especially at higher velocities of muscle action.

  15. The number of cross-bridges that are attached to actin filaments at any instant in time dictates the force production of a muscle.

  16. Force Production & Factors influencing Force • Motor Unit Recruitment • Preloading [holding a wt tightens up the muscles elastic structures]. • Cross-Sectional Area • Increasing the cross-sectional area increases strength • Velocity of Shortening • Angle of Pennation • Sarcomere and Muscle Length • Prestretching (Stretch-Shorten Cycle) • Eccentric contraction followed by an immediate concentric contraction [Plyometrics] • Exercise-Induced Muscle Damage (DOMS) • Older Muscle • Sarcopenia (reduced muscle size & strength with age) • Muscle Fiber Type • Type I (SO) aerobic fiber, low force, slow rise time • Type IIa (INT) anaerobic fiber, high force, shorter rise time • Type IIb (FT) anaerobic fiber, very high force, fastest rise time

  17. Many factors may affect rate of cross-bridge cycling and thus force, including neural activation, calcium concentration, myosin ATPase activity, preloading, prestretch, muscle fiber type and ultrastructure, fatigue through a variety of mechanisms, and number of contractile components (myosin and actin) in parallel.

  18. Improving Force Production • Use preloading during training to develop strength early in ROM. • Accomodating resistance apparatus (hydraulic, isokinetic) do not load the muscle prior to contraction. • Increase cross-sectional area of muscle by using moderate resistance (65-80%) for max or near max # of reps. • When overloading eccentrically use heavy resistance. • When training for explosive concentric use light resistance. • Prestretch a muscle before concentric to enhance force production. • Incorporate rest days into training cycle to avoid training with DOMS and allow muscle time to repair.

  19. Questions • In an attempt to increase his 1 rm bench max; George increased his resistance and added negatives. He complains of increased soreness 48 hrs later. What is the soreness called? What is the cause? • What is occurring • Resistance is greater than muscle force • Resistance and force is equal • Resistance is less than muscle force

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