Muscle Anatomy 101 Pt2

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Muscle Anatomy 101 Pt2

  1. 1. Muscle Anatomy 101 Part II
  2. 2. Muscle Contraction <ul><li>Huxley Sliding Filament Theory </li></ul><ul><li>Briefly- actin slides over myosin causing the z-lines to pull together; thus shortening the sarcomere </li></ul>
  3. 3. <ul><li>Action potential travels to neuromuscular junction </li></ul><ul><li>Acetylcholine (Ach) is released </li></ul><ul><li>Sarcolema is depolarized </li></ul><ul><li>Muscle fiber is excited </li></ul><ul><li>Ca++ is released from sarcoplasmic reticulum </li></ul><ul><li>Ca++ binds to troponin </li></ul><ul><li>Myosin heads bind to actin </li></ul><ul><li>Powerstroke occurs </li></ul><ul><li>ATP binds to crossbridge </li></ul><ul><li>Myosin detaches from actin </li></ul><ul><li>If Ca++ and ATP are present cycle occurs again if physically possible </li></ul>
  4. 4. Muscle Contraction <ul><li>Relaxation occurs when stimulus stops </li></ul><ul><li>Ca++ is actively pumped back into SR </li></ul><ul><li>ATP is required for excitation and relaxation </li></ul>
  5. 5. Size Principle <ul><li>“Motor units are recruited from the smallest to the largest based on the force demands placed on the muscle.” </li></ul><ul><li>Smaller (lower threshold) units are recruited first (predominately Type I) </li></ul><ul><li>Based on force demands larger (higher threshold) units are recruited (predominately Type II) </li></ul>
  6. 6. Size Principle <ul><li>*Important Training Concept* </li></ul><ul><li>Low resistance = smaller units = 12-15RM </li></ul><ul><li>High resistance = larger units = 1-5RM </li></ul><ul><li>*Only recruited units benefit from training* </li></ul>
  7. 7. All-or-None Law <ul><li>“When a specific motor unit reaches its threshold level for action, all of the muscle fibers in that motor unit are activated fully.” </li></ul><ul><li>-Refers to individual unit NOT entire muscle </li></ul><ul><li>-Variation of force </li></ul>
  8. 8. Muscle Activation & Training <ul><li>Different loads recruit different types and numbers of motor units </li></ul><ul><li>Heavier loads recruit more units </li></ul><ul><li>Exception to size principle: High velocity movements </li></ul>
  9. 9. Muscle Activation & Training <ul><li>Recruiting low threshold first delays muscular fatigue for submax exercise </li></ul><ul><li>Neurons of high threshold units ability to recover quickly allows them to be activated quicker in repeated actions </li></ul>
  10. 10. Muscle Activation & Training <ul><li>-To achieve training effect of Type II there must be high power output demands </li></ul><ul><li>-Recruitment order is generally fixed, may change due to body position </li></ul><ul><li>-exercising at various angles? </li></ul>
  11. 11. Muscle Actions <ul><li>Concentric: active shortening (m. force > resistance) </li></ul><ul><li>Eccentric: lengthening (m. force<resistance) </li></ul><ul><li>Isometric: static (m. force=resistance) </li></ul>
  12. 12. Muscle Actions <ul><li>Ascending Curve: force gets greater throughout ROM </li></ul><ul><li>Descending Curve: force greatest at beginning </li></ul><ul><li>Bell Curve: force greatest in middle </li></ul>
  13. 13. Length-Tension (Force) Curve <ul><li>Optimal length at which muscle can generate force </li></ul><ul><li>Optimal length: maximal crossbridge interaction </li></ul>
  14. 14. Force Velocity Curve <ul><li>“As the velocity of muscular movement increases, the force a muscle is able to develop concentrically decreases” </li></ul><ul><li>-The greater the force the slower the movement (concentrically) </li></ul><ul><li>*Opposite true for eccentric muscle actions </li></ul>
  15. 15. Force Velocity Curve <ul><li>High force development is related to tissue damage </li></ul><ul><li>-Muscle soreness after eccentric exercise </li></ul>
  16. 16. Questions?

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