Week 2: Lecture 2    Elaine Wilson, PT
<ul><li>Describe concentric, eccentric, and isometric activation of muscle </li></ul><ul><li>Identify the anatomic compone...
<ul><li>Describe the passive length-tension relationship of muscle  </li></ul><ul><li>Explain why the force production of ...
Structure and Function  of Skeletal Muscle
<ul><li>Sole producer of active force in the body </li></ul><ul><li>Stimulated by the nervous system, muscle contracts and...
<ul><li>Concentric (shortening or contracting) </li></ul><ul><ul><li>Muscle produces active force and simultaneously short...
<ul><li>Relative points of muscle to bone attachment  </li></ul><ul><li>Proximal attachment (origin)  </li></ul><ul><ul><l...
<ul><li>Agonist  </li></ul><ul><ul><li>Muscle or muscle group most directly related to performing a specific movement </li...
<ul><li>Co - contraction  </li></ul><ul><ul><li>Occurs when agonist and antagonist muscles are simultaneously activated in...
<ul><li>Force-couple </li></ul><ul><ul><li>Synergistic action occurring when muscles produce force in different linear dir...
<ul><li>Muscle belly </li></ul><ul><ul><li>Muscle body, composed of numerous fasciculi </li></ul></ul><ul><ul><li>Epimysiu...
<ul><li>Muscle fiber </li></ul><ul><ul><li>An individual cell with multiple nuclei; contains all the contractile elements ...
<ul><li>Basic contractile unit of muscle fiber </li></ul><ul><li>Composed of actin and myosin protein filaments </li></ul>...
<ul><li>Created when  myosin filaments containing numerous “heads”attach to thinner actin filaments </li></ul><ul><li>Myos...
<ul><li>Three factors determine functional potential of a muscle: </li></ul><ul><ul><li>Cross-sectional area </li></ul></u...
<ul><li>Thickness of a muscle, an indirect measure of contractile elements available to generate force </li></ul><ul><li>T...
<ul><li>Shape is one important indicator of a muscle’s specific action </li></ul><ul><li>Most muscles are one of four shap...
<ul><li>Fusiform muscles </li></ul><ul><ul><li>Fibers run parallel to one another </li></ul></ul><ul><ul><li>Built to prov...
<ul><li>Rhomboidal muscles </li></ul><ul><ul><li>Expansive proximal and distal attachments  </li></ul></ul><ul><ul><li>Sha...
<ul><li>Resemble shape of a feather   </li></ul><ul><li>Muscle fibers approach a central tendon at an oblique angle  </li>...
<ul><li>Muscle forces can be described as  vectors  because they possess both a direction and a magnitude  </li></ul><ul><...
<ul><li>Degree to which muscle is either stretched or shortened at the time of its activation </li></ul><ul><li>Significan...
<ul><li>Active length-tension relationship </li></ul><ul><ul><li>Force generated by such a process is highly dependent on ...
<ul><li>Passive length-tension relationship </li></ul><ul><ul><li>Because of its elasticity, a muscle also produces force ...
<ul><li>Mono-articular muscles cross one joint; multi-articular muscles cross multiple joints  </li></ul><ul><li>A multi-a...
<ul><li>Velocity of a muscular contraction can significantly affect force production  </li></ul><ul><li>During a concentri...
<ul><li>Isometric activation creates greater force than any speed concentric contraction  </li></ul><ul><li>During an ecce...
<ul><li>Muscle held in a shortened position will shorten; muscle held in an elongated position will lengthen </li></ul><ul...
<ul><li>Overly tight muscle causes associated joints to assume a posture mimicking the muscle’s primary actions—e.g, a tig...
<ul><li>Therapists often increase patients’ muscular strength, employing overload and specificity </li></ul><ul><li>Overlo...
<ul><li>Although ligaments and capsules can stabilize joints, only muscle can  adapt  to the immediate and long-term exter...
<ul><li>Force generated by muscle is the primary means of balancing stable posture and active movement  </li></ul><ul><li>...
<ul><li>Please read Chapter 4 in textbook prior to lecture on Tuesday 01/31/12 </li></ul><ul><li>Quiz #2: Chapters 3 & 4 –...
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chapter 03 week 2 lecture 2

  1. 1. Week 2: Lecture 2 Elaine Wilson, PT
  2. 2.
  3. 3. <ul><li>Describe concentric, eccentric, and isometric activation of muscle </li></ul><ul><li>Identify the anatomic components that comprise a whole muscle </li></ul><ul><li>Describe the sliding filament theory </li></ul><ul><li>Describe how cross-sectional area, line of pull, and shape help determine the functional potential of a muscle </li></ul><ul><li>Describe the active length-tension relationship of muscle </li></ul>
  4. 4. <ul><li>Describe the passive length-tension relationship of muscle </li></ul><ul><li>Explain why the force production of a multi-articular muscle is particularly affected by its operational length </li></ul><ul><li>Describe the principles of stretching muscular tissue </li></ul><ul><li>Describe the basic principles of strengthening muscular tissue </li></ul>
  5. 5. Structure and Function of Skeletal Muscle
  6. 6. <ul><li>Sole producer of active force in the body </li></ul><ul><li>Stimulated by the nervous system, muscle contracts and pulls on bone to create movement </li></ul><ul><li>When a muscle contracts, the freest (or less constrained) segment moves </li></ul>Mosby items and derived items © 2009 by Mosby, Inc., an affiliate of Elsevier Inc.
  7. 7. <ul><li>Concentric (shortening or contracting) </li></ul><ul><ul><li>Muscle produces active force and simultaneously shortens </li></ul></ul><ul><li>Eccentric (attempting to resist elongation) </li></ul><ul><ul><li>Muscle attempts to contract but is pulled to a longer length by a dominant external force </li></ul></ul><ul><li>Isometric (remaining at a constant length) </li></ul><ul><ul><li>Muscle generates active force while remaining at a constant length </li></ul></ul>Mosby items and derived items © 2009 by Mosby, Inc., an affiliate of Elsevier Inc.
  8. 8. <ul><li>Relative points of muscle to bone attachment </li></ul><ul><li>Proximal attachment (origin) </li></ul><ul><ul><li>Point of attachment closest to the midline or “core” of the body in the anatomic position </li></ul></ul><ul><li>Distal attachment (insertion) </li></ul><ul><ul><li>Point of attachment farthest from the midline or body “core” </li></ul></ul>
  9. 9. <ul><li>Agonist </li></ul><ul><ul><li>Muscle or muscle group most directly related to performing a specific movement </li></ul></ul><ul><ul><ul><li>e.g., quadriceps are agonists for knee extension </li></ul></ul></ul><ul><li>Antagonist </li></ul><ul><ul><li>Muscle or muscle group that can oppose the action of the agonist </li></ul></ul><ul><ul><ul><li>e.g., during elbow flexion, biceps are agonists and triceps are antagonists, passively elongating as the elbow is flexed </li></ul></ul></ul>
  10. 10. <ul><li>Co - contraction </li></ul><ul><ul><li>Occurs when agonist and antagonist muscles are simultaneously activated in an isometric fashion </li></ul></ul><ul><li>Stabilizer </li></ul><ul><ul><li>Muscle that “fixes” or holds a body segment relatively stationary so that another muscle can more effectively perform   </li></ul></ul><ul><li>Synergists </li></ul><ul><ul><li>Muscles that work together to perform a particular action </li></ul></ul>
  11. 11. <ul><li>Force-couple </li></ul><ul><ul><li>Synergistic action occurring when muscles produce force in different linear directions but produce torque in the same rotary direction </li></ul></ul><ul><li>Excursion </li></ul><ul><ul><li>Shortening and lengthening of a muscle </li></ul></ul><ul><ul><li>Typically a muscle can only shorten or elongate about half of its resting length </li></ul></ul>
  12. 12. <ul><li>Muscle belly </li></ul><ul><ul><li>Muscle body, composed of numerous fasciculi </li></ul></ul><ul><ul><li>Epimysium </li></ul></ul><ul><ul><ul><li>Surrounds belly of the muscle; helps to hold muscle shape </li></ul></ul></ul><ul><li>Fasciculus </li></ul><ul><ul><li>Bundle of muscle fibers </li></ul></ul><ul><ul><li>Perimysium </li></ul></ul><ul><ul><ul><li>Surrounds and supports individual fasciculi; serves as a vehicle to support nerves and blood vessels </li></ul></ul></ul>
  13. 13. <ul><li>Muscle fiber </li></ul><ul><ul><li>An individual cell with multiple nuclei; contains all the contractile elements within muscle </li></ul></ul><ul><li>Endomysium </li></ul><ul><ul><li>Dense collagen fibril meshwork surrounding each muscle fiber; helps transfer contractile force to the tendon </li></ul></ul><ul><li>Myofibril </li></ul><ul><ul><li>Composes muscle fiber; contains contractile proteins, packaged within each sarcomere </li></ul></ul>
  14. 14. <ul><li>Basic contractile unit of muscle fiber </li></ul><ul><li>Composed of actin and myosin protein filaments </li></ul><ul><li>Sliding filament hypothesis </li></ul><ul><ul><li>Actin filaments slide past the myosin filaments, resulting in contraction of an individual sarcomere </li></ul></ul>
  15. 15. <ul><li>Created when myosin filaments containing numerous “heads”attach to thinner actin filaments </li></ul><ul><li>Myosin head binds an actin filament, flexes, and produces a power stroke between the actin and myosin </li></ul><ul><li>Actin filament slides past the myosin, generating force and shortening a sarcomere </li></ul><ul><li>Simultaneous contraction of sarcomeres shortens entire muscle </li></ul>
  16. 16. <ul><li>Three factors determine functional potential of a muscle: </li></ul><ul><ul><li>Cross-sectional area </li></ul></ul><ul><ul><li>Shape </li></ul></ul><ul><ul><li>Line of pull </li></ul></ul>Mosby items and derived items © 2009 by Mosby, Inc., an affiliate of Elsevier Inc.
  17. 17. <ul><li>Thickness of a muscle, an indirect measure of contractile elements available to generate force </li></ul><ul><li>The larger a muscle’s cross-sectional area, the greater its force potential </li></ul><ul><ul><li>A person with larger muscles can usually generate larger muscular forces </li></ul></ul>
  18. 18. <ul><li>Shape is one important indicator of a muscle’s specific action </li></ul><ul><li>Most muscles are one of four shapes: </li></ul><ul><ul><li>Fusiform </li></ul></ul><ul><ul><li>Triangular </li></ul></ul><ul><ul><li>Rhomboidal </li></ul></ul><ul><ul><li>Pennate </li></ul></ul>
  19. 19. <ul><li>Fusiform muscles </li></ul><ul><ul><li>Fibers run parallel to one another </li></ul></ul><ul><ul><li>Built to provide large ranges of motion </li></ul></ul><ul><ul><li>e.g., biceps brachii </li></ul></ul><ul><li>Triangular muscles </li></ul><ul><ul><li>Expansive proximal attachments converging to a small distal attachment </li></ul></ul><ul><ul><li>Provide a stabilized base for generating force </li></ul></ul><ul><ul><li>e.g., gluteus medius </li></ul></ul>
  20. 20. <ul><li>Rhomboidal muscles </li></ul><ul><ul><li>Expansive proximal and distal attachments </li></ul></ul><ul><ul><li>Shaped like large rhomboids or off-set squares </li></ul></ul><ul><ul><li>Suited to stabilize a joint or provide large forces, depending on cross-sectional area </li></ul></ul><ul><ul><li>e.g., gluteus maximus </li></ul></ul>
  21. 21. <ul><li>Resemble shape of a feather </li></ul><ul><li>Muscle fibers approach a central tendon at an oblique angle </li></ul><ul><li>Large force potential; limited excursion </li></ul><ul><li>Further classified as uni-pennate, bi-pennate, or multi-pennate on the basis of number of fiber sets attached to central tendon </li></ul>
  22. 22. <ul><li>Muscle forces can be described as vectors because they possess both a direction and a magnitude </li></ul><ul><li>Direction of a muscle’s force is referred to as line of pull (or line of force) </li></ul><ul><li>e.g., a muscle’s line of pull that courses anterior to the medial-lateral axis of rotation of the shoulder performs flexion; coursing posterior performs extension </li></ul>
  23. 23. <ul><li>Degree to which muscle is either stretched or shortened at the time of its activation </li></ul><ul><li>Significantly impacts force output of muscle </li></ul><ul><li>Concept that muscle length strongly influences muscle force influences many clinical activities </li></ul><ul><ul><li>e.g., testing and strengthening of muscles </li></ul></ul>
  24. 24. <ul><li>Active length-tension relationship </li></ul><ul><ul><li>Force generated by such a process is highly dependent on sarcomere length </li></ul></ul><ul><ul><li>This relationship in a single sarcomere helps explain how the relative length of a whole muscle affects its force production </li></ul></ul><ul><ul><li>A muscle’s active force is generally greatest at its midlength and least at both extremes </li></ul></ul>
  25. 25. <ul><li>Passive length-tension relationship </li></ul><ul><ul><li>Because of its elasticity, a muscle also produces force passively </li></ul></ul><ul><ul><li>Like a rubber band, a muscle generates greater internal elastic force when stretched </li></ul></ul><ul><ul><li>Elastic behavior is demonstrated by a muscle’s passive length-tension curve </li></ul></ul>
  26. 26. <ul><li>Mono-articular muscles cross one joint; multi-articular muscles cross multiple joints </li></ul><ul><li>A multi-articular muscle can be elongated to a much greater extent than a mono-articular muscle </li></ul><ul><li>The range in force output of a multi-articular muscle can be very large, much greater than a mono-articular muscle </li></ul>
  27. 27. <ul><li>Velocity of a muscular contraction can significantly affect force production </li></ul><ul><li>During a concentric contraction, a muscle produces less force as the speed of contraction increases </li></ul><ul><li>At higher speeds of contraction, actin-myosin cross bridges lack sufficient time to form—pull—and re-form; therefore force is decreased </li></ul>
  28. 28. <ul><li>Isometric activation creates greater force than any speed concentric contraction </li></ul><ul><li>During an eccentric activation, force production increases slightly as the speed of the elongation increases </li></ul>Mosby items and derived items © 2009 by Mosby, Inc., an affiliate of Elsevier Inc.
  29. 29. <ul><li>Muscle held in a shortened position will shorten; muscle held in an elongated position will lengthen </li></ul><ul><li>Disease, immobility, or simply poor posture often results in some degree of “adaptive” shortening </li></ul><ul><li>Contracture is a muscle so tight that it severely restricts joint movement </li></ul>
  30. 30. <ul><li>Overly tight muscle causes associated joints to assume a posture mimicking the muscle’s primary actions—e.g, a tightened hamstring causes hip extension and knee flexion </li></ul><ul><li>Generally, optimal stretching of a muscle requires the therapist to hold a limb in a position opposite to all its actions </li></ul>
  31. 31. <ul><li>Therapists often increase patients’ muscular strength, employing overload and specificity </li></ul><ul><li>Overload principle </li></ul><ul><ul><li>Muscle must receive sufficient level of resistance to stimulate hypertrophy </li></ul></ul><ul><li>Training specificity </li></ul><ul><ul><li>Muscle adapts to the way in which it is challenged </li></ul></ul>Mosby items and derived items © 2009 by Mosby, Inc., an affiliate of Elsevier Inc.
  32. 32. <ul><li>Although ligaments and capsules can stabilize joints, only muscle can adapt to the immediate and long-term external forces that can destabilize the body </li></ul><ul><li>Many types of injuries such as ligamentous rupture can significantly destabilize a joint </li></ul><ul><li>Physical therapists and physical therapist assistants often improve stability of a joint by strengthening the surrounding muscles </li></ul>
  33. 33. <ul><li>Force generated by muscle is the primary means of balancing stable posture and active movement </li></ul><ul><li>Injuries or disease can impair muscular function, causing tightness, weakness, or postural instability </li></ul><ul><li>Fundamental understanding of the nature of muscle can be extremely helpful in determining and advancing a particular course of treatment </li></ul>
  34. 34. <ul><li>Please read Chapter 4 in textbook prior to lecture on Tuesday 01/31/12 </li></ul><ul><li>Quiz #2: Chapters 3 & 4 – Tuesday 01/31/12  </li></ul>

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