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    chapter 03 week 2 lecture 2 chapter 03 week 2 lecture 2 Presentation Transcript

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