KIN 158 Chapter 11

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KIN 158 Chapter 11
2011-04-04 19:23:44
Chapter Muscular System Motors Body

Chapter 11 Muscular System- The Motors of the Body
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  1. Muscular Contractions
    • Distinguishing characteristic of muscle is its ability to contract.
    • The development of tension within a muscle causing it to pull on its attachments
  2. Types of Muscular Contractions
    • Concentric (shorten)- when a muscle is active and its attachments draw closer together
    • Eccentric (lengthens)- when a muscle is active and its attachments are drawn farther apart
    • Isometric (no change)- when a muscle is active and its attachments do not move relative to each other
  3. The 4 Roles of Muscle
    • Agonist
    • Antagonist
    • Stabilizer
    • Neutralizer
  4. Agonist, definition of
    • What motion is occurring? What is causing it? If a muscle caused it, then that is the agonist.
    • Muscles capable of creating a torque in the same direction as the joint action referred to.
    • Muscles that are active concentrically are agonists to the action occurring at the joint they cross.
  5. Antagonist, definition of
    • Muscles capable of creating a torque opposite the joint action referred to or opposite the other muscle referred to.
    • Term antagonist can be used in reference to a joint action. Muscles active eccentrically are antagonists to the action occurring at the joint they cross.
    • Antagonist may also be used in reference to another muscle. The torque the antagonist creates opposes the torque created by the muscle referred to.
  6. Stabilizer, definition of
    • "Removes instabilities"
    • Muscles that are active isometrically to keep a limb from moving when the reference muscle contracts.
    • When a muscle is active, it will tend to move both bones to which it is attached.
    • The isometric action of the stabilizing muscles keeps unwanted movement at the joint from occurring.
  7. Neutralizer, definition of
    • "Eliminates the other movements, joint rotations"
    • Muscle that creates a torque to oppose an undesired action of another muscle.
    • The torque created by many muscles (Ex. biceps brachii) components in several planes.
    • If only one joint movement is desired (Ex. friction), the neutralizer acts to oppose the unwanted movements (Ex. forearm supination or shoulder flexion)
  8. 3 Factors that Affect the Magnitude of Muscle Contraction Force
    • Physiological Cross-Sectional Area
    • Muscle Length
    • Contraction Velocity
  9. Physiological Cross-Sectional Area
    • Muscles behave similarly to rubber bands- increasing the number of fibers side by side and parallel to each other increases the strength of the muscle.
    • PCSA of the muscle perpendicular to the muscle fibers and line of pull of a muscle gives an indication of the maximal tensile force a longitudinal muscle can produce
  10. PCSA continued (2)...
    • The maximum tensile force a pennate muscle can produce cannot be estimated by the cross-sectional area perpendicular to the muscle fibers and line of pull of a muscle.
    • The muscle fibers and line of pull of a pennate muscle are not in the same direction
    • A cross section taken perpendicular to the line of pull of a pennate muscle would not include all the fibers of the muscle.
  11. PCSA continued (3)...
    Longitudinal versus Pennate
    • Pennate muscles allows more fibers (force) compared to longitudinal muscles.
    • Varied movements
    • Less energy to do so
    • Muscle fibers are short
    • Longitudinal allows big ranges of motion
  12. PCSA continued (4)
    Longitudinal Versus Pennate (2)
    • An equivalent volume of pennate muscle will generate more tensile force than a longitudinal muscle.
    • However, there is a drawback to pennate muscles- the shorter fibers of the pennate muscle and their orientation relative to the angle of pull, limit the distance over which a pennate muscle can shorten.
  13. Muscle Length
    (2 of 3 factors that affect the magnitude of muscle contraction force)
    • Maximum muscle force is also dependent on the length of the muscle.
    • Total muscle tension developed depends on- active tension developed by the contractile elements, plus the passive tension developed when the muscle is stretched beyond its resting length.
  14. Contraction Velocity
    (3 of 3 factors that affect the magnitude of muscle contraction force)
    Maximum tensile force developed by a muscle is dependent on the velocity of shortening, as well as its length.
  15. The Relationship between muscle length and tension.
    (Figure Curve)
    • Need to stretch the muscles
    • This curve shows that you can't perform both maximum contraction and full range of motion.
  16. Contraction Velocity Figure
    • Concentric, Eccentric and Isometric Activity
    • Negative velocities of shortening represent eccentric contractions.
    • A muscle contracting eccentrically or isometrically is capable of producing more force than a muscle contracting concentrically.
    • Bench press example. Figure 11.17