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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
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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
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The 4 Roles of Muscle
- Agonist
- Antagonist
- Stabilizer
- Neutralizer
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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.
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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.
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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.
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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)
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3 Factors that Affect the Magnitude of Muscle Contraction Force
- Physiological Cross-Sectional Area
- Muscle Length
- Contraction Velocity
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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
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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.
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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
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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.
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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.
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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.
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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.
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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
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