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09 10 Muscle Contraction I and II

Isometric contraction length tension relationship

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Isometric Contraction: Length-Tension Relationship Single Twitch, Twitch Summation, and Tetanus Isotonic Contraction: Force-Velocity Relationship
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Motor Units
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Motor Unit Recruitment Motor Unit : One motor neuron plus all of the muscle fibers it innervates Motor Unit Recruitment : Stimulation of multiple motor neurons and multiple motor units to achieve stronger contractions Small Motor Units : For fine movements Large Motor Units : For coarse powerful movements
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Muscle Twitch, Twitch Summation, and Tetanus Single Twitch : Muscle contraction triggered by one action potential Twitch Summation : Partial overlapping of multiple twitches Tetanus : Complete overlapping of multiple twitches
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Isometric Contraction
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Isometric Contraction Length-Tension Relationship Isometric Contraction : Force generation at a constant muscle length (e.g. for posture control) Length-Tension Relationship : Contractile force is dependent on muscle length Optimal Length : Muscle length at which contractile force is maximal Mechanism : Length-dependent overlap of actin and myosin filaments
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Mechanism of Length-Tension Relation in Isometric Contractions
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Temporal Summation of Isometric Contractions
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Temporal Summation in Skeletal Muscle Contraction
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Isotonic Contraction
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Isotonic Contraction Force-Velocity Relationship Isotonic Contraction : Muscle shortening against a constant external load (~weight lifting) Force-Velocity Relationship: Shortening velocity is dependent on external load Maximum Shortening Velocity : Occurs at zero external load Zero Shortening Velocity : Occurs at maximum load - same as isometric contraction
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Isotonic Shortening During a Single Twitch Against Different External Loads
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Force-Velocity Relation in Isotonic Contractions
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Muscle Power Output Power Output = Force x Velocity Isometric Contraction : Zero power output - because shortening velocity is zero Maximum Shortening Velocity : Zero power output - because external force is zero Maximum power output occurs at intermediate shortening velocity - against ~30% isometric force
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Power Output During Muscle Contraction Power = Force x Velocity
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Power-Velocity Relations During Maximal Cycling (From: Exerc. Sport Sci. Rev. 35: 74-81, 2007)
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Skeletal Muscle Metabolism and Fiber Types Sources of ATP for Muscle Contraction Muscle Fiber Types
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Sources of ATP for Muscle Contraction
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