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Muscle Contractions Isometric A contraction involving no change in muscle length There is no movement with an isometric contraction (ex. Pushing your hand against your desk) Isotonic A contraction that involves the shortening or lengthening of a muscle while force is being applied to the muscle Two Types of Isotonic Contractions o Concentric: The shortening of the muscle as force is being placed upon it. Example: The biceps brachii shortening on the up-phase of a bicep curl o Eccentric: The lengthening of the muscle as force is being placed upon it. Example: The biceps brachii lengthening on the down-phase of a bicep curl o Examples of Concentric & Eccentric Contractions occurring simultaneously Bicep Curl (Up Phase) Concentric: Biceps Eccentric: Triceps Bicep Curl (Down Phase) Concentric: Triceps Eccentric: Biceps Bench Press (Up Phase) Concentric: Chest muscles, Triceps, Deltoid (Front & Mid 1/3) Eccentric: Biceps, Upper Back Muscles, Deltoid (Back 1/3) Bench Press (Down Phase) Concentric: Biceps, Upper Back Muscles, Deltoid (Back 1/3) Eccentric: Chest Muscles, Triceps, Deltoid (Front & Mid 1/3) Roles of Muscles Four Roles Muscles Play Agonist Antagonist Stabilizer or Fixator Neutralizer or Synergist Definitions Agonist Muscles that concentrically contract to cause a movement. Example: Biceps contracting during the up phase of a curl Antagonist Muscles that eccentrically contract to oppose a movement. Example: Triceps contracting during the up phase of a curl Stabilizer/Fixator A muscle concentrically contracting to prevent/stabilize movement of another muscle/structure Example: During water skiing, the rhomboids contract to stabilize the scapula against the pull of the tow rope. Neutralizer/Synergist A muscle that concentrically contracts to prevent or eliminate an unwanted action produced by the agonist muscle Example: When the biceps brachii concentrically contracts to perform elbow flexion, the pronator teres must contract to prevent supination from also occurring at the elbow **Performance of human movements involves multiple muscle groups to act together. Example: Lifting a glass of water Stabilizers Agonists Scapula Muscles Wrist Flexors Wrist Extensors Finger Flexors Elbow Flexors Shoulder Flexors Neutralizers Antagonists Mid 1/3 of Deltoid Supraspinatus Elbow Extensors (partially controls movement speed & motion)