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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)