- Antagonist (muscle)
An antagonist is a classification used to describe a
muscle that acts in opposition to the specific movement generated by the agonist and is responsible for returning a limb to its initial position.Antagonistic pairs
Antagonistic muscles are found in pairs called antagonistic pairs. These consist of an
extensor muscle , which "opens" the joint (i.e. increasing the angle between the two bones), and aflexor muscle , which does the opposite to anextensor muscle .Antagonistic pairs are needed in the body because muscles can only exert a pulling force, and can't push themselves back into their original positions. An example of this kind of muscle pairing is like the
biceps andtriceps .When the biceps are contracting, the triceps are relaxed, and are able to be stretched back to its original position. This is the opposite when the triceps are contracting.Lombard direct Paradox When you stand up from a sitting position, both the
hamstrings andquadriceps contract at the same time.The Rectus Femoris biarticular muscle acting over the hip, when compared to the hamstrings has a smaller hip movement arm. But, the rectus femoris movement arm is greater over the knee, than the hamstring's knee movement. This means that contraction from both rectus femoris and hamstrings will result in hip extension, and knee extension. Hip extension will also add a passive stretch component to the Rectus Femoris, and will result in a knee extension force. This "paradox" allows for efficient movement especially during gait. [http://moon.ouhsc.edu/dthompso/namics/lombard.htm]
ee also
*
Hering's law of equal innervation
*Sherrington's law of reciprocal innervation
*Hayes's law of equal innervation External links
* [http://www.ifafitness.com/book1/kinesiology.htm Examples of antagonists]
* [http://webanatomy.net/anatomy/muscle_actions.htm Examples of antagonists]More links
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