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Revision as of 12:33, 24 September 2006 by WLU (talk | contribs) (added reference)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)Concentric Contraction
A type of muscle contraction in which the muscles generates enough force to overcome the resistance (the weight it is carrying) so it shortens as it contracts.
Muscle contraction
A muscle is composed of actin and myosin filaments arranged in parallel with each other, longitudinally throughout the muscle, interdigitating like a deck of cards in mid-shuffle (where one half of the deck is actin, the other is myosin). The actin fibers are thin and fixed, and spread longitudinally through a transverse 'trunk' like branches on a tree. The myosin filaments are thick, and interdigitate between branches and trees, akin to thousands of ropes connecting individual branches. Myosin fibers have individual 'arms' bristling off itself at an angle of approximately 150°, connecting to the actin filaments (like oars in a sculling. It is these arms that generate the force of muscle contraction. When the muscle is stimulated by a nerve to contract, the myosin arms change angle, pulling the trunks of the actin filaments together in a series of ratcheting movements. Once the myosin arm has reached it's greatest change in angle (actually a very minor change) an Adenosine triphosphate molecule is reduced at the connection site, releasing the myosin filament, causing it to return to its original angle and re-attach to the actin filament at a different site. This occurs throughout the length of the muslce, generating force at the musculo-tendinous junction. This causes the muscle to shorten, decreasing the angle of the joint the musculo-tendinous junction. In relation to the elbow and bicep, this would cause the hand to move from close to the leg, to close to the shoulder (a bicep curl).
See also: Eccentric contraction
References
Brooks, G.A, Fahey, T.D. & White, T.P. (1996). Exercise Physiology: Human Bioenergetics and Its Applications. (2nd ed.). Mountain View, California: Mayfield Publishing Co.
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