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Revision as of 15:37, 25 September 2006 by WLU (talk | contribs) (clarified entry)(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. These fibers interdigitate like thin tree branches (the actin filaments, which act as fixed anchors to capture force generated by the myosin filaments) connected to each other by thick ropes (the myosin filaments, which generate the force). The actin fibers are thin and spread longitudinally towards the musculo-tendinous junctions at either end of the muscle, connected by central trunks that run perpendicular to the main axis of the muscle. 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 boat, though the boat would have two sets of rowers facing each other and pulling in opposite directions). 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, perhaps 20°) 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 site closer to the 'trunk'. This occurs throughout the length of the muscle, generating force at the musculo-tendinous junction, causing the muscle to shorten and decreasing the angle of the joint. 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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