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muscle contractionThe movement of muscle fibres in response to force or load.
Muscle contraction types
• Concentric—The muscle shortens in length as it overcomes resistance.
• Eccentric—The muscle increases in length to accommodate resistance.
• Isometric—The muscle resists outside stress without exhibiting motion.
muscle contractionthe process of force-generation in the fibres of any class of muscle, by the interaction of myosin head-groups in the thick filaments with actin molecules in one of the immediately neighbouring thin filaments. This is set in train ('activated') by a rise in the concentration of calcium ions [Ca2+] in the muscle fibre cytoplasm in all types of muscle, but the mechanism for this rise differs in important respects between them. With reference to skeletal muscle, 'contraction', though literally implying shortening, is used to describe force-generation, whether it actually results in shortening (concentric action), tension without movement (isometric action) or even lengthening against the muscle's own resistance (eccentric action); the last is sometimes called an 'eccentric contraction' or, even worse, a 'lengthening contraction' - paradoxical usages better avoided. See also excitation-contraction coupling, force-velocity relationship, myofibrils.
muscle contraction; voluntary muscle contraction; muscle twitch tension generated within muscle tissue, due to actin/myosin interaction, during which muscle length shortens, lengthens or remains unchanged (contrast with concentric muscle contraction, below); see agonist; antagonist; insertion; fixator; origin; synergist
concentric muscle contraction acceleration force generated within contracting agonist muscle tissue, by actin/myosin interaction; agonist muscle force overcomes antagonist muscle resistance, creating a net reduction in length of agonist muscle (see entry above)
eccentric muscle contraction deceleration force generated by interaction of actin/myosin of contracting antagonist muscle tissue; antagonist muscle force is insufficient to overcome agonist muscle resistance, creating a net increase in length of antagonist muscle
isometric muscle contraction muscle contraction that increases muscle tension, whilst maintaining constant overall muscle length; characteristic of e.g. intrinsic foot muscles which stabilize the toes against the support surface during weight-bearing, and the overall muscle length remains constant despite increasing muscle tension
isotonic muscle contraction muscle contraction with overall shortening of muscle length, in response to applied load, characteristic of e.g. leg muscles when lifting a heavy weight, using a combination of balanced concentric and eccentric contractions within limb, back and abdominal muscle groups; maximal generated muscle force is greater than total applied load