To bend; to move a joint in such a direction as to approximate the two parts which it connects. [L. flecto, pp. flexus, to bend]
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Federation Licensing Examination
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flex 'fleks vt
1) to bend esp. repeatedly
2 a) to move muscles so as to cause flexion of (a joint) <stretching and \flexing his knees>
b) to move or tense (a muscle or muscles) by contraction <\flexed their biceps>
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(fleks) [L. flexus bent] to bend or put in a state of flexion.Medical dictionary. 2011.