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Unformatted text preview: ses greatly and energy is expended – holding a book out to the side Kinds of Muscular Contraction • Two forms of isotonic contraction – concentric contraction­ when a muscle shortens as it maintains tension as when the biceps contract and flexes the elbow – eccentric contraction­ a muscle lengthens as it maintains tension as when your biceps lengthens as you extend your elbow Physiologic Classes of Muscle Fibers • Not all muscle fibers are metabolically alike – slow oxidative, slow twitch, red, or type I fibers­ respond slowly but are relatively resistant to fatigue • soleus muscle of the calf and the postural muscles of the back – fast glycolytic, fast twitch, white or type II fibers­ respond more quickly but also fatigue quickly • gastrocnemius, biceps brachii, muscles of eye movement Muscle Tone (tonus= tension) A sustained partial contraction of portions of a muscle • Hypotonia­ decreased or loss of muscle tone (flaccid) • Hypertonia­ increased muscle tone and is characterized by muscle stiffness. Muscular Atrophy Individual muscle fibers decrease in size owing to a progressive loss of myofibrils (wasting away) • disuse atrophy­ the flow of impulses to inactive muscle is greatly reduced. • denervation atrophy­ complete atrophy when the nerve supply is cut. (6 mo.­ 2yrs. m...
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