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5 0 05 displacement mm 1 1 05 0 05 displacement mm 1

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Unformatted text preview: ortening 1.00 work loop force (N) 0.75 muscle lengthening 0.50 + 0.25 0 -1 0.5 0 -0.5 displacement (mm) 1 -1 0.5 0 -0.5 displacement (mm) 1 -1 0.5 0 -0.5 displacement (mm) 1 Work loops - activation phase • Many muscles absorb energy without stimulation. • Stimulation phase influences the shape of the work loop. stress (force) stress strain (length) strain stim Work loops - springs • Not all muscles produce positive work • Muscle can also function as springs. • The compliance can be adjusted by the activation phase. slope = stiffness stress changing activation phase strain Muscles have diverse functions 3. Muscle levers • Muscles work in combination with bones to create levers • All levers have three elements 1.Fulcrum - The joint or point of rotation 2.Load (weight) - The force exerted by the object to be moved 3.Effort - The force exerted by muscle contraction • Mechanics of a lever depends on the position of the three elements Levers Levers that amplify force load effort fulcrum Levers that amplify distance effort load fulcrum Class I levers load fulcrum effort Class II lever effort fulcrum load Class III lever Force advantage and distance advantage • Force advantage is the ratio of length of the effort (force) arm (LFA) to length of the load (weight) arm (LWA). • Distance advantage is the ratio of LWA to LFA. • Most animal levers used for locomotion are Class III levers with low force advantage and high distance advantage. • A small amount of force exerted near the fulcrum causes the mobile end to move quickly over a greater distance Figure 12.21 Class III muscles of foreleg • Cheetah: shorter LFA - Less force, but fast • Lion: longer LFA - More force, but slow Figure 12.22a,b Biological levers class I lever class II lever class III lever E C OEVELYN s.q. LIU L F E L E L F F L L F E E = splenius capitas muscle F E E E = gastrocnemius muscle L F E = biceps brachii muscle Storage of elastic energy • When muscle contracts, it stretches connective tissue and bends bones - Elastic storage energy • When muscle relaxes, stored energy can be released to help in locomotion Elastic extension of spide...
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