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Muscle Mechanics Chapter 17 KINE 3301 Biomechanics of Human Movement

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Instrumentation used to study muscle force- velocity and force-length relationship.

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Length changes to an individual sarcomere during an isometric contraction. The sarcomere directly underneath the end-plate will be the first to develop tension which causes the sarcomeres to the right and left to lengthen.

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Sarcomere Force Length Relationship

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Force Length in Normal Joint Range of Motion

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Force Velocity Relationship (P + a) V = b (Po P)

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Efficiency of Eccentric & Concentric Exericse Bernard Abbott, Brenda Bigland-Ritchie, JJ Woods Loiselle D S et al. J Appl Physiol 2010;108:1465-1471 2010 by American Physiological Society

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DOMS Damage to Muscle Following Eccentric Contractions

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Stretch Shorten Cycle 1.Stored elastic energy (tendon, cross-bridge, and titin). 2.Eccentric phase elicits a stretch reflex. 3.Eccentric phase pre-loads the muscle, so the concentric phase begins at a higher force. 4.Two joint muscles (rectus femoris, gastrocnemius) transfers energy and allows the muscle to work at a lower velocity and a higher force. The stretch shorten cycle is defined as an eccentric contraction followed by an immediate concentric contraction. Additional work is performed during the concentric phase of a stretch shorten cycle. This extra work is attributed to:

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Stretch Shorten Cycle The area under the force length curve is equal to the work done.

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Effects of Increasing the velocity of stretch on the concentric work done for the concentric phase. 1974 by American Physiological Society Adapted from: Cavagna and Citterio. J Appl Physiol 1974; 239:1-14.

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Three Component Muscle Model Describes the mechanical response of muscle. Contractile Component (CC) models active cross-bridges. Dashpot models muscle viscosity. Series Elastic Component (SEC) models elastic structures in series (tendon, passive cross- bridges, titin). The SEC explains extra work done in stretch-shorten and EMD. Parallel Elastic Component (PEC) models passive elastic structures (passive cross- bridges, connective tissue: endomysium, perimysium, epimysium, titin, desmin.