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KINE 3301 Biomechanics of Human Movement Muscle Mechanics Chapter 17 Instrumentation used to study muscle forcevelocity and force-length relationship. 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. Sarcomere Force – Length Relationship Force – Length in Normal Joint Range of Motion Force – Velocity Relationship (P + a) V = b (Po – P) 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 DOMS – Damage to Muscle Following Eccentric Contractions Stretch – Shorten Cycle • 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: 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. Stretch – Shorten Cycle The area under the force – length curve is equal to the work done. 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. 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 crossbridges, titin). The SEC explains extra work done in stretch-shorten and EMD. • Parallel Elastic Component (PEC) models passive elastic structures (passive crossbridges, connective tissue: endomysium, perimysium, epimysium, titin, desmin.