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. 2004 Jun;123(6):631–641. doi: 10.1085/jgp.200409091

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Copyright © 2004, The Rockefeller University Press

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Figure 4. — 2-μm long myosin containing thick filaments with cross-bridges and 1-μm long actin containing thin filaments are shown. As the sarcomere shortens, the myosin cross-bridges react with actin and propel the thin filaments toward the center of the sarcomere. Both filament types remain at constant lengths during contraction. The sliding of the filaments explains the constancy of the A-band and the changes of the I-band and the H-zone.