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. Author manuscript; available in PMC: 2020 Mar 4.
Published in final edited form as: Cond Med. 2019 Oct;2(5):213–224.

Figure 1.

Figure 1.

Sliding filament model of muscle contraction and the cross-bridge cycle. (A) During muscle contraction, the thick (myosin) filaments pull the thin filaments toward the center of the sarcomere. When the thin filaments slide over the thick filaments, the I-bands and H-zones become shorter and eventually disappear. During muscle relaxation, the thick filaments release the interaction with thin filaments, and slide back to their relaxed positions. I-bands and H-zones are widened again. (B) Cross-bridge cycle. 1: Previous cross-bridge cycle ends with the binding of ATP to the myosin head. 2. Weakening actin-myosin interaction leads to releasing of the cross-bridge; 3: ATP is hydrolyzed to ADP and Pi, leading to the “cocking” of the myosin head and ready to bind to actin. The accessibility of AM.ADP. Pi is regulated by troponin complex. 4: Pi is released. The myosin head twists and bends, generating force and pulling the attached actin myofilament ahead. 5. ADP is released. Ready for ATP binding and next cycle.