Fig. 3.

Schematic diagram of a half-sarcomere composed of two filaments. Reproduced with permission from Campbell [5]. a The spacing of myosin heads along the thick filament is a non-integer multiple of the spacing of binding sites on the thin filament. There are therefore positions (e.g., myosin 10) where a myosin head is aligned close to a binding site on actin and places (e.g., myosin 14) where the myosin head may be positioned too far from a binding site to attach. b If the filaments extend slightly when a myosin head generates force, additional myosin heads may be pulled close enough to actin sites that they can interact with them