(see also "Several Insights into muscle contraction mechanism" part 1 and 2)


During active contraction at sarcomere lengths less than 2.05 micrometer, double overlap of thin filaments from opposite ends of the sarcomere starts to occur.

According to the cross-bridge theory, such a double overlap should not exist, simply because when a thin filament crosses the sarcomere M band, the cross-bridges belonging to that halves of  thick filaments situated in the opposite side of the sarcomere are supposed to produce a force that will push away the thin filament extremities. If the pointed end of the thin filaments were free, at coming in contact they reciprocally would hinder each other until eventually they will change their direction of advancement along the thick filaments.


     However, this phenomenon never happens, possibly because the so called "free ends" of the thin filaments are connected by contractile threads to the Z line in the opposite edge of the sarcomere.