FiberSim describes the contraction of a half-sarcomere composed of thin and thick filaments. The muscle cross-section presents a hexagonal lattice as shown below. Each thick filament is surrounded by six thin filaments, while each thin filament has three neighboring thick filaments.
The number of thick filaments, \(m_n\), is specified in the model JSON file, and must be a square number. The number of thin filaments is then defined as \(2 . m_n\). Some thin filaments are mirrored on the edge of the lattice to ensure that each thick and thin filament has a correct number of neighbors. An example of a generated lattice for \(m_n = 4\) is shown below.