Fig. 1.

(A) Kinetics of thin filament regulation and cross-bridge cycling, modeled as coupled three-state cycles. Transition rates (k_ij) between cross-bridge states (X₁–X₃) are strain dependent. Transition rates (r_ij) between thin filament states (T₁–T₃) explicitly encode spatial information about troponin binding Ca²⁺ and tropomyosin movement. B) We simulated force production in a network of linear springs, using spring constants for thick filaments (k_m), thin filaments (k_a) and cross-bridges (k_xb). Thick and thin filament nodes (white circles between springs) represent modeled points from which cross-bridges extend from the thick filament backbone or actin binding sties along the thin filament where cross-bridges. At each time step, Monte-Carlo methods simulate likelihoods of Ca²⁺ regulated cross-bridge attachment to thin filaments, then forces balance about each node throughout the filament lattice.