Model parameters and their sources.

Prime values, such as , represent post-power stroke state values. From Liu et al. (2006) [42], which used insect flight muscle, the most frequently occurring thick filament to S2 angle range is 51–60. We assume that this range is being distorted by the compressive radial force being generated by the rigor cross-bridges in the swollen lattice spacings that Liu et al. used. As such, we choose a rest angle for at the low end of the still common range of 50 to 40. We do not change this angle between states one, two and three. In Taylor et al. (1999) [37] (clearly explained in [43]) the angle between the LCD and the thick filament's axial axis goes from 125 to 70 with the power stroke. The LCD rest length generated by measurements made of structure 1DFK from Houdusse et al. (2000) [36]. The rest values of the 2sXB model's springs are determined by those of the 4sXB model; they are calculated so that the rest position of the 2sXB's head is the same as the rest position of the 4sXB's head. The spring constant, , for the angular spring responsible for each cross-bridge's power stroke is determined by the change in angle over the power stroke and the energy liberated by the hydrolysis of ATP [14]. Additional spring constants are chosen to be consistent with previous work, and to provide sufficient flexibility to enable diffusion. The parameters of the single spring cross-bridge, used for comparison, are taken from [14].