Summary of computational results for the model fit of ktr–pCa relationship in murine and porcine myocardium (Table S1). The model is run with parameter sets 1, 2, and 8 with fitted rate constants taken from Table 2. The values of B, C, M₁, and M₂ are recorded when the solution of the ODE system Eqs. 2, 3, and 4 reach their equilibrium state at maximal activation. K, the activation factor $(K=kBC/kCB)$⁠; N, the crossbridge recruitment factor $(N=kCM1/kM1C)$⁠; λ_cyc, the fraction of crossbridges participating in crossbridge cycling $(λcyc=C+M1+M2)$⁠; and λ_cyc^M2, the fraction of cycling crossbridges that generate force $(λcycM2=M2/λcyc)$ is computed based on these values. Finally, ktr is computed according to the slack-restretch maneuver described by Patel et al. (2023).