Figure 1.

Force response to a sudden 2% stretch. (A) A representative 2% increase in ML imposed on a control (untreated) guinea pig cardiac muscle fiber at maximal Ca²⁺ activation (pCa 4.3). (B) The corresponding force responses normalized to the isometric steady-state force (F_ss) before ML change. Different phases (dashed lines) from which respective parameters were estimated are highlighted. F₁, the instantaneous increase in force due to sudden increase in ML (phase 1); c, the rate at which the sudden ML-induced strain within force-bearing XBs dissipates to a minimal force point (phase 2); b, the rate of delayed force rise after an increase in ML (phase 3); F_nss, the new steady-state force corresponding to an increase in ML.