Figure 6. Rate constant of tension redevelopment, k_tr, plotted as a function of level of activation (tension as normalized to maximal fibre tension, Tens/Tens_Max).

Because k_tr exhibits an exponential trend with an increase in the level of activation, the logarithm of k_tr vs. activation was plotted to linearize the trend. Regression analysis determined the intercept of the relationship of k_tr vs. activation, which approximates the apparent rate of XB detachment, g_app (Baker et al. 1998; Palmer & Kentish, 1998; Fitzsimons et al. 2001; Tesi et al. 2002; de Tombe & Stienen, 2007). As show in panel A, the predicted intercept between α-MHC(cTnI) (continuous line) and α-MHC(ssTnI) (dashed line) fibres was not different. As show in panel B, the predicted intercept was slightly lower in β-MHC(cTnI) fibres (continuous line) when compared to β-MHC(ssTnI) fibres (dashed line) was slightly different. This difference in the intercept was significant, suggesting that g_app was slightly faster in β-MHC(ssTnI) vs. β-MHC(cTnI) fibres (Table 1).