Changes in twitch tension predicted by the five-state model for change in $k + H$ up to ±50% from those used in Fig. 3 (dark green line), denoted as orig. $k + H .$ The main effect of changes in $k+H$ on the tension responses are displayed in modest changes in the peak tension, resting tension, the rate of tension rise, and the rate of relaxation. For all values of $k+H,$ the rate of relaxation is about twofold slower than that observed.