Force redevelopment and decay rates in permeabilized slow-twitch skeletal muscle fiber preparations before (black) and after (green) PKA treatment as a function of Ca²⁺ activation levels. (A and B) PKA increased the rate constants (s⁻¹) of both the fast phase (k₁, A) and slow phase (k₂, B) of force redevelopment at all Ca²⁺ activation levels. Values at low relative force levels are shown in insets. (C) t_1/2 following PKA treatment had the tendency of being faster; however, it was only significantly faster at 50% Ca²⁺ activation. There was no t_1/2 at maximum Ca²⁺ activation due to the lack of a transient force overshoot (n = 4). *, P < 0.05 using paired t test analysis.