Figure 4.

Effect of [Ca²⁺] on cross-bridge and muscle kinetics. The relative speed of cross-bridge cycling at six calcium concentrations was estimated by measuring the rate of phase 3 (stretch-activated) tension redevelopment (r₃) after a 2.5% and a 1% ML stretch. The r₃-value was measured by fitting the tension response to the sum of three exponential curves (see Materials and Methods). The data were obtained from 11 fibers. The dependence of muscle speed on [Ca²⁺] was measured by determining the frequency at which maximum power was generated (f_max) using small-amplitude sinusoidal analysis. The data were obtained from seven fibers. Values are mean ± SE.