Mean voltage distribution of the “on” charge from (A) seven control fibers and (B) nine mdx muscle fibers. Superimposed solid lines correspond to the result from fitting the two-state Boltzmann distribution to the mean data points. In control and in mdx, this gave values for Qmax, V0.5, and k of 21.9 nC/μF, −38 mV, and 13.5 mV, and 21.9 nC/μF, −38 mV, and 13.8 mV, respectively.