A. General Description Myotonia is a bizarre syndrome seen in several classic hereditary muscle diseases of humans and animals, and occasionally in response to chemicals or disease (Rudel

and Lehmann-Horn, 1985). Because myotonia is usually directly related to altered excitability involving ion channels, it illustrates the consequence of ion channel dysfunction. Myotonic individuals experience additional contraction of their muscles during and following a voluntary (willed) effort, especially after a period of inactivity. This extra contraction can produce stiffness that hinders normal movement . With repeated efforts, within a short period of time the condition lessens and normal movements can be made. This so-called warm-up effect disappears after a new period of inactivity of several minutes, and the myotonic stiffness returns. The biophysical bases for the repetitive excitability is established in most instances, but the mechanism of warm-up is not fully understood.