Cl- conductance makes up ~80% of the resting muscle membrane potential. Loss of function mutations of the muscle chloride channel (CLC-1) cause electrical hyperexcitability resulting in involuntary action potential bursts and contractions. Myotonic stiffness is most prominent when a muscle has rested and is then strenuously activated. With continued activity myotonia decreases, a phenomenon called warm-up. Independent of the etiology, myotonic stiffness is considered to exhibit a pathologically increased temperature dependence. Here, we studied the effects of temperature and stimulation frequency on the parameters of contraction and relaxation of skeletal muscle strips. Increase of the electrical stimulation frequency accelerated the onset of the warm-up in experimental myotonia. The twitch contraction and relaxation parameters were strongly temperature dependent in an exponential manner. However, there was no sicnificant difference between myotonic and control muscle. Above 37°C myotonic activity was absent. Maximum twitch force and baseline tension increased with temperature. We conclude that although the warm-up phenomenon can be enhanced in low Cl- conductance myotonia by fast movements and by an increase in muscle temperature the results contradict the prevailing opinion that the temperature dependence is pathologically increased in chloride channel myotonia. A particular cold-induced myotonia seems to be confined to Na+ channel myotonia.