Muscle velocity recovery cycles: a tool to study muscle membrane properties in vivo

In recent studies of nerve excitability, the recovery cycle after a single supramaximal stimulus has been found to provide useful information about axonal membrane potential and ion channel function in neuropathies. We have adapted this method to human muscle fibres, by measuring the changes in conduction velocity of brachioradialis muscle fibres following one or two conditioning impulses, using direct muscle stimulation and recording via needle electrodes. In normal subjects the relative refractory period is followed by a phase of supernormality, which reaches a peak velocity increase of just under 10% at ˜6ms…